Module java.base
Package java.lang

Class Thread

java.lang.Object
java.lang.Thread
All Implemented Interfaces:
Runnable
Direct Known Subclasses:
ForkJoinWorkerThread

public class Thread extends Object implements Runnable
A thread is a thread of execution in a program. The Java virtual machine allows an application to have multiple threads of execution running concurrently.

Thread provides a Thread.Builder and other APIs to create and start threads that execute Runnable tasks. Starting a thread schedules it to execute concurrently with the thread that caused it start. The newly started thread invokes the task's run method. Thread defines the join method to wait for a thread to terminate.

Threads have a unique identifier and a name. The identifier is generated when a Thread is created and cannot be changed. The thread name can be specified when creating a thread or can be changed at a later time.

Threads support ThreadLocal variables. These are variables that are local to a thread, meaning a thread can have a copy of a variable that is set to a value that is independent of the value set by other threads. Thread also supports InheritableThreadLocal variables that are thread local variables that are inherited from the parent thread. Thread supports a special inheritable thread local for the thread context-class-loader.

Platform threads

Thread supports the creation of platform threads that are typically mapped 1:1 to kernel threads scheduled by the operating system. Platform threads will usually have a large stack and other resources that are maintained by the operating system. Platforms threads are suitable for executing all types of tasks but may be a limited resource.

Platform threads are designated daemon or non-daemon threads. When the Java virtual machine starts up, there is usually one non-daemon thread (the thread that typically calls the application's main method). The Java virtual machine terminates when all started non-daemon threads have terminated. Unstarted daemon threads do not prevent the Java virtual machine from termination. The Java virtual machine can also be terminated by invoking the Runtime.exit(int) method, in which case it will terminate even if there are non-daemon threads still running.

In addition to the daemon status, platform threads have a thread priority and are members of a thread group.

Platform threads get an automatically generated thread name by default.

Virtual threads

Thread also supports the creation of virtual threads. Virtual threads are typically user-mode threads scheduled by the Java virtual machine rather than the operating system. Virtual threads will typically require few resources and a single Java virtual machine may support millions of virtual threads. Virtual threads are suitable for executing tasks that spend most of the time blocked, often waiting for I/O operations to complete. Virtual threads are not intended for long running CPU intensive operations.

Virtual threads typically employ a small set of platform threads are use as carrier threads. Locking and I/O operations are the scheduling points where a carrier thread is re-scheduled from one virtual thread to another. Code executing in a virtual thread will usually not be aware of the underlying carrier thread, and in particular, the currentThread() method, to obtain a reference to the current thread, will return the Thread object for the virtual thread, not the underlying carrier thread.

Virtual threads gets a fixed name by default.

Creating and starting threads

As noted above, Thread defines a Thread.Builder API for creating and starting threads. The ofPlatform() and ofVirtual() methods are used to create builders for platform and virtual threads respectively. The following are examples that use the builder:


   Runnable runnable = ...

   // Start a daemon thread to run a task
   Thread thread = Thread.ofPlatform().daemon().start(runnable);

   // Create an unstarted thread with name "duke", its start() method
   // must be invoked to schedule it to execute.
   Thread thread = Thread.ofPlatform().name("duke").unstarted(runnable);

   // A ThreadFactory that creates daemon threads named "worker-0", "worker-1", ...
   ThreadFactory factory = Thread.ofPlatform().daemon().name("worker-", 0).factory();

   // Start a virtual thread to run a task
   Thread thread = Thread.ofVirtual().start(runnable);

   // A ThreadFactory that creates virtual threads
   ThreadFactory factory = Thread.ofVirtual().factory();
 

In addition to the builder, Thread defines (for historical and customization reasons) public constructors for creating platform threads. Most applications should have little need to use these constructors directly or extend Thread. The constructors cannot be used to create virtual threads.

Inheritance

Creating a Thread will inherit, by default, the initial values of InheritableThreadLocal variables, inheritable-scoped-variables, and a number of properties from the parent thread:
  • Platform threads inherit the daemon status, priority, and thread-group.
  • Virtual threads are scheduled by the same scheduler as the parent thread when the parent thread is a virtual thread. Virtual threads use the default scheduler when the parent thread is a platform thread and the scheduler has not been selected.

Unless otherwise specified, passing a null argument to a constructor or method in this class will cause a NullPointerException to be thrown.

Since:
1.0
  • Nested Class Summary

    Nested Classes
    Modifier and Type
    Class
    Description
    static interface 
    A builder for Thread and ThreadFactory objects.
    static class 
    A thread state.
    static interface 
    Interface for handlers invoked when a Thread abruptly terminates due to an uncaught exception.
    static interface 
    The task submitted to a custom scheduler.
  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static int
    The maximum priority that a platform thread can have.
    static int
    The minimum priority that a platform thread can have.
    static int
    The default priority that is assigned to a thread.
  • Constructor Summary

    Constructors
    Constructor
    Description
    Allocates a new platform Thread.
    Thread​(Runnable task)
    Allocates a new platform Thread.
    Thread​(Runnable task, String name)
    Allocates a new platform Thread.
    Thread​(String name)
    Allocates a new platform Thread.
    Thread​(ThreadGroup group, Runnable task)
    Allocates a new platform Thread.
    Thread​(ThreadGroup group, Runnable task, String name)
    Allocates a new platform Thread so that it has task as its run object, has the specified name as its name, and belongs to the thread group referred to by group.
    Thread​(ThreadGroup group, Runnable task, String name, long stackSize)
    Allocates a new platform Thread so that it has task as its run object, has the specified name as its name, and belongs to the thread group referred to by group, and has the specified stack size.
    Thread​(ThreadGroup group, Runnable task, String name, long stackSize, boolean inheritInheritableThreadLocals)
    Allocates a new platform Thread so that it has task as its run object, has the specified name as its name, belongs to the thread group referred to by group, has the specified stackSize, and inherits initial values for inheritable thread-local variables if inheritThreadLocals is true.
    Thread​(ThreadGroup group, String name)
    Allocates a new platform Thread.
  • Method Summary

    Modifier and Type
    Method
    Description
    static int
    Deprecated.
    This method is obsolete.
    void
    Determines if the currently running thread has permission to modify this thread.
    protected Object
    Throws CloneNotSupportedException as a Thread can not be meaningfully cloned.
    int
    Deprecated, for removal: This API element is subject to removal in a future version.
    This method was originally designed to count the number of stack frames but the results were never well-defined and it depended on thread-suspension.
    static Thread
    Returns the Thread object for the current thread.
    static void
    Prints a stack trace of the current thread to the standard error stream.
    static int
    enumerate​(Thread[] tarray)
    Deprecated.
    This method is obsolete.
    Returns a map of stack traces for all live threads that are scheduled by the operating system.
    Returns the context ClassLoader for this thread.
    Returns the default handler invoked when a thread abruptly terminates due to an uncaught exception.
    long
    Returns the identifier of this Thread.
    Returns this thread's name.
    int
    Returns this thread's priority.
    Returns an array of stack trace elements representing the stack dump of this thread.
    Returns the state of this thread.
    Returns the thread group to which this thread belongs.
    Returns the handler invoked when this thread abruptly terminates due to an uncaught exception.
    static boolean
    holdsLock​(Object obj)
    Returns true if and only if the current thread holds the monitor lock on the specified object.
    void
    Interrupts this thread.
    static boolean
    Tests whether the current thread has been interrupted.
    boolean
    Tests if this thread is alive.
    boolean
    Tests if this thread is a daemon thread.
    boolean
    Tests whether this thread has been interrupted.
    boolean
    Returns true if this thread is a virtual thread.
    void
    Waits for this thread to terminate.
    void
    join​(long millis)
    Waits at most millis milliseconds for this thread to terminate.
    void
    join​(long millis, int nanos)
    Waits at most millis milliseconds plus nanos nanoseconds for this thread to terminate.
    boolean
    join​(Duration duration)
    Waits for this thread to terminate for up to the given waiting duration.
    Returns a builder for creating a platform Thread or ThreadFactory that creates platform threads.
    Returns a builder for creating a virtual Thread or ThreadFactory that creates virtual threads.
    static void
    Indicates that the caller is momentarily unable to progress, until the occurrence of one or more actions on the part of other activities.
    void
    Deprecated, for removal: This API element is subject to removal in a future version.
    This method exists solely for use with suspend(), which has been deprecated because it is deadlock-prone.
    void
    run()
    If this thread was constructed using a separate Runnable run object, then that Runnable object's run method is called; otherwise, this method does nothing and returns.
    void
    Sets the context ClassLoader for this thread.
    void
    setDaemon​(boolean on)
    Marks this thread as either a daemon thread or a user thread.
    static void
    Set the default handler invoked when a thread abruptly terminates due to an uncaught exception, and no other handler has been defined for that thread.
    void
    setName​(String name)
    Changes the name of this thread to be equal to the argument name.
    void
    setPriority​(int newPriority)
    Changes the priority of this thread.
    void
    Set the handler invoked when this thread abruptly terminates due to an uncaught exception.
    static void
    sleep​(long millis)
    Causes the currently executing thread to sleep (temporarily cease execution) for the specified number of milliseconds, subject to the precision and accuracy of system timers and schedulers.
    static void
    sleep​(long millis, int nanos)
    Causes the currently executing thread to sleep (temporarily cease execution) for the specified number of milliseconds plus the specified number of nanoseconds, subject to the precision and accuracy of system timers and schedulers.
    static void
    sleep​(Duration duration)
    Causes the currently executing thread to sleep (temporarily cease execution) for the specified duration, subject to the precision and accuracy of system timers and schedulers.
    void
    Schedules this thread to begin execution.
    static Thread
    Creates a virtual thread to execute a task and schedules it to execute.
    void
    Deprecated, for removal: This API element is subject to removal in a future version.
    This method is inherently unsafe.
    void
    Deprecated, for removal: This API element is subject to removal in a future version.
    This method has been deprecated, as it is inherently deadlock-prone.
    Returns a string representation of this thread.
    static void
    A hint to the scheduler that the current thread is willing to yield its current use of a processor.

    Methods declared in class java.lang.Object

    equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
  • Field Details

    • MIN_PRIORITY

      public static final int MIN_PRIORITY
      The minimum priority that a platform thread can have.
      See Also:
      Constant Field Values
    • NORM_PRIORITY

      public static final int NORM_PRIORITY
      The default priority that is assigned to a thread.
      See Also:
      Constant Field Values
    • MAX_PRIORITY

      public static final int MAX_PRIORITY
      The maximum priority that a platform thread can have.
      See Also:
      Constant Field Values
  • Constructor Details

    • Thread

      public Thread()
      Allocates a new platform Thread. This constructor has the same effect as Thread (null, null, gname), where gname is a newly generated name. Automatically generated names are of the form "Thread-"+n, where n is an integer.

      This constructor is only useful when extending Thread to override the run() method.

      See Also:
      Inheritance
    • Thread

      public Thread(Runnable task)
      Allocates a new platform Thread. This constructor has the same effect as Thread (null, task, gname), where gname is a newly generated name. Automatically generated names are of the form "Thread-"+n, where n is an integer.

      For a non-null task, invoking this constructor directly is equivalent to:

      Thread.ofPlatform().unstarted(task); 
      Parameters:
      task - the object whose run method is invoked when this thread is started. If null, this classes run method does nothing.
      See Also:
      Inheritance
    • Thread

      public Thread(ThreadGroup group, Runnable task)
      Allocates a new platform Thread. This constructor has the same effect as Thread (group, task, gname) ,where gname is a newly generated name. Automatically generated names are of the form "Thread-"+n, where n is an integer.

      For a non-null group and task, invoking this constructor directly is equivalent to:

      Thread.ofPlatform().group(group).unstarted(task); 
      Parameters:
      group - the thread group. If null and there is a security manager, the group is determined by SecurityManager.getThreadGroup(). If there is not a security manager or SecurityManager.getThreadGroup() returns null, the group is set to the current thread's thread group.
      task - the object whose run method is invoked when this thread is started. If null, this thread's run method is invoked.
      Throws:
      SecurityException - if the current thread cannot create a thread in the specified thread group
      See Also:
      Inheritance
    • Thread

      public Thread(String name)
      Allocates a new platform Thread. This constructor has the same effect as Thread (null, null, name).

      This constructor is only useful when extending Thread to override the run() method.

      Parameters:
      name - the name of the new thread
      See Also:
      Inheritance
    • Thread

      public Thread(ThreadGroup group, String name)
      Allocates a new platform Thread. This constructor has the same effect as Thread (group, null, name).

      This constructor is only useful when extending Thread to override the run() method.

      Parameters:
      group - the thread group. If null and there is a security manager, the group is determined by SecurityManager.getThreadGroup(). If there is not a security manager or SecurityManager.getThreadGroup() returns null, the group is set to the current thread's thread group.
      name - the name of the new thread
      Throws:
      SecurityException - if the current thread cannot create a thread in the specified thread group
      See Also:
      Inheritance
    • Thread

      public Thread(Runnable task, String name)
      Allocates a new platform Thread. This constructor has the same effect as Thread (null, task, name).

      For a non-null task and name, invoking this constructor directly is equivalent to:

      Thread.ofPlatform().name(name).unstarted(task); 
      Parameters:
      task - the object whose run method is invoked when this thread is started. If null, this thread's run method is invoked.
      name - the name of the new thread
      See Also:
      Inheritance
    • Thread

      public Thread(ThreadGroup group, Runnable task, String name)
      Allocates a new platform Thread so that it has task as its run object, has the specified name as its name, and belongs to the thread group referred to by group.

      If there is a security manager, its checkAccess method is invoked with the ThreadGroup as its argument.

      In addition, its checkPermission method is invoked with the RuntimePermission("enableContextClassLoaderOverride") permission when invoked directly or indirectly by the constructor of a subclass which overrides the getContextClassLoader or setContextClassLoader methods.

      The priority of the newly created thread is the smaller of priority of the thread creating it and the maximum permitted priority of the thread group. The method setPriority may be used to change the priority to a new value.

      The newly created thread is initially marked as being a daemon thread if and only if the thread creating it is currently marked as a daemon thread. The method setDaemon may be used to change whether or not a thread is a daemon.

      For a non-null group, task, and name, invoking this constructor directly is equivalent to:

      Thread.ofPlatform().group(group).name(name).unstarted(task); 
      Parameters:
      group - the thread group. If null and there is a security manager, the group is determined by SecurityManager.getThreadGroup(). If there is not a security manager or SecurityManager.getThreadGroup() returns null, the group is set to the current thread's thread group.
      task - the object whose run method is invoked when this thread is started. If null, this thread's run method is invoked.
      name - the name of the new thread
      Throws:
      SecurityException - if the current thread cannot create a thread in the specified thread group or cannot override the context class loader methods.
      See Also:
      Inheritance
    • Thread

      public Thread(ThreadGroup group, Runnable task, String name, long stackSize)
      Allocates a new platform Thread so that it has task as its run object, has the specified name as its name, and belongs to the thread group referred to by group, and has the specified stack size.

      This constructor is identical to Thread(ThreadGroup,Runnable,String) with the exception of the fact that it allows the thread stack size to be specified. The stack size is the approximate number of bytes of address space that the virtual machine is to allocate for this thread's stack. The effect of the stackSize parameter, if any, is highly platform dependent.

      On some platforms, specifying a higher value for the stackSize parameter may allow a thread to achieve greater recursion depth before throwing a StackOverflowError. Similarly, specifying a lower value may allow a greater number of threads to exist concurrently without throwing an OutOfMemoryError (or other internal error). The details of the relationship between the value of the stackSize parameter and the maximum recursion depth and concurrency level are platform-dependent. On some platforms, the value of the stackSize parameter may have no effect whatsoever.

      The virtual machine is free to treat the stackSize parameter as a suggestion. If the specified value is unreasonably low for the platform, the virtual machine may instead use some platform-specific minimum value; if the specified value is unreasonably high, the virtual machine may instead use some platform-specific maximum. Likewise, the virtual machine is free to round the specified value up or down as it sees fit (or to ignore it completely).

      Specifying a value of zero for the stackSize parameter will cause this constructor to behave exactly like the Thread(ThreadGroup, Runnable, String) constructor.

      Due to the platform-dependent nature of the behavior of this constructor, extreme care should be exercised in its use. The thread stack size necessary to perform a given computation will likely vary from one JRE implementation to another. In light of this variation, careful tuning of the stack size parameter may be required, and the tuning may need to be repeated for each JRE implementation on which an application is to run.

      Implementation note: Java platform implementers are encouraged to document their implementation's behavior with respect to the stackSize parameter.

      For a non-null group, task, and name, invoking this constructor directly is equivalent to:

      Thread.ofPlatform().group(group).name(name).stackSize(stackSize).unstarted(task); 
      Parameters:
      group - the thread group. If null and there is a security manager, the group is determined by SecurityManager.getThreadGroup(). If there is not a security manager or SecurityManager.getThreadGroup() returns null, the group is set to the current thread's thread group.
      task - the object whose run method is invoked when this thread is started. If null, this thread's run method is invoked.
      name - the name of the new thread
      stackSize - the desired stack size for the new thread, or zero to indicate that this parameter is to be ignored.
      Throws:
      SecurityException - if the current thread cannot create a thread in the specified thread group
      Since:
      1.4
      See Also:
      Inheritance
    • Thread

      public Thread(ThreadGroup group, Runnable task, String name, long stackSize, boolean inheritInheritableThreadLocals)
      Allocates a new platform Thread so that it has task as its run object, has the specified name as its name, belongs to the thread group referred to by group, has the specified stackSize, and inherits initial values for inheritable thread-local variables if inheritThreadLocals is true.

      This constructor is identical to Thread(ThreadGroup,Runnable,String,long) with the added ability to suppress, or not, the inheriting of initial values for inheritable thread-local variables from the constructing thread. This allows for finer grain control over inheritable thread-locals. Care must be taken when passing a value of false for inheritThreadLocals, as it may lead to unexpected behavior if the new thread executes code that expects a specific thread-local value to be inherited.

      Specifying a value of true for the inheritThreadLocals parameter will cause this constructor to behave exactly like the Thread(ThreadGroup, Runnable, String, long) constructor.

      For a non-null group, task, and name, invoking this constructor directly is equivalent to:

      Thread.ofPlatform()
            .group(group)
            .name(name)
            .stackSize(stackSize)
            .inheritInheritableThreadLocals(inheritInheritableThreadLocals)
            .unstarted(task); 
      Parameters:
      group - the thread group. If null and there is a security manager, the group is determined by SecurityManager.getThreadGroup(). If there is not a security manager or SecurityManager.getThreadGroup() returns null, the group is set to the current thread's thread group.
      task - the object whose run method is invoked when this thread is started. If null, this thread's run method is invoked.
      name - the name of the new thread
      stackSize - the desired stack size for the new thread, or zero to indicate that this parameter is to be ignored
      inheritInheritableThreadLocals - if true, inherit initial values for inheritable thread-locals from the constructing thread, otherwise no initial values are inherited
      Throws:
      SecurityException - if the current thread cannot create a thread in the specified thread group
      Since:
      9
      See Also:
      Inheritance
  • Method Details

    • currentThread

      public static Thread currentThread()
      Returns the Thread object for the current thread.
      Returns:
      the current thread
    • yield

      public static void yield()
      A hint to the scheduler that the current thread is willing to yield its current use of a processor. The scheduler is free to ignore this hint.

      Yield is a heuristic attempt to improve relative progression between threads that would otherwise over-utilise a CPU. Its use should be combined with detailed profiling and benchmarking to ensure that it actually has the desired effect.

      It is rarely appropriate to use this method. It may be useful for debugging or testing purposes, where it may help to reproduce bugs due to race conditions. It may also be useful when designing concurrency control constructs such as the ones in the java.util.concurrent.locks package.

    • sleep

      public static void sleep(long millis) throws InterruptedException
      Causes the currently executing thread to sleep (temporarily cease execution) for the specified number of milliseconds, subject to the precision and accuracy of system timers and schedulers. The thread does not lose ownership of any monitors.
      Parameters:
      millis - the length of time to sleep in milliseconds
      Throws:
      IllegalArgumentException - if the value of millis is negative
      InterruptedException - if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.
    • sleep

      public static void sleep(long millis, int nanos) throws InterruptedException
      Causes the currently executing thread to sleep (temporarily cease execution) for the specified number of milliseconds plus the specified number of nanoseconds, subject to the precision and accuracy of system timers and schedulers. The thread does not lose ownership of any monitors.
      Parameters:
      millis - the length of time to sleep in milliseconds
      nanos - 0-999999 additional nanoseconds to sleep
      Throws:
      IllegalArgumentException - if the value of millis is negative, or the value of nanos is not in the range 0-999999
      InterruptedException - if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.
    • sleep

      public static void sleep(Duration duration) throws InterruptedException
      Causes the currently executing thread to sleep (temporarily cease execution) for the specified duration, subject to the precision and accuracy of system timers and schedulers. This method is a no-op if the duration is less than zero.
      Parameters:
      duration - the duration to sleep
      Throws:
      InterruptedException - if the current thread is interrupted while sleeping. The interrupted status of the current thread is cleared when this exception is thrown.
      NullPointerException - if duration is null
      Since:
      99
    • onSpinWait

      public static void onSpinWait()
      Indicates that the caller is momentarily unable to progress, until the occurrence of one or more actions on the part of other activities. By invoking this method within each iteration of a spin-wait loop construct, the calling thread indicates to the runtime that it is busy-waiting. The runtime may take action to improve the performance of invoking spin-wait loop constructions.
      API Note:
      As an example consider a method in a class that spins in a loop until some flag is set outside of that method. A call to the onSpinWait method should be placed inside the spin loop.
      
           class EventHandler {
               volatile boolean eventNotificationNotReceived;
               void waitForEventAndHandleIt() {
                   while ( eventNotificationNotReceived ) {
                       java.lang.Thread.onSpinWait();
                   }
                   readAndProcessEvent();
               }
      
               void readAndProcessEvent() {
                   // Read event from some source and process it
                    . . .
               }
           }
       

      The code above would remain correct even if the onSpinWait method was not called at all. However on some architectures the Java Virtual Machine may issue the processor instructions to address such code patterns in a more beneficial way.

      Since:
      9
    • ofPlatform

      public static Thread.Builder.OfPlatform ofPlatform()
      Returns a builder for creating a platform Thread or ThreadFactory that creates platform threads.
      API Note:
      The following are examples using the builder:
      
         // Start a daemon thread to run a task
         Thread thread = Thread.ofPlatform().daemon().start(runnable);
      
         // Create an unstarted thread with name "duke", its start() method
         // must be invoked to schedule it to execute.
         Thread thread = Thread.ofPlatform().name("duke").unstarted(runnable);
      
         // A ThreadFactory that creates daemon threads named "worker-0", "worker-1", ...
         ThreadFactory factory = Thread.ofPlatform().daemon().name("worker-", 0).factory();
       
      Returns:
      A builder for creating Thread or ThreadFactory objects.
      Since:
      99
    • ofVirtual

      public static Thread.Builder.OfVirtual ofVirtual()
      Returns a builder for creating a virtual Thread or ThreadFactory that creates virtual threads.
      API Note:
      The following are examples using the builder:
      
         // Start a virtual thread to run a task.
         Thread thread = Thread.ofVirtual().start(runnable);
      
         // A ThreadFactory that creates virtual threads
         ThreadFactory factory = Thread.ofVirtual().factory();
       
      Returns:
      A builder for creating Thread or ThreadFactory objects.
      Since:
      99
    • clone

      protected Object clone() throws CloneNotSupportedException
      Throws CloneNotSupportedException as a Thread can not be meaningfully cloned. Construct a new Thread instead.
      Overrides:
      clone in class Object
      Returns:
      a clone of this instance.
      Throws:
      CloneNotSupportedException - always
      See Also:
      Cloneable
    • startVirtualThread

      public static Thread startVirtualThread(Runnable task)
      Creates a virtual thread to execute a task and schedules it to execute.

      The thread has no permissions.

      This method is equivalent to:

      Thread.ofVirtual().start(task); 
      Parameters:
      task - the object to run when the thread executes
      Returns:
      a new, and started, virtual thread
      Since:
      99
      See Also:
      Inheritance
    • isVirtual

      public final boolean isVirtual()
      Returns true if this thread is a virtual thread. A virtual thread is scheduled by the Java virtual machine rather than the operating system.
      Returns:
      true if this thread is a virtual thread
      Since:
      99
    • start

      public void start()
      Schedules this thread to begin execution. The thread will execute independently of the current thread.

      It is never legal to start a thread more than once. In particular, a thread may not be restarted once it has completed execution.

      Throws:
      IllegalThreadStateException - if the thread was already started.
      RejectedExecutionException - if the thread is virtual and the scheduler cannot accept a task
    • run

      public void run()
      If this thread was constructed using a separate Runnable run object, then that Runnable object's run method is called; otherwise, this method does nothing and returns. This method does nothing when invoked on a virtual thread.

      Subclasses of Thread should override this method.

      Specified by:
      run in interface Runnable
      See Also:
      start(), Thread(ThreadGroup, Runnable, String)
    • stop

      @Deprecated(since="1.2", forRemoval=true) public final void stop()
      Deprecated, for removal: This API element is subject to removal in a future version.
      This method is inherently unsafe. Stopping a thread with Thread.stop causes it to unlock all of the monitors that it has locked (as a natural consequence of the unchecked ThreadDeath exception propagating up the stack). If any of the objects previously protected by these monitors were in an inconsistent state, the damaged objects become visible to other threads, potentially resulting in arbitrary behavior. Many uses of stop should be replaced by code that simply modifies some variable to indicate that the target thread should stop running. The target thread should check this variable regularly, and return from its run method in an orderly fashion if the variable indicates that it is to stop running. If the target thread waits for long periods (on a condition variable, for example), the interrupt method should be used to interrupt the wait. For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?.
      Forces the thread to stop executing.

      If there is a security manager installed, its checkAccess method is called with this as its argument. This may result in a SecurityException being raised (in the current thread).

      If this thread is different from the current thread (that is, the current thread is trying to stop a thread other than itself), the security manager's checkPermission method (with a RuntimePermission("stopThread") argument) is called in addition. Again, this may result in throwing a SecurityException (in the current thread).

      The thread represented by this thread is forced to stop whatever it is doing abnormally and to throw a newly created ThreadDeath object as an exception.

      It is permitted to stop a thread that has not yet been started. If the thread is eventually started, it immediately terminates.

      An application should not normally try to catch ThreadDeath unless it must do some extraordinary cleanup operation (note that the throwing of ThreadDeath causes finally clauses of try statements to be executed before the thread officially terminates). If a catch clause catches a ThreadDeath object, it is important to rethrow the object so that the thread actually terminates.

      The top-level error handler that reacts to otherwise uncaught exceptions does not print out a message or otherwise notify the application if the uncaught exception is an instance of ThreadDeath.

      Throws:
      SecurityException - if the current thread cannot modify this thread.
      UnsupportedOperationException - if invoked on a virtual thread
      See Also:
      interrupt(), checkAccess(), run(), start(), ThreadDeath, ThreadGroup.uncaughtException(Thread,Throwable), SecurityManager.checkAccess(Thread), SecurityManager.checkPermission(java.security.Permission)
    • interrupt

      public void interrupt()
      Interrupts this thread.

      Unless the current thread is interrupting itself, which is always permitted, the checkAccess method of this thread is invoked, which may cause a SecurityException to be thrown.

      If this thread is blocked in an invocation of the wait(), wait(long), or wait(long, int) methods of the Object class, or of the join(), join(long), join(long, int), sleep(long), or sleep(long, int) methods of this class, then its interrupt status will be cleared and it will receive an InterruptedException.

      If this thread is blocked in an I/O operation upon an InterruptibleChannel then the channel will be closed, the thread's interrupt status will be set, and the thread will receive a ClosedByInterruptException.

      If this thread is blocked in a Selector then the thread's interrupt status will be set and it will return immediately from the selection operation, possibly with a non-zero value, just as if the selector's wakeup method were invoked.

      If none of the previous conditions hold then this thread's interrupt status will be set.

      Interrupting a thread that is not alive need not have any effect.

      Implementation Note:
      In the JDK Reference Implementation, interruption of a thread that is not alive still records that the interrupt request was made and will report it via interrupted and isInterrupted().
      Throws:
      SecurityException - if the current thread cannot modify this thread
    • interrupted

      public static boolean interrupted()
      Tests whether the current thread has been interrupted. The interrupted status of the thread is cleared by this method. In other words, if this method were to be called twice in succession, the second call would return false (unless the current thread were interrupted again, after the first call had cleared its interrupted status and before the second call had examined it).
      Returns:
      true if the current thread has been interrupted; false otherwise.
      See Also:
      isInterrupted()
    • isInterrupted

      public boolean isInterrupted()
      Tests whether this thread has been interrupted. The interrupted status of the thread is unaffected by this method.
      Returns:
      true if this thread has been interrupted; false otherwise.
      See Also:
      interrupted()
    • isAlive

      public final boolean isAlive()
      Tests if this thread is alive. A thread is alive if it has been started and has not yet terminated.
      Returns:
      true if this thread is alive; false otherwise.
    • suspend

      @Deprecated(since="1.2", forRemoval=true) public final void suspend()
      Deprecated, for removal: This API element is subject to removal in a future version.
      This method has been deprecated, as it is inherently deadlock-prone. If the target thread holds a lock on the monitor protecting a critical system resource when it is suspended, no thread can access this resource until the target thread is resumed. If the thread that would resume the target thread attempts to lock this monitor prior to calling resume, deadlock results. Such deadlocks typically manifest themselves as "frozen" processes. For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?.
      Suspends this thread.

      First, the checkAccess method of this thread is called with no arguments. This may result in throwing a SecurityException (in the current thread).

      If the thread is alive, it is suspended and makes no further progress unless and until it is resumed.

      Throws:
      SecurityException - if the current thread cannot modify this thread.
      UnsupportedOperationException - if invoked on a virtual thread
      See Also:
      checkAccess()
    • resume

      @Deprecated(since="1.2", forRemoval=true) public final void resume()
      Deprecated, for removal: This API element is subject to removal in a future version.
      This method exists solely for use with suspend(), which has been deprecated because it is deadlock-prone. For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?.
      Resumes a suspended thread.

      First, the checkAccess method of this thread is called with no arguments. This may result in throwing a SecurityException (in the current thread).

      If the thread is alive but suspended, it is resumed and is permitted to make progress in its execution.

      Throws:
      SecurityException - if the current thread cannot modify this thread.
      UnsupportedOperationException - if invoked on a virtual thread
      See Also:
      checkAccess(), suspend()
    • setPriority

      public final void setPriority(int newPriority)
      Changes the priority of this thread.

      First the checkAccess method of this thread is called with no arguments. This may result in throwing a SecurityException.

      The priority of virtual-threads is always NORM_PRIORITY and is not changed by this method. Otherwise, the priority of this thread is set to the smaller of the specified newPriority and the maximum permitted priority of the thread's thread group.

      Parameters:
      newPriority - priority to set this thread to
      Throws:
      IllegalArgumentException - If the priority is not in the range MIN_PRIORITY to MAX_PRIORITY.
      SecurityException - if the current thread cannot modify this thread.
      See Also:
      getPriority(), checkAccess(), getThreadGroup(), MAX_PRIORITY, MIN_PRIORITY, ThreadGroup.getMaxPriority()
    • getPriority

      public final int getPriority()
      Returns this thread's priority. The priority of a virtual thread is always NORM_PRIORITY.
      Returns:
      this thread's priority.
      See Also:
      setPriority(int)
    • setName

      public final void setName(String name)
      Changes the name of this thread to be equal to the argument name.

      First the checkAccess method of this thread is called with no arguments. This may result in throwing a SecurityException.

      Implementation Note:
      If this thread is the current thread, and is a platform thread that isn't mapped to a native thread attached to the VM with the Java Native Interface AttachCurrentThread function, then a best effort attempt is made to change the operating system thread name too.
      Parameters:
      name - the new name for this thread.
      Throws:
      SecurityException - if the current thread cannot modify this thread.
      See Also:
      getName(), checkAccess()
    • getName

      public final String getName()
      Returns this thread's name.
      Returns:
      this thread's name.
      See Also:
      setName(String)
    • getThreadGroup

      public final ThreadGroup getThreadGroup()
      Returns the thread group to which this thread belongs. This method returns null if the thread has terminated.
      Returns:
      this thread's thread group.
    • activeCount

      @Deprecated(since="99") public static int activeCount()
      Deprecated.
      This method is obsolete. Code that needs an estimate of the number of active platform threads in a thread group can invoke the thread group's ThreadGroup.activeCount() method.
      Returns an estimate of the number of active threads in the current thread's thread group and its subgroups. Virtual threads are not considered active threads in a thread group so this method does not include virtual threads in the estimate.

      The value returned is only an estimate because the number of threads may change dynamically while this method traverses internal data structures, and might be affected by the presence of certain system threads. This method is intended primarily for debugging and monitoring purposes.

      Returns:
      an estimate of the number of active threads in the current thread's thread group and in any other thread group that has the current thread's thread group as an ancestor
    • enumerate

      @Deprecated(since="99") public static int enumerate(Thread[] tarray)
      Deprecated.
      This method is obsolete. Code that needs to enumerate the active platform threads can invoke the thread group's ThreadGroup.enumerate(Thread[]) method.
      Copies into the specified array every active thread in the current thread's thread group and its subgroups. This method simply invokes the ThreadGroup.enumerate(Thread[]) method of the current thread's thread group. Virtual threads are not considered active threads in a thread group so this method does not enumerate virtual threads.

      An application might use the activeCount method to get an estimate of how big the array should be, however if the array is too short to hold all the threads, the extra threads are silently ignored. If it is critical to obtain every active thread in the current thread's thread group and its subgroups, the invoker should verify that the returned int value is strictly less than the length of tarray.

      Due to the inherent race condition in this method, it is recommended that the method only be used for debugging and monitoring purposes.

      Parameters:
      tarray - an array into which to put the list of threads
      Returns:
      the number of threads put into the array
      Throws:
      SecurityException - if ThreadGroup.checkAccess() determines that the current thread cannot access its thread group
    • countStackFrames

      @Deprecated(since="1.2", forRemoval=true) public int countStackFrames()
      Deprecated, for removal: This API element is subject to removal in a future version.
      This method was originally designed to count the number of stack frames but the results were never well-defined and it depended on thread-suspension. This method is subject to removal in a future version of Java SE.
      Throws UnsupportedOperationException.
      Returns:
      nothing
      See Also:
      StackWalker
    • join

      public final void join(long millis) throws InterruptedException
      Waits at most millis milliseconds for this thread to terminate. A timeout of 0 means to wait forever. This method returns immediately, without waiting, if the thread has not been started.
      Implementation Note:
      For platform threads, the implementation uses a loop of this.wait calls conditioned on this.isAlive. As a thread terminates the this.notifyAll method is invoked. It is recommended that applications not use wait, notify, or notifyAll on Thread instances.
      Parameters:
      millis - the time to wait in milliseconds
      Throws:
      IllegalArgumentException - if the value of millis is negative
      InterruptedException - if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.
    • join

      public final void join(long millis, int nanos) throws InterruptedException
      Waits at most millis milliseconds plus nanos nanoseconds for this thread to terminate. If both arguments are 0, it means to wait forever. This method returns immediately, without waiting, if the thread has not been started.
      Implementation Note:
      For platform threads, the implementation uses a loop of this.wait calls conditioned on this.isAlive. As a thread terminates the this.notifyAll method is invoked. It is recommended that applications not use wait, notify, or notifyAll on Thread instances.
      Parameters:
      millis - the time to wait in milliseconds
      nanos - 0-999999 additional nanoseconds to wait
      Throws:
      IllegalArgumentException - if the value of millis is negative, or the value of nanos is not in the range 0-999999
      InterruptedException - if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.
    • join

      public final void join() throws InterruptedException
      Waits for this thread to terminate.

      An invocation of this method behaves in exactly the same way as the invocation

      join(0)
      Throws:
      InterruptedException - if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.
    • join

      public final boolean join(Duration duration) throws InterruptedException
      Waits for this thread to terminate for up to the given waiting duration.

      This method does not wait if the duration to wait is less than or equal to zero. In this case, the method just tests if the thread has terminated.

      Parameters:
      duration - the maximum duration to wait
      Returns:
      true if the thread has terminated, false if the thread has not terminated
      Throws:
      InterruptedException - if the current thread is interrupted while waiting. The interrupted status of the current thread is cleared when this exception is thrown.
      IllegalThreadStateException - if this thread has not been started.
      Since:
      99
    • dumpStack

      public static void dumpStack()
      Prints a stack trace of the current thread to the standard error stream. This method is useful for debugging.
    • setDaemon

      public final void setDaemon(boolean on)
      Marks this thread as either a daemon thread or a user thread. The daemon status of a virtual thread is meaningless and is not changed by this method (the isDaemon method always returns true). The Java Virtual Machine exits when the only threads running are all daemon threads.

      This method must be invoked before the thread is started.

      Parameters:
      on - if true, marks this thread as a daemon thread
      Throws:
      IllegalThreadStateException - if this thread is alive
      SecurityException - if checkAccess() determines that the current thread cannot modify this thread
    • isDaemon

      public final boolean isDaemon()
      Tests if this thread is a daemon thread. The daemon status of a virtual thread is meaningless, this method returns true if this is a virtual thread.
      Returns:
      true if this thread is a daemon thread; false otherwise.
      See Also:
      setDaemon(boolean)
    • checkAccess

      public final void checkAccess()
      Determines if the currently running thread has permission to modify this thread.

      If there is a security manager, its checkAccess method is called with this thread as its argument. This may result in throwing a SecurityException.

      Throws:
      SecurityException - if the current thread is not allowed to access this thread.
      See Also:
      SecurityManager.checkAccess(Thread)
    • toString

      public String toString()
      Returns a string representation of this thread. The string representation will usually include the thread's name. The default implementation for platform threads includes the thread's name, priority, and the name of the thread group.
      Overrides:
      toString in class Object
      Returns:
      a string representation of this thread.
    • getContextClassLoader

      public ClassLoader getContextClassLoader()
      Returns the context ClassLoader for this thread. The context ClassLoader may be set by the creator of the thread for use by code running in this thread when loading classes and resources. If not set, the default is to inherit the context class loader from the parent thread.

      The context ClassLoader of the primordial thread is typically set to the class loader used to load the application.

      Returns:
      the context ClassLoader for this thread, or null indicating the system class loader (or, failing that, the bootstrap class loader)
      Throws:
      SecurityException - if a security manager is present, and the caller's class loader is not null and is not the same as or an ancestor of the context class loader, and the caller does not have the RuntimePermission("getClassLoader")
      Since:
      1.2
    • setContextClassLoader

      public void setContextClassLoader(ClassLoader cl)
      Sets the context ClassLoader for this thread. The context ClassLoader may be set by the creator of the thread for use by code running in this thread when loading classes and resources.

      If a security manager is present, its checkPermission method is invoked with a RuntimePermission ("setContextClassLoader") permission to see if setting the context ClassLoader is permitted.

      Parameters:
      cl - the context ClassLoader for this Thread, or null indicating the system class loader (or, failing that, the bootstrap class loader)
      Throws:
      UnsupportedOperationException - if this thread is not allowed to set values for its copy of thread-local variables
      SecurityException - if the current thread cannot set the context ClassLoader
      Since:
      1.2
    • holdsLock

      public static boolean holdsLock(Object obj)
      Returns true if and only if the current thread holds the monitor lock on the specified object.

      This method is designed to allow a program to assert that the current thread already holds a specified lock:

           assert Thread.holdsLock(obj);
       
      Parameters:
      obj - the object on which to test lock ownership
      Returns:
      true if the current thread holds the monitor lock on the specified object.
      Throws:
      NullPointerException - if obj is null
      Since:
      1.4
    • getStackTrace

      public StackTraceElement[] getStackTrace()
      Returns an array of stack trace elements representing the stack dump of this thread. This method will return a zero-length array if this thread has not started, has started but has not yet been scheduled to run by the system, or has terminated. If the returned array is of non-zero length then the first element of the array represents the top of the stack, which is the most recent method invocation in the sequence. The last element of the array represents the bottom of the stack, which is the least recent method invocation in the sequence.

      If there is a security manager, and this thread is not the current thread, then the security manager's checkPermission method is called with a RuntimePermission("getStackTrace") permission to see if it's ok to get the stack trace.

      Some virtual machines may, under some circumstances, omit one or more stack frames from the stack trace. In the extreme case, a virtual machine that has no stack trace information concerning this thread is permitted to return a zero-length array from this method.

      Returns:
      an array of StackTraceElement, each represents one stack frame.
      Throws:
      SecurityException - if a security manager exists and its checkPermission method doesn't allow getting the stack trace of thread.
      Since:
      1.5
      See Also:
      SecurityManager.checkPermission(java.security.Permission), RuntimePermission, Throwable.getStackTrace()
    • getAllStackTraces

      public static Map<Thread,​StackTraceElement[]> getAllStackTraces()
      Returns a map of stack traces for all live threads that are scheduled by the operating system. The map does not include virtual threads. The map keys are threads and each map value is an array of StackTraceElement that represents the stack dump of the corresponding Thread. The returned stack traces are in the format specified for the getStackTrace method.

      The threads may be executing while this method is called. The stack trace of each thread only represents a snapshot and each stack trace may be obtained at different time. A zero-length array will be returned in the map value if the virtual machine has no stack trace information about a thread.

      If there is a security manager, then the security manager's checkPermission method is called with a RuntimePermission("getStackTrace") permission as well as RuntimePermission("modifyThreadGroup") permission to see if it is ok to get the stack trace of all threads.

      Returns:
      a Map from Thread to an array of StackTraceElement that represents the stack trace of the corresponding thread.
      Throws:
      SecurityException - if a security manager exists and its checkPermission method doesn't allow getting the stack trace of thread.
      Since:
      1.5
      See Also:
      getStackTrace(), SecurityManager.checkPermission(java.security.Permission), RuntimePermission, Throwable.getStackTrace()
    • getId

      public long getId()
      Returns the identifier of this Thread. The thread ID is a positive long number generated when this thread was created. The thread ID is unique and remains unchanged during its lifetime. When a thread is terminated, this thread ID may be reused.
      Returns:
      this thread's ID.
      Since:
      1.5
    • getState

      public Thread.State getState()
      Returns the state of this thread. This method is designed for use in monitoring of the system state, not for synchronization control.
      Returns:
      this thread's state.
      Since:
      1.5
    • setDefaultUncaughtExceptionHandler

      public static void setDefaultUncaughtExceptionHandler(Thread.UncaughtExceptionHandler eh)
      Set the default handler invoked when a thread abruptly terminates due to an uncaught exception, and no other handler has been defined for that thread.

      Uncaught exception handling is controlled first by the thread, then by the thread's ThreadGroup object and finally by the default uncaught exception handler. If the thread does not have an explicit uncaught exception handler set, and the thread's thread group (including parent thread groups) does not specialize its uncaughtException method, then the default handler's uncaughtException method will be invoked.

      By setting the default uncaught exception handler, an application can change the way in which uncaught exceptions are handled (such as logging to a specific device, or file) for those threads that would already accept whatever "default" behavior the system provided.

      Note that the default uncaught exception handler should not usually defer to the thread's ThreadGroup object, as that could cause infinite recursion.

      Parameters:
      eh - the object to use as the default uncaught exception handler. If null then there is no default handler.
      Throws:
      SecurityException - if a security manager is present and it denies RuntimePermission("setDefaultUncaughtExceptionHandler")
      Since:
      1.5
      See Also:
      setUncaughtExceptionHandler(java.lang.Thread.UncaughtExceptionHandler), getUncaughtExceptionHandler(), ThreadGroup.uncaughtException(java.lang.Thread, java.lang.Throwable)
    • getDefaultUncaughtExceptionHandler

      public static Thread.UncaughtExceptionHandler getDefaultUncaughtExceptionHandler()
      Returns the default handler invoked when a thread abruptly terminates due to an uncaught exception. If the returned value is null, there is no default.
      Returns:
      the default uncaught exception handler for all threads
      Since:
      1.5
      See Also:
      setDefaultUncaughtExceptionHandler(java.lang.Thread.UncaughtExceptionHandler)
    • getUncaughtExceptionHandler

      public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler()
      Returns the handler invoked when this thread abruptly terminates due to an uncaught exception. If this thread has not had an uncaught exception handler explicitly set then this thread's ThreadGroup object is returned, unless this thread has terminated, in which case null is returned.
      Returns:
      the uncaught exception handler for this thread
      Since:
      1.5
    • setUncaughtExceptionHandler

      public void setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler eh)
      Set the handler invoked when this thread abruptly terminates due to an uncaught exception.

      A thread can take full control of how it responds to uncaught exceptions by having its uncaught exception handler explicitly set. If no such handler is set then the thread's ThreadGroup object acts as its handler.

      Parameters:
      eh - the object to use as this thread's uncaught exception handler. If null then this thread has no explicit handler.
      Throws:
      SecurityException - if the current thread is not allowed to modify this thread.
      Since:
      1.5
      See Also:
      setDefaultUncaughtExceptionHandler(java.lang.Thread.UncaughtExceptionHandler), ThreadGroup.uncaughtException(java.lang.Thread, java.lang.Throwable)