java.lang.Thread
|
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java.lang.Object
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:
exit method of class Runtime has been
called and the security manager has permitted the exit operation
to take place.
run method or by
throwing an exception that propagates beyond the run
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 the run method of class
Thread. 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 the run method. An instance of the class can
then be allocated, passed as an argument when creating
Thread, 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.
Runnable,
Runtime.exit(int),
run(),
stop()| Field Summary | |
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 | |
Thread()
Allocates a new Thread object. |
|
Thread(Runnable target)
Allocates a new Thread object. |
|
Thread(Runnable target,
String name)
Allocates a new Thread object. |
|
Thread(String name)
Allocates a new Thread object. |
|
Thread(ThreadGroup group,
Runnable target)
Allocates a new Thread object. |
|
Thread(ThreadGroup group,
Runnable target,
String name)
Allocates a new Thread object so that it has
target 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 target,
String name,
long stackSize)
Allocates a new Thread object so that it has
target as its run object, has the specified
name as its name, belongs to the thread group referred to
by group, and has the specified stack size. |
|
Thread(ThreadGroup group,
String name)
Allocates a new Thread object. |
|
| Method Summary | |
static int |
activeCount()
Returns the number of active threads in the current thread's thread group. |
void |
checkAccess()
Determines if the currently running thread has permission to modify this thread. |
int |
countStackFrames()
Deprecated. The definition of this call depends on suspend(),
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()
Destroys this thread, without any cleanup. |
static void |
dumpStack()
Prints a stack trace of the current thread. |
static int |
enumerate(Thread[] tarray)
Copies into the specified array every active thread in the current thread's thread group and its subgroups. |
ClassLoader |
getContextClassLoader()
Returns the context ClassLoader for this Thread. |
String |
getName()
Returns this thread's name. |
int |
getPriority()
Returns this thread's priority. |
ThreadGroup |
getThreadGroup()
Returns the thread group to which this thread belongs. |
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 most millis milliseconds for this thread to
die. |
void |
join(long millis,
int nanos)
Waits at most millis milliseconds plus
nanos nanoseconds for this thread to die. |
void |
resume()
Deprecated. 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?. |
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 |
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. |
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. |
static void |
sleep(long millis)
Causes the currently executing thread to sleep (temporarily cease execution) for the specified number of milliseconds. |
static void |
sleep(long millis,
int nanos)
Causes the currently executing thread to sleep (cease execution) for the specified number of milliseconds plus the specified number of nanoseconds. |
void |
start()
Causes this thread to begin execution; the Java Virtual Machine calls the run 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 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?. |
void |
stop(Throwable obj)
Deprecated. This method is inherently unsafe. See stop()
(with no arguments) for details. An additional danger of this
method is that it may be used to generate exceptions that the
target thread is unprepared to handle (including checked
exceptions that the thread could not possibly throw, were it
not for this method).
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 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?. |
String |
toString()
Returns a string representation of this thread, including the thread's name, priority, and thread group. |
static void |
yield()
Causes the currently executing thread object to temporarily pause and allow other threads to execute. |
| Methods inherited from class java.lang.Object |
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait |
| Field Detail |
public static final int MIN_PRIORITY
public static final int NORM_PRIORITY
public static final int MAX_PRIORITY
| Constructor Detail |
public Thread()
Thread object. 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.
Thread(java.lang.ThreadGroup,
java.lang.Runnable, java.lang.String)public Thread(Runnable target)
Thread object. This constructor has
the same effect as Thread(null, target,
gname), where gname is
a newly generated name. Automatically generated names are of the
form "Thread-"+n, where n is an integer.
target - the object whose run method is called.Thread(java.lang.ThreadGroup,
java.lang.Runnable, java.lang.String)
public Thread(ThreadGroup group,
Runnable target)
Thread object. This constructor has
the same effect as Thread(group, target,
gname), where gname is
a newly generated name. Automatically generated names are of the
form "Thread-"+n, where n is an integer.
group - the thread group.target - the object whose run method is called.
SecurityException - if the current thread cannot create a
thread in the specified thread group.Thread(java.lang.ThreadGroup,
java.lang.Runnable, java.lang.String)public Thread(String name)
Thread object. This constructor has
the same effect as Thread(null, null, name).
name - the name of the new thread.Thread(java.lang.ThreadGroup,
java.lang.Runnable, java.lang.String)
public Thread(ThreadGroup group,
String name)
Thread object. This constructor has
the same effect as Thread(group, null, name)
group - the thread group.name - the name of the new thread.
SecurityException - if the current thread cannot create a
thread in the specified thread group.Thread(java.lang.ThreadGroup,
java.lang.Runnable, java.lang.String)
public Thread(Runnable target,
String name)
Thread object. This constructor has
the same effect as Thread(null, target, name).
target - the object whose run method is called.name - the name of the new thread.Thread(java.lang.ThreadGroup,
java.lang.Runnable, java.lang.String)
public Thread(ThreadGroup group,
Runnable target,
String name)
Thread object so that it has
target as its run object, has the specified
name as its name, and belongs to the thread group
referred to by group.
If group is null and there is a
security manager, the group is determined by the security manager's
getThreadGroup method. If group is
null and there is not a security manager, or the
security manager's getThreadGroup method returns
null, the group is set to be the same ThreadGroup
as the thread that is creating the new thread.
If there is a security manager, its checkAccess
method is called with the ThreadGroup as its argument.
This may result in a SecurityException.
If the target argument is not null, the
run method of the target is called when
this thread is started. If the target argument is
null, this thread's run method is called
when this thread is started.
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.
group - the thread group.target - the object whose run method is called.name - the name of the new thread.
SecurityException - if the current thread cannot create a
thread in the specified thread group.Runnable.run(),
run(),
setDaemon(boolean),
setPriority(int),
ThreadGroup.checkAccess(),
SecurityManager.checkAccess(java.lang.Thread)
public Thread(ThreadGroup group,
Runnable target,
String name,
long stackSize)
Thread object so that it has
target as its run object, has the specified
name as its name, 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 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.
group - the thread group.target - the object whose run method is called.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.
SecurityException - if the current thread cannot create a
thread in the specified thread group.| Method Detail |
public static Thread currentThread()
public static void yield()
public static void sleep(long millis)
throws InterruptedException
millis - the length of time to sleep in milliseconds.
InterruptedException - if another thread has interrupted
the current thread. The interrupted status of the
current thread is cleared when this exception is thrown.Object.notify()
public static void sleep(long millis,
int nanos)
throws InterruptedException
millis - the length of time to sleep in milliseconds.nanos - 0-999999 additional nanoseconds to sleep.
IllegalArgumentException - if the value of millis is
negative or the value of nanos is not in the range
0-999999.
InterruptedException - if another thread has interrupted
the current thread. The interrupted status of the
current thread is cleared when this exception is thrown.Object.notify()public void start()
run 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 its
run method).
IllegalThreadStateException - if the thread was already
started.run(),
stop()public void run()
Runnable run object, then that
Runnable object's run method is called;
otherwise, this method does nothing and returns.
Subclasses of Thread should override this method.
run in interface Runnablestart(),
stop(),
Thread(java.lang.ThreadGroup,
java.lang.Runnable, java.lang.String),
Runnable.run()public final void stop()
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?.
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 dies). If a catch clause catches a
ThreadDeath 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.
SecurityException - if the current thread cannot
modify this thread.interrupt(),
checkAccess(),
run(),
start(),
ThreadDeath,
ThreadGroup.uncaughtException(java.lang.Thread,
java.lang.Throwable),
SecurityManager.checkAccess(Thread),
SecurityManager.checkPermission(java.security.Permission)public final void stop(Throwable obj)
stop()
(with no arguments) for details. An additional danger of this
method is that it may be used to generate exceptions that the
target thread is unprepared to handle (including checked
exceptions that the thread could not possibly throw, were it
not for this method).
For more information, see
Why
are Thread.stop, Thread.suspend and Thread.resume Deprecated?.
If there is a security manager installed, the checkAccess
method of this thread is called, which 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) or
obj is not an instance of ThreadDeath, the
security manager's checkPermission method (with the
RuntimePermission("stopThread") argument) is called in
addition.
Again, this may result in throwing a
SecurityException (in the current thread).
If the argument obj is null, a
NullPointerException is thrown (in the current thread).
The thread represented by this thread is forced to complete
whatever it is doing abnormally and to throw the
Throwable object obj as an exception. This
is an unusual action to take; normally, the stop method
that takes no arguments should be used.
It is permitted to stop a thread that has not yet been started. If the thread is eventually started, it immediately terminates.
obj - the Throwable object to be thrown.
SecurityException - if the current thread cannot modify
this thread.interrupt(),
checkAccess(),
run(),
start(),
stop(),
SecurityManager.checkAccess(Thread),
SecurityManager.checkPermission(java.security.Permission)public void interrupt()
First 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 interruptible
channel 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.
SecurityException - if the current thread cannot modify this threadpublic static boolean interrupted()
true if the current thread has been interrupted;
false otherwise.isInterrupted()public boolean isInterrupted()
true if this thread has been interrupted;
false otherwise.interrupted()public void destroy()
public final boolean isAlive()
true if this thread is alive;
false otherwise.public final void suspend()
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?.
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.
SecurityException - if the current thread cannot modify
this thread.checkAccess()public final void resume()
suspend(),
which has been deprecated because it is deadlock-prone.
For more information, see
Why
are Thread.stop, Thread.suspend and Thread.resume Deprecated?.
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.
SecurityException - if the current thread cannot modify this
thread.checkAccess(),
suspend()public final void setPriority(int newPriority)
First the checkAccess method of this thread is called
with no arguments. This may result in throwing a
SecurityException.
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.
newPriority - priority to set this thread to
IllegalArgumentException - If the priority is not in the
range MIN_PRIORITY to
MAX_PRIORITY.
SecurityException - if the current thread cannot modify
this thread.getPriority(),
checkAccess(),
getPriority(),
getThreadGroup(),
MAX_PRIORITY,
MIN_PRIORITY,
ThreadGroup.getMaxPriority()public final int getPriority()
setPriority(int),
setPriority(int)public final void setName(String name)
name.
First the checkAccess method of this thread is called
with no arguments. This may result in throwing a
SecurityException.
name - the new name for this thread.
SecurityException - if the current thread cannot modify this
thread.getName(),
checkAccess(),
getName()public final String getName()
setName(java.lang.String),
setName(java.lang.String)public final ThreadGroup getThreadGroup()
public static int activeCount()
public static int enumerate(Thread[] tarray)
enumerate method of the current thread's thread
group with the array argument.
First, if there is a security manager, that enumerate
method calls the security
manager's checkAccess method
with the thread group as its argument. This may result
in throwing a SecurityException.
tarray - an array of Thread objects to copy to
SecurityException - if a security manager exists and its
checkAccess method doesn't allow the operation.ThreadGroup.enumerate(java.lang.Thread[]),
SecurityManager.checkAccess(java.lang.ThreadGroup)public int countStackFrames()
suspend(),
which is deprecated. Further, the results of this call
were never well-defined.
IllegalThreadStateException - if this thread is not
suspended.
public final void join(long millis)
throws InterruptedException
millis milliseconds for this thread to
die. A timeout of 0 means to wait forever.
millis - the time to wait in milliseconds.
InterruptedException - if another thread has interrupted
the current thread. The interrupted status of the
current thread is cleared when this exception is thrown.
public final void join(long millis,
int nanos)
throws InterruptedException
millis milliseconds plus
nanos nanoseconds for this thread to die.
millis - the time to wait in milliseconds.nanos - 0-999999 additional nanoseconds to wait.
IllegalArgumentException - if the value of millis is negative
the value of nanos is not in the range 0-999999.
InterruptedException - if another thread has interrupted
the current thread. The interrupted status of the
current thread is cleared when this exception is thrown.
public final void join()
throws InterruptedException
InterruptedException - if another thread has interrupted
the current thread. The interrupted status of the
current thread is cleared when this exception is thrown.public static void dumpStack()
Throwable.printStackTrace()public final void setDaemon(boolean on)
This method must be called before the thread is started.
This method first calls the checkAccess method
of this thread
with no arguments. This may result in throwing a
SecurityException (in the current thread).
on - if true, marks this thread as a
daemon thread.
IllegalThreadStateException - if this thread is active.
SecurityException - if the current thread cannot modify
this thread.isDaemon(),
checkAccess()public final boolean isDaemon()
true if this thread is a daemon thread;
false otherwise.setDaemon(boolean)public final void checkAccess()
If there is a security manager, its checkAccess method
is called with this thread as its argument. This may result in
throwing a SecurityException.
Note: This method was mistakenly non-final in JDK 1.1. It has been made final in the Java 2 Platform.
SecurityException - if the current thread is not allowed to
access this thread.SecurityManager.checkAccess(java.lang.Thread)public String toString()
toString in class Objectpublic ClassLoader getContextClassLoader()
First, if there is a security manager, and the caller's class
loader is not null and the caller's class loader is not the same as or
an ancestor of the context class loader for the thread whose
context class loader is being requested, then the security manager's
checkPermission
method is called with a
RuntimePermission("getClassLoader") permission
to see if it's ok to get the context ClassLoader..
SecurityException - if a security manager exists and its
checkPermission method doesn't allow
getting the context ClassLoader.setContextClassLoader(java.lang.ClassLoader),
SecurityManager.checkPermission(java.security.Permission),
RuntimePermissionpublic void setContextClassLoader(ClassLoader cl)
First, if there is a security manager, its checkPermission
method is called with a
RuntimePermission("setContextClassLoader") permission
to see if it's ok to set the context ClassLoader..
cl - the context ClassLoader for this Thread
SecurityException - if the current thread cannot set the
context ClassLoader.getContextClassLoader(),
SecurityManager.checkPermission(java.security.Permission),
RuntimePermissionpublic static boolean holdsLock(Object obj)
This method is designed to allow a program to assert that the current thread already holds a specified lock:
assert Thread.holdsLock(obj);
obj - the object on which to test lock ownership
NullPointerException - if obj is null
|
JavaTM 2 Platform Std. Ed. v1.4.2 |
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Copyright 2003 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.