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.Every thread has a priority. Threads with higher priority are executed in preference to threads with lower priority. Each thread may or may not also be marked as a daemon. When code running in some thread creates a new
Thread
object, the new thread has its priority initially set equal to the priority of the creating thread, and is a daemon thread if and only if the creating thread is a daemon.When a Java Virtual Machine starts up, there is usually a single non-daemon thread (which typically calls the method named
main
of some designated class). The Java Virtual Machine continues to execute threads until either of the following occurs:- The
exit
method of classRuntime
has been called and the security manager has permitted the exit operation to take place. - All threads that are not daemon threads have died, either by returning from the call to the
run
method or by throwing an exception that propagates beyond therun
method.
There are two ways to create a new thread of execution. One is to declare a class to be a subclass of
Thread
. This subclass should override therun
method of classThread
. An instance of the subclass can then be allocated and started. For example, a thread that computes primes larger than a stated value could be written as follows:
class PrimeThread extends Thread { long minPrime; PrimeThread(long minPrime) { this.minPrime = minPrime; } public void run() { // compute primes larger than minPrime . . . } }
The following code would then create a thread and start it running:
PrimeThread p = new PrimeThread(143); p.start();
The other way to create a thread is to declare a class that implements the
Runnable
interface. That class then implements therun
method. An instance of the class can then be allocated, passed as an argument when creatingThread
, and started. The same example in this other style looks like the following:
class PrimeRun implements Runnable { long minPrime; PrimeRun(long minPrime) { this.minPrime = minPrime; } public void run() { // compute primes larger than minPrime . . . } }
The following code would then create a thread and start it running:
PrimeRun p = new PrimeRun(143); new Thread(p).start();
Every thread has a name for identification purposes. More than one thread may have the same name. If a name is not specified when a thread is created, a new name is generated for it.
Unless otherwise noted, passing a
null
argument to a constructor or method in this class will cause aNullPointerException
to be thrown.- Since:
- JDK1.0
- See Also:
-
Runnable
,Runtime.exit(int)
,run()
,stop()
-
-
Nested Class Summary
Nested Classes Modifier and Type Class and Description static class
Thread.State
A thread state.static interface
Thread.UncaughtExceptionHandler
Interface for handlers invoked when a Thread abruptly terminates due to an uncaught exception.
-
Field Summary
Fields Modifier and Type Field and Description static int
MAX_PRIORITY
The maximum priority that a thread can have.static int
MIN_PRIORITY
The minimum priority that a thread can have.static int
NORM_PRIORITY
The default priority that is assigned to a thread.
-
Constructor Summary
Constructors Constructor and Description Thread()
Allocates a newThread
object.Thread(Runnable target)
Allocates a newThread
object.Thread(Runnable target, String name)
Allocates a newThread
object.Thread(String name)
Allocates a newThread
object.Thread(ThreadGroup group, Runnable target)
Allocates a newThread
object.Thread(ThreadGroup group, Runnable target, String name)
Allocates a newThread
object so that it hastarget
as its run object, has the specifiedname
as its name, and belongs to the thread group referred to bygroup
.Thread(ThreadGroup group, Runnable target, String name, long stackSize)
Allocates a newThread
object so that it hastarget
as its run object, has the specifiedname
as its name, and belongs to the thread group referred to bygroup
, and has the specified stack size.Thread(ThreadGroup group, String name)
Allocates a newThread
object.
-
Method Summary
All Methods Static Methods Instance Methods Concrete Methods Deprecated Methods Modifier and Type Method and Description static int
activeCount()
Returns an estimate of the number of active threads in the current thread's thread group and its subgroups.void
checkAccess()
Determines if the currently running thread has permission to modify this thread.protected Object
clone()
Throws CloneNotSupportedException as a Thread can not be meaningfully cloned.int
countStackFrames()
Deprecated.The definition of this call depends onsuspend()
, which is deprecated. Further, the results of this call were never well-defined.static Thread
currentThread()
Returns a reference to the currently executing thread object.void
destroy()
Deprecated.This method was originally designed to destroy this thread without any cleanup. Any monitors it held would have remained locked. However, the method was never implemented. If if were to be implemented, it would be deadlock-prone in much the manner ofsuspend()
. If the target thread held a lock protecting a critical system resource when it was destroyed, no thread could ever access this resource again. If another thread ever attempted to lock this resource, deadlock would result. Such deadlocks typically manifest themselves as "frozen" processes. For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?.static void
dumpStack()
Prints a stack trace of the current thread to the standard error stream.static int
enumerate(Thread[] tarray)
Copies into the specified array every active thread in the current thread's thread group and its subgroups.static Map<Thread,StackTraceElement[]>
getAllStackTraces()
Returns a map of stack traces for all live threads.ClassLoader
getContextClassLoader()
Returns the context ClassLoader for this Thread.static Thread.UncaughtExceptionHandler
getDefaultUncaughtExceptionHandler()
Returns the default handler invoked when a thread abruptly terminates due to an uncaught exception.long
getId()
Returns the identifier of this Thread.String
getName()
Returns this thread's name.int
getPriority()
Returns this thread's priority.StackTraceElement[]
getStackTrace()
Returns an array of stack trace elements representing the stack dump of this thread.Thread.State
getState()
Returns the state of this thread.ThreadGroup
getThreadGroup()
Returns the thread group to which this thread belongs.Thread.UncaughtExceptionHandler
getUncaughtExceptionHandler()
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
interrupt()
Interrupts this thread.static boolean
interrupted()
Tests whether the current thread has been interrupted.boolean
isAlive()
Tests if this thread is alive.boolean
isDaemon()
Tests if this thread is a daemon thread.boolean
isInterrupted()
Tests whether this thread has been interrupted.void
join()
Waits for this thread to die.void
join(long millis)
Waits at mostmillis
milliseconds for this thread to die.void
join(long millis, int nanos)
Waits at mostmillis
milliseconds plusnanos
nanoseconds for this thread to die.void
resume()
Deprecated.This method exists solely for use withsuspend()
, which has been deprecated because it is deadlock-prone. For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?.void
run()
If this thread was constructed using a separateRunnable
run object, then thatRunnable
object'srun
method is called; otherwise, this method does nothing and returns.void
setContextClassLoader(ClassLoader cl)
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
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.void
setName(String name)
Changes the name of this thread to be equal to the argumentname
.void
setPriority(int newPriority)
Changes the priority of this thread.void
setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler eh)
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.void
start()
Causes this thread to begin execution; the Java Virtual Machine calls therun
method of this thread.void
stop()
Deprecated.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 uncheckedThreadDeath
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 ofstop
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), theinterrupt
method should be used to interrupt the wait. For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?.void
stop(Throwable obj)
Deprecated.This method was originally designed to force a thread to stop and throw a givenThrowable
as an exception. It was inherently unsafe (seestop()
for details), and furthermore could be used to generate exceptions that the target thread was not prepared to handle. For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?.void
suspend()
Deprecated.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 callingresume
, deadlock results. Such deadlocks typically manifest themselves as "frozen" processes. For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?.String
toString()
Returns a string representation of this thread, including the thread's name, priority, and thread group.static void
yield()
A hint to the scheduler that the current thread is willing to yield its current use of a processor.
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-
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Field Detail
MIN_PRIORITY
public static final int MIN_PRIORITY
The minimum priority that a 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 thread can have.- See Also:
- Constant Field Values
-
Constructor Detail
Thread
public Thread()
Allocates a newThread
object. This constructor has the same effect as Thread(null, null, gname)
, wheregname
is a newly generated name. Automatically generated names are of the form"Thread-"+
n, where n is an integer.
Thread
public Thread(Runnable target)
Allocates a newThread
object. This constructor has the same effect as Thread(null, target, gname)
, wheregname
is a newly generated name. Automatically generated names are of the form"Thread-"+
n, where n is an integer.- Parameters:
-
target
- the object whoserun
method is invoked when this thread is started. Ifnull
, this classesrun
method does nothing.
Thread
public Thread(ThreadGroup group, Runnable target)
Allocates a newThread
object. This constructor has the same effect as Thread(group, target, gname)
,wheregname
is a newly generated name. Automatically generated names are of the form"Thread-"+
n, where n is an integer.- Parameters:
-
group
- the thread group. Ifnull
and there is a security manager, the group is determined by SecurityManager.getThreadGroup(). If there is not a security manager orSecurityManager.getThreadGroup()
returnsnull
, the group is set to the current thread's thread group. -
target
- the object whoserun
method is invoked when this thread is started. Ifnull
, this thread's run method is invoked. - Throws:
-
SecurityException
- if the current thread cannot create a thread in the specified thread group
Thread
public Thread(String name)
- Parameters:
-
name
- the name of the new thread
Thread
public Thread(ThreadGroup group, String name)
- Parameters:
-
group
- the thread group. Ifnull
and there is a security manager, the group is determined by SecurityManager.getThreadGroup(). If there is not a security manager orSecurityManager.getThreadGroup()
returnsnull
, 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
Thread
public Thread(Runnable target, String name)
- Parameters:
-
target
- the object whoserun
method is invoked when this thread is started. Ifnull
, this thread's run method is invoked. -
name
- the name of the new thread
Thread
public Thread(ThreadGroup group, Runnable target, String name)
Allocates a newThread
object so that it hastarget
as its run object, has the specifiedname
as its name, and belongs to the thread group referred to bygroup
.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 theRuntimePermission("enableContextClassLoaderOverride")
permission when invoked directly or indirectly by the constructor of a subclass which overrides thegetContextClassLoader
orsetContextClassLoader
methods.The priority of the newly created thread is set equal to the priority of the thread creating it, that is, the currently running thread. 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.
- Parameters:
-
group
- the thread group. Ifnull
and there is a security manager, the group is determined by SecurityManager.getThreadGroup(). If there is not a security manager orSecurityManager.getThreadGroup()
returnsnull
, the group is set to the current thread's thread group. -
target
- the object whoserun
method is invoked when this thread is started. Ifnull
, 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.
Thread
public Thread(ThreadGroup group, Runnable target, String name, long stackSize)
Allocates a newThread
object so that it hastarget
as its run object, has the specifiedname
as its name, and belongs to the thread group referred to bygroup
, 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 thestackSize
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 aStackOverflowError
. Similarly, specifying a lower value may allow a greater number of threads to exist concurrently without throwing anOutOfMemoryError
(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 thestackSize
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 theThread(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.- Parameters:
-
group
- the thread group. Ifnull
and there is a security manager, the group is determined by SecurityManager.getThreadGroup(). If there is not a security manager orSecurityManager.getThreadGroup()
returnsnull
, the group is set to the current thread's thread group. -
target
- the object whoserun
method is invoked when this thread is started. Ifnull
, 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
-
Method Detail
currentThread
public static Thread currentThread()
Returns a reference to the currently executing thread object.- Returns:
- the currently executing 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 ofmillis
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 ofmillis
is negative, or the value ofnanos
is not in the range0-999999
-
InterruptedException
- if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.
clone
protected Object clone() throws CloneNotSupportedException
Throws CloneNotSupportedException as a Thread can not be meaningfully cloned. Construct a new Thread instead.- Overrides:
-
clone
in classObject
- Returns:
- a clone of this instance.
- Throws:
-
CloneNotSupportedException
- always - See Also:
-
Cloneable
start
public void start()
Causes this thread to begin execution; the Java Virtual Machine calls therun
method of this thread.The result is that two threads are running concurrently: the current thread (which returns from the call to the
start
method) and the other thread (which executes itsrun
method).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. - See Also:
-
run()
,stop()
run
public void run()
If this thread was constructed using a separateRunnable
run object, then thatRunnable
object'srun
method is called; otherwise, this method does nothing and returns.Subclasses of
Thread
should override this method.- Specified by:
-
run
in interfaceRunnable
- See Also:
-
start()
,stop()
,Thread(ThreadGroup, Runnable, String)
stop
@Deprecated public final void stop()
Deprecated. 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 uncheckedThreadDeath
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 ofstop
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), theinterrupt
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 withthis
as its argument. This may result in aSecurityException
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 aRuntimePermission("stopThread")
argument) is called in addition. Again, this may result in throwing aSecurityException
(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 ofThreadDeath
causesfinally
clauses oftry
statements to be executed before the thread officially dies). If acatch
clause catches aThreadDeath
object, it is important to rethrow the object so that the thread actually dies.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. - See Also:
-
interrupt()
,checkAccess()
,run()
,start()
,ThreadDeath
,ThreadGroup.uncaughtException(Thread,Throwable)
,SecurityManager.checkAccess(Thread)
,SecurityManager.checkPermission(java.security.Permission)
stop
@Deprecated public final void stop(Throwable obj)
Deprecated. This method was originally designed to force a thread to stop and throw a givenThrowable
as an exception. It was inherently unsafe (seestop()
for details), and furthermore could be used to generate exceptions that the target thread was not prepared to handle. For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?.ThrowsUnsupportedOperationException
.- Parameters:
-
obj
- ignored
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 aSecurityException
to be thrown.If this thread is blocked in an invocation of the
wait()
,wait(long)
, orwait(long, int)
methods of theObject
class, or of thejoin()
,join(long)
,join(long, int)
,sleep(long)
, orsleep(long, int)
, methods of this class, then its interrupt status will be cleared and it will receive anInterruptedException
.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 aClosedByInterruptException
.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'swakeup
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.
- 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).A thread interruption ignored because a thread was not alive at the time of the interrupt will be reflected by this method returning false.
- 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.A thread interruption ignored because a thread was not alive at the time of the interrupt will be reflected by this method returning false.
- Returns:
-
true
if this thread has been interrupted;false
otherwise. - See Also:
-
interrupted()
destroy
@Deprecated public void destroy()
Deprecated. This method was originally designed to destroy this thread without any cleanup. Any monitors it held would have remained locked. However, the method was never implemented. If if were to be implemented, it would be deadlock-prone in much the manner ofsuspend()
. If the target thread held a lock protecting a critical system resource when it was destroyed, no thread could ever access this resource again. If another thread ever attempted to lock this resource, deadlock would result. Such deadlocks typically manifest themselves as "frozen" processes. For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?.ThrowsNoSuchMethodError
.- Throws:
-
NoSuchMethodError
- always
isAlive
public final boolean isAlive()
Tests if this thread is alive. A thread is alive if it has been started and has not yet died.- Returns:
-
true
if this thread is alive;false
otherwise.
suspend
@Deprecated public final void suspend()
Deprecated. 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 callingresume
, 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 aSecurityException
(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. - See Also:
-
checkAccess()
resume
@Deprecated public final void resume()
Deprecated. This method exists solely for use withsuspend()
, 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 aSecurityException
(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. - 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 aSecurityException
.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 rangeMIN_PRIORITY
toMAX_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.- 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 argumentname
.First the
checkAccess
method of this thread is called with no arguments. This may result in throwing aSecurityException
.- 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 this thread has died (been stopped).- Returns:
- this thread's thread group.
activeCount
public static int activeCount()
Returns an estimate of the number of active threads in the current thread's thread group and its subgroups. Recursively iterates over all subgroups in the current thread's thread group.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
public static int enumerate(Thread[] tarray)
Copies into the specified array every active thread in the current thread's thread group and its subgroups. This method simply invokes theThreadGroup.enumerate(Thread[])
method of the current thread's thread group.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
- ifThreadGroup.checkAccess()
determines that the current thread cannot access its thread group
countStackFrames
@Deprecated public int countStackFrames()
Deprecated. The definition of this call depends onsuspend()
, which is deprecated. Further, the results of this call were never well-defined.Counts the number of stack frames in this thread. The thread must be suspended.- Returns:
- the number of stack frames in this thread.
- Throws:
-
IllegalThreadStateException
- if this thread is not suspended.
join
public final void join(long millis) throws InterruptedException
Waits at mostmillis
milliseconds for this thread to die. A timeout of0
means to wait forever.This implementation uses a loop of
this.wait
calls conditioned onthis.isAlive
. As a thread terminates thethis.notifyAll
method is invoked. It is recommended that applications not usewait
,notify
, ornotifyAll
onThread
instances.- Parameters:
-
millis
- the time to wait in milliseconds - Throws:
-
IllegalArgumentException
- if the value ofmillis
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 mostmillis
milliseconds plusnanos
nanoseconds for this thread to die.This implementation uses a loop of
this.wait
calls conditioned onthis.isAlive
. As a thread terminates thethis.notifyAll
method is invoked. It is recommended that applications not usewait
,notify
, ornotifyAll
onThread
instances.- Parameters:
-
millis
- the time to wait in milliseconds -
nanos
-0-999999
additional nanoseconds to wait - Throws:
-
IllegalArgumentException
- if the value ofmillis
is negative, or the value ofnanos
is not in the range0-999999
-
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 die.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.
dumpStack
public static void dumpStack()
Prints a stack trace of the current thread to the standard error stream. This method is used only for debugging.- See Also:
-
Throwable.printStackTrace()
setDaemon
public final void setDaemon(boolean on)
Marks this thread as either a daemon thread or a user thread. 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
- iftrue
, marks this thread as a daemon thread - Throws:
-
IllegalThreadStateException
- if this thread is alive -
SecurityException
- ifcheckAccess()
determines that the current thread cannot modify this thread
isDaemon
public final boolean isDaemon()
Tests if this thread is a daemon 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 aSecurityException
.- 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, including the thread's name, priority, and thread group.
getContextClassLoader
public ClassLoader getContextClassLoader()
Returns the context ClassLoader for this Thread. The context ClassLoader is provided 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 the ClassLoader context of the parent Thread. The context ClassLoader of the primordial thread is typically set to the class loader used to load the application.If a security manager is present, and the invoker's class loader is not
null
and is not the same as or an ancestor of the context class loader, then this method invokes the security manager'scheckPermission
method with aRuntimePermission
("getClassLoader")
permission to verify that retrieval of the context class loader is permitted.- Returns:
-
the context ClassLoader for this Thread, or
null
indicating the system class loader (or, failing that, the bootstrap class loader) - Throws:
-
SecurityException
- if the current thread cannot get the context ClassLoader - Since:
- 1.2
setContextClassLoader
public void setContextClassLoader(ClassLoader cl)
Sets the context ClassLoader for this Thread. The context ClassLoader can be set when a thread is created, and allows the creator of the thread to provide the appropriate class loader, throughgetContextClassLoader
, to code running in the thread when loading classes and resources.If a security manager is present, its
checkPermission
method is invoked with aRuntimePermission
("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:
-
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. 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 thegetStackTrace
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 deniesRuntimePermission
("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)
-
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