JavaTM 2 Platform Std. Ed. v1.5.0
java.util.concurrent.locks
Class AbstractQueuedSynchronizer
java.lang.Object
java.util.concurrent.locks.AbstractQueuedSynchronizer
- All Implemented Interfaces:
- Serializable
public abstract class AbstractQueuedSynchronizer - extends Object
- implements Serializable
Provides a framework for implementing blocking locks and related
synchronizers (semaphores, events, etc) that rely on
first-in-first-out (FIFO) wait queues. This class is designed to
be a useful basis for most kinds of synchronizers that rely on a
single atomic int value to represent state. Subclasses
must define the protected methods that change this state, and which
define what that state means in terms of this object being acquired
or released. Given these, the other methods in this class carry
out all queuing and blocking mechanics. Subclasses can maintain
other state fields, but only the atomically updated int
value manipulated using methods getState() , setState(int) and compareAndSetState(int, int) is tracked with respect
to synchronization.
Subclasses should be defined as non-public internal helper
classes that are used to implement the synchronization properties
of their enclosing class. Class
AbstractQueuedSynchronizer does not implement any
synchronization interface. Instead it defines methods such as
acquireInterruptibly(int) that can be invoked as
appropriate by concrete locks and related synchronizers to
implement their public methods.
This class supports either or both a default exclusive
mode and a shared mode. When acquired in exclusive mode,
attempted acquires by other threads cannot succeed. Shared mode
acquires by multiple threads may (but need not) succeed. This class
does not "understand" these differences except in the
mechanical sense that when a shared mode acquire succeeds, the next
waiting thread (if one exists) must also determine whether it can
acquire as well. Threads waiting in the different modes share the
same FIFO queue. Usually, implementation subclasses support only
one of these modes, but both can come into play for example in a
ReadWriteLock . Subclasses that support only exclusive or
only shared modes need not define the methods supporting the unused mode.
This class defines a nested AbstractQueuedSynchronizer.ConditionObject class that
can be used as a Condition implementation by subclasses
supporting exclusive mode for which method isHeldExclusively() reports whether synchronization is exclusively
held with respect to the current thread, method release(int)
invoked with the current getState() value fully releases
this object, and acquire(int) , given this saved state value,
eventually restores this object to its previous acquired state. No
AbstractQueuedSynchronizer method otherwise creates such a
condition, so if this constraint cannot be met, do not use it. The
behavior of AbstractQueuedSynchronizer.ConditionObject depends of course on the
semantics of its synchronizer implementation.
This class provides inspection, instrumentation, and monitoring
methods for the internal queue, as well as similar methods for
condition objects. These can be exported as desired into classes
using an AbstractQueuedSynchronizer for their
synchronization mechanics.
Serialization of this class stores only the underlying atomic
integer maintaining state, so deserialized objects have empty
thread queues. Typical subclasses requiring serializability will
define a readObject method that restores this to a known
initial state upon deserialization.
Usage
To use this class as the basis of a synchronizer, redefine the
following methods, as applicable, by inspecting and/or modifying
the synchronization state using getState() , setState(int) and/or compareAndSetState(int, int) :
Each of these methods by default throws UnsupportedOperationException . Implementations of these methods
must be internally thread-safe, and should in general be short and
not block. Defining these methods is the only supported
means of using this class. All other methods are declared
final because they cannot be independently varied.
Even though this class is based on an internal FIFO queue, it
does not automatically enforce FIFO acquisition policies. The core
of exclusive synchronization takes the form:
Acquire:
while (!tryAcquire(arg)) {
enqueue thread if it is not already queued;
possibly block current thread;
}
Release:
if (tryRelease(arg))
unblock the first queued thread;
(Shared mode is similar but may involve cascading signals.)
Because checks in acquire are invoked before enqueuing, a newly
acquiring thread may barge ahead of others that are
blocked and queued. However, you can, if desired, define
tryAcquire and/or tryAcquireShared to disable
barging by internally invoking one or more of the inspection
methods. In particular, a strict FIFO lock can define
tryAcquire to immediately return false if getFirstQueuedThread() does not return the current thread. A
normally preferable non-strict fair version can immediately return
false only if hasQueuedThreads() returns
true and getFirstQueuedThread is not the current
thread; or equivalently, that getFirstQueuedThread is both
non-null and not the current thread. Further variations are
possible.
Throughput and scalability are generally highest for the
default barging (also known as greedy,
renouncement, and convoy-avoidance) strategy.
While this is not guaranteed to be fair or starvation-free, earlier
queued threads are allowed to recontend before later queued
threads, and each recontention has an unbiased chance to succeed
against incoming threads. Also, while acquires do not
"spin" in the usual sense, they may perform multiple
invocations of tryAcquire interspersed with other
computations before blocking. This gives most of the benefits of
spins when exclusive synchronization is only briefly held, without
most of the liabilities when it isn't. If so desired, you can
augment this by preceding calls to acquire methods with
"fast-path" checks, possibly prechecking hasContended()
and/or hasQueuedThreads() to only do so if the synchronizer
is likely not to be contended.
This class provides an efficient and scalable basis for
synchronization in part by specializing its range of use to
synchronizers that can rely on int state, acquire, and
release parameters, and an internal FIFO wait queue. When this does
not suffice, you can build synchronizers from a lower level using
atomic classes, your own custom
Queue classes, and LockSupport blocking
support.
Usage Examples
Here is a non-reentrant mutual exclusion lock class that uses
the value zero to represent the unlocked state, and one to
represent the locked state. It also supports conditions and exposes
one of the instrumentation methods:
class Mutex implements Lock, java.io.Serializable {
// Our internal helper class
private static class Sync extends AbstractQueuedSynchronizer {
// Report whether in locked state
protected boolean isHeldExclusively() {
return getState() == 1;
}
// Acquire the lock if state is zero
public boolean tryAcquire(int acquires) {
assert acquires == 1; // Otherwise unused
return compareAndSetState(0, 1);
}
// Release the lock by setting state to zero
protected boolean tryRelease(int releases) {
assert releases == 1; // Otherwise unused
if (getState() == 0) throw new IllegalMonitorStateException();
setState(0);
return true;
}
// Provide a Condition
Condition newCondition() { return new ConditionObject(); }
// Deserialize properly
private void readObject(ObjectInputStream s) throws IOException, ClassNotFoundException {
s.defaultReadObject();
setState(0); // reset to unlocked state
}
}
// The sync object does all the hard work. We just forward to it.
private final Sync sync = new Sync();
public void lock() { sync.acquire(1); }
public boolean tryLock() { return sync.tryAcquire(1); }
public void unlock() { sync.release(1); }
public Condition newCondition() { return sync.newCondition(); }
public boolean isLocked() { return sync.isHeldExclusively(); }
public boolean hasQueuedThreads() { return sync.hasQueuedThreads(); }
public void lockInterruptibly() throws InterruptedException {
sync.acquireInterruptibly(1);
}
public boolean tryLock(long timeout, TimeUnit unit) throws InterruptedException {
return sync.tryAcquireNanos(1, unit.toNanos(timeout));
}
}
Here is a latch class that is like a CountDownLatch
except that it only requires a single signal to
fire. Because a latch is non-exclusive, it uses the shared
acquire and release methods.
class BooleanLatch {
private static class Sync extends AbstractQueuedSynchronizer {
boolean isSignalled() { return getState() != 0; }
protected int tryAcquireShared(int ignore) {
return isSignalled()? 1 : -1;
}
protected boolean tryReleaseShared(int ignore) {
setState(1);
return true;
}
}
private final Sync sync = new Sync();
public boolean isSignalled() { return sync.isSignalled(); }
public void signal() { sync.releaseShared(1); }
public void await() throws InterruptedException {
sync.acquireSharedInterruptibly(1);
}
}
- Since:
- 1.5
- See Also:
- Serialized Form
Constructor Summary |
protected |
AbstractQueuedSynchronizer()
Creates a new AbstractQueuedSynchronizer instance
with initial synchronization state of zero. |
Method Summary |
void |
acquire(int arg)
Acquires in exclusive mode, ignoring interrupts. |
void |
acquireInterruptibly(int arg)
Acquires in exclusive mode, aborting if interrupted. |
void |
acquireShared(int arg)
Acquires in shared mode, ignoring interrupts. |
void |
acquireSharedInterruptibly(int arg)
Acquires in shared mode, aborting if interrupted. |
protected boolean |
compareAndSetState(int expect,
int update)
Atomically sets synchronization state to the given updated
value if the current state value equals the expected value. |
Collection<Thread> |
getExclusiveQueuedThreads()
Returns a collection containing threads that may be waiting to
acquire in exclusive mode. |
Thread |
getFirstQueuedThread()
Returns the first (longest-waiting) thread in the queue, or
null if no threads are currently queued. |
Collection<Thread> |
getQueuedThreads()
Returns a collection containing threads that may be waiting to
acquire. |
int |
getQueueLength()
Returns an estimate of the number of threads waiting to
acquire. |
Collection<Thread> |
getSharedQueuedThreads()
Returns a collection containing threads that may be waiting to
acquire in shared mode. |
protected int |
getState()
Returns the current value of synchronization state. |
Collection<Thread> |
getWaitingThreads(AbstractQueuedSynchronizer.ConditionObject condition)
Returns a collection containing those threads that may be
waiting on the given condition associated with this
synchronizer. |
int |
getWaitQueueLength(AbstractQueuedSynchronizer.ConditionObject condition)
Returns an estimate of the number of threads waiting on the
given condition associated with this synchronizer. |
boolean |
hasContended()
Queries whether any threads have ever contended to acquire this
synchronizer; that is if an acquire method has ever blocked. |
boolean |
hasQueuedThreads()
Queries whether any threads are waiting to acquire. |
boolean |
hasWaiters(AbstractQueuedSynchronizer.ConditionObject condition)
Queries whether any threads are waiting on the given condition
associated with this synchronizer. |
protected boolean |
isHeldExclusively()
Returns true if synchronization is held exclusively with respect
to the current (calling) thread. |
boolean |
isQueued(Thread thread)
Returns true if the given thread is currently queued. |
boolean |
owns(AbstractQueuedSynchronizer.ConditionObject condition)
Queries whether the given ConditionObject
uses this synchronizer as its lock. |
boolean |
release(int arg)
Releases in exclusive mode. |
boolean |
releaseShared(int arg)
Releases in shared mode. |
protected void |
setState(int newState)
Sets the value of synchronization state. |
String |
toString()
Returns a string identifying this synchronizer, as well as its
state. |
protected boolean |
tryAcquire(int arg)
Attempts to acquire in exclusive mode. |
boolean |
tryAcquireNanos(int arg,
long nanosTimeout)
Attempts to acquire in exclusive mode, aborting if interrupted,
and failing if the given timeout elapses. |
protected int |
tryAcquireShared(int arg)
Attempts to acquire in shared mode. |
boolean |
tryAcquireSharedNanos(int arg,
long nanosTimeout)
Attempts to acquire in shared mode, aborting if interrupted, and
failing if the given timeout elapses. |
protected boolean |
tryRelease(int arg)
Attempts to set the state to reflect a release in exclusive
mode. |
protected boolean |
tryReleaseShared(int arg)
Attempts to set the state to reflect a release in shared mode. |
AbstractQueuedSynchronizer
protected AbstractQueuedSynchronizer()
- Creates a new AbstractQueuedSynchronizer instance
with initial synchronization state of zero.
getState
protected final int getState()
- Returns the current value of synchronization state.
This operation has memory semantics of a volatile read.
- Returns:
- current state value
setState
protected final void setState(int newState)
- Sets the value of synchronization state.
This operation has memory semantics of a volatile write.
- Parameters:
newState - the new state value
compareAndSetState
protected final boolean compareAndSetState(int expect,
int update)
- Atomically sets synchronization state to the given updated
value if the current state value equals the expected value.
This operation has memory semantics of a volatile read
and write.
- Parameters:
expect - the expected valueupdate - the new value
- Returns:
- true if successful. False return indicates that
the actual value was not equal to the expected value.
tryAcquire
protected boolean tryAcquire(int arg)
- Attempts to acquire in exclusive mode. This method should query
if the state of the object permits it to be acquired in the
exclusive mode, and if so to acquire it.
This method is always invoked by the thread performing
acquire. If this method reports failure, the acquire method
may queue the thread, if it is not already queued, until it is
signalled by a release from some other thread. This can be used
to implement method Lock.tryLock() .
The default
implementation throws UnsupportedOperationException
- Parameters:
arg - the acquire argument. This value
is always the one passed to an acquire method,
or is the value saved on entry to a condition wait.
The value is otherwise uninterpreted and can represent anything
you like.
- Returns:
- true if successful. Upon success, this object has been
acquired.
- Throws:
IllegalMonitorStateException - if acquiring would place
this synchronizer in an illegal state. This exception must be
thrown in a consistent fashion for synchronization to work
correctly.
UnsupportedOperationException - if exclusive mode is not supported
tryRelease
protected boolean tryRelease(int arg)
- Attempts to set the state to reflect a release in exclusive
mode.
This method is always invoked by the thread
performing release.
The default implementation throws
UnsupportedOperationException
- Parameters:
arg - the release argument. This value
is always the one passed to a release method,
or the current state value upon entry to a condition wait.
The value is otherwise uninterpreted and can represent anything
you like.
- Returns:
- true if this object is now in a fully released state,
so that any waiting threads may attempt to acquire; and false
otherwise.
- Throws:
IllegalMonitorStateException - if releasing would place
this synchronizer in an illegal state. This exception must be
thrown in a consistent fashion for synchronization to work
correctly.
UnsupportedOperationException - if exclusive mode is not supported
tryAcquireShared
protected int tryAcquireShared(int arg)
- Attempts to acquire in shared mode. This method should query if
the state of the object permits it to be acquired in the shared
mode, and if so to acquire it.
This method is always invoked by the thread performing
acquire. If this method reports failure, the acquire method
may queue the thread, if it is not already queued, until it is
signalled by a release from some other thread.
The default implementation throws UnsupportedOperationException
- Parameters:
arg - the acquire argument. This value
is always the one passed to an acquire method,
or is the value saved on entry to a condition wait.
The value is otherwise uninterpreted and can represent anything
you like.
- Returns:
- a negative value on failure, zero on exclusive success,
and a positive value if non-exclusively successful, in which
case a subsequent waiting thread must check
availability. (Support for three different return values
enables this method to be used in contexts where acquires only
sometimes act exclusively.) Upon success, this object has been
acquired.
- Throws:
IllegalMonitorStateException - if acquiring would place
this synchronizer in an illegal state. This exception must be
thrown in a consistent fashion for synchronization to work
correctly.
UnsupportedOperationException - if shared mode is not supported
tryReleaseShared
protected boolean tryReleaseShared(int arg)
- Attempts to set the state to reflect a release in shared mode.
This method is always invoked by the thread performing release.
The default implementation throws
UnsupportedOperationException
- Parameters:
arg - the release argument. This value
is always the one passed to a release method,
or the current state value upon entry to a condition wait.
The value is otherwise uninterpreted and can represent anything
you like.
- Returns:
- true if this object is now in a fully released state,
so that any waiting threads may attempt to acquire; and false
otherwise.
- Throws:
IllegalMonitorStateException - if releasing would place
this synchronizer in an illegal state. This exception must be
thrown in a consistent fashion for synchronization to work
correctly.
UnsupportedOperationException - if shared mode is not supported
isHeldExclusively
protected boolean isHeldExclusively()
- Returns true if synchronization is held exclusively with respect
to the current (calling) thread. This method is invoked
upon each call to a non-waiting
AbstractQueuedSynchronizer.ConditionObject method.
(Waiting methods instead invoke release(int) .)
The default implementation throws UnsupportedOperationException . This method is invoked
internally only within AbstractQueuedSynchronizer.ConditionObject methods, so need
not be defined if conditions are not used.
- Returns:
- true if synchronization is held exclusively;
else false
- Throws:
UnsupportedOperationException - if conditions are not supported
acquire
public final void acquire(int arg)
- Acquires in exclusive mode, ignoring interrupts. Implemented
by invoking at least once
tryAcquire(int) ,
returning on success. Otherwise the thread is queued, possibly
repeatedly blocking and unblocking, invoking tryAcquire(int) until success. This method can be used
to implement method Lock.lock()
- Parameters:
arg - the acquire argument.
This value is conveyed to tryAcquire(int) but is
otherwise uninterpreted and can represent anything
you like.
acquireInterruptibly
public final void acquireInterruptibly(int arg)
throws InterruptedException
- Acquires in exclusive mode, aborting if interrupted.
Implemented by first checking interrupt status, then invoking
at least once
tryAcquire(int) , returning on
success. Otherwise the thread is queued, possibly repeatedly
blocking and unblocking, invoking tryAcquire(int)
until success or the thread is interrupted. This method can be
used to implement method Lock.lockInterruptibly()
- Parameters:
arg - the acquire argument.
This value is conveyed to tryAcquire(int) but is
otherwise uninterpreted and can represent anything
you like.
- Throws:
InterruptedException - if the current thread is interrupted
tryAcquireNanos
public final boolean tryAcquireNanos(int arg,
long nanosTimeout)
throws InterruptedException
- Attempts to acquire in exclusive mode, aborting if interrupted,
and failing if the given timeout elapses. Implemented by first
checking interrupt status, then invoking at least once
tryAcquire(int) , returning on success. Otherwise, the thread is
queued, possibly repeatedly blocking and unblocking, invoking
tryAcquire(int) until success or the thread is interrupted
or the timeout elapses. This method can be used to implement
method Lock.tryLock(long, TimeUnit) .
- Parameters:
arg - the acquire argument.
This value is conveyed to tryAcquire(int) but is
otherwise uninterpreted and can represent anything
you like.nanosTimeout - the maximum number of nanoseconds to wait
- Returns:
- true if acquired; false if timed out
- Throws:
InterruptedException - if the current thread is interrupted
release
public final boolean release(int arg)
- Releases in exclusive mode. Implemented by unblocking one or
more threads if
tryRelease(int) returns true.
This method can be used to implement method Lock.unlock()
- Parameters:
arg - the release argument.
This value is conveyed to tryRelease(int) but is
otherwise uninterpreted and can represent anything
you like.
- Returns:
- the value returned from
tryRelease(int)
acquireShared
public final void acquireShared(int arg)
- Acquires in shared mode, ignoring interrupts. Implemented by
first invoking at least once
tryAcquireShared(int) ,
returning on success. Otherwise the thread is queued, possibly
repeatedly blocking and unblocking, invoking tryAcquireShared(int) until success.
- Parameters:
arg - the acquire argument.
This value is conveyed to tryAcquireShared(int) but is
otherwise uninterpreted and can represent anything
you like.
acquireSharedInterruptibly
public final void acquireSharedInterruptibly(int arg)
throws InterruptedException
- Acquires in shared mode, aborting if interrupted. Implemented
by first checking interrupt status, then invoking at least once
tryAcquireShared(int) , returning on success. Otherwise the
thread is queued, possibly repeatedly blocking and unblocking,
invoking tryAcquireShared(int) until success or the thread
is interrupted.
- Parameters:
arg - the acquire argument.
This value is conveyed to tryAcquireShared(int) but is
otherwise uninterpreted and can represent anything
you like.
- Throws:
InterruptedException - if the current thread is interrupted
tryAcquireSharedNanos
public final boolean tryAcquireSharedNanos(int arg,
long nanosTimeout)
throws InterruptedException
- Attempts to acquire in shared mode, aborting if interrupted, and
failing if the given timeout elapses. Implemented by first
checking interrupt status, then invoking at least once
tryAcquireShared(int) , returning on success. Otherwise, the
thread is queued, possibly repeatedly blocking and unblocking,
invoking tryAcquireShared(int) until success or the thread
is interrupted or the timeout elapses.
- Parameters:
arg - the acquire argument.
This value is conveyed to tryAcquireShared(int) but is
otherwise uninterpreted and can represent anything
you like.nanosTimeout - the maximum number of nanoseconds to wait
- Returns:
- true if acquired; false if timed out
- Throws:
InterruptedException - if the current thread is interrupted
releaseShared
public final boolean releaseShared(int arg)
- Releases in shared mode. Implemented by unblocking one or more
threads if
tryReleaseShared(int) returns true.
- Parameters:
arg - the release argument.
This value is conveyed to tryReleaseShared(int) but is
otherwise uninterpreted and can represent anything
you like.
- Returns:
- the value returned from
tryReleaseShared(int)
hasQueuedThreads
public final boolean hasQueuedThreads()
- Queries whether any threads are waiting to acquire. Note that
because cancellations due to interrupts and timeouts may occur
at any time, a true return does not guarantee that any
other thread will ever acquire.
In this implementation, this operation returns in
constant time.
- Returns:
- true if there may be other threads waiting to acquire
the lock.
hasContended
public final boolean hasContended()
- Queries whether any threads have ever contended to acquire this
synchronizer; that is if an acquire method has ever blocked.
In this implementation, this operation returns in
constant time.
- Returns:
- true if there has ever been contention
getFirstQueuedThread
public final Thread getFirstQueuedThread()
- Returns the first (longest-waiting) thread in the queue, or
null if no threads are currently queued.
In this implementation, this operation normally returns in
constant time, but may iterate upon contention if other threads are
concurrently modifying the queue.
- Returns:
- the first (longest-waiting) thread in the queue, or
null if no threads are currently queued.
isQueued
public final boolean isQueued(Thread thread)
- Returns true if the given thread is currently queued.
This implementation traverses the queue to determine
presence of the given thread.
- Parameters:
thread - the thread
- Returns:
- true if the given thread in on the queue
- Throws:
NullPointerException - if thread null
getQueueLength
public final int getQueueLength()
- Returns an estimate of the number of threads waiting to
acquire. The value is only an estimate because the number of
threads may change dynamically while this method traverses
internal data structures. This method is designed for use in
monitoring system state, not for synchronization
control.
- Returns:
- the estimated number of threads waiting for this lock
getQueuedThreads
public final Collection<Thread> getQueuedThreads()
- Returns a collection containing threads that may be waiting to
acquire. Because the actual set of threads may change
dynamically while constructing this result, the returned
collection is only a best-effort estimate. The elements of the
returned collection are in no particular order. This method is
designed to facilitate construction of subclasses that provide
more extensive monitoring facilities.
- Returns:
- the collection of threads
getExclusiveQueuedThreads
public final Collection<Thread> getExclusiveQueuedThreads()
- Returns a collection containing threads that may be waiting to
acquire in exclusive mode. This has the same properties
as
getQueuedThreads() except that it only returns
those threads waiting due to an exclusive acquire.
- Returns:
- the collection of threads
getSharedQueuedThreads
public final Collection<Thread> getSharedQueuedThreads()
- Returns a collection containing threads that may be waiting to
acquire in shared mode. This has the same properties
as
getQueuedThreads() except that it only returns
those threads waiting due to a shared acquire.
- Returns:
- the collection of threads
toString
public String toString()
- Returns a string identifying this synchronizer, as well as its
state. The state, in brackets, includes the String "State
=" followed by the current value of
getState() , and
either "nonempty" or "empty" depending on
whether the queue is empty.
- Overrides:
toString in class Object
- Returns:
- a string identifying this synchronizer, as well as its state.
owns
public final boolean owns(AbstractQueuedSynchronizer.ConditionObject condition)
- Queries whether the given ConditionObject
uses this synchronizer as its lock.
- Parameters:
condition - the condition
- Returns:
- true if owned
- Throws:
NullPointerException - if condition null
hasWaiters
public final boolean hasWaiters(AbstractQueuedSynchronizer.ConditionObject condition)
- Queries whether any threads are waiting on the given condition
associated with this synchronizer. Note that because timeouts
and interrupts may occur at any time, a true return
does not guarantee that a future signal will awaken
any threads. This method is designed primarily for use in
monitoring of the system state.
- Parameters:
condition - the condition
- Returns:
- true if there are any waiting threads.
- Throws:
IllegalMonitorStateException - if exclusive synchronization
is not held
IllegalArgumentException - if the given condition is
not associated with this synchronizer
NullPointerException - if condition null
getWaitQueueLength
public final int getWaitQueueLength(AbstractQueuedSynchronizer.ConditionObject condition)
- Returns an estimate of the number of threads waiting on the
given condition associated with this synchronizer. Note that
because timeouts and interrupts may occur at any time, the
estimate serves only as an upper bound on the actual number of
waiters. This method is designed for use in monitoring of the
system state, not for synchronization control.
- Parameters:
condition - the condition
- Returns:
- the estimated number of waiting threads.
- Throws:
IllegalMonitorStateException - if exclusive synchronization
is not held
IllegalArgumentException - if the given condition is
not associated with this synchronizer
NullPointerException - if condition null
getWaitingThreads
public final Collection<Thread> getWaitingThreads(AbstractQueuedSynchronizer.ConditionObject condition)
- Returns a collection containing those threads that may be
waiting on the given condition associated with this
synchronizer. Because the actual set of threads may change
dynamically while constructing this result, the returned
collection is only a best-effort estimate. The elements of the
returned collection are in no particular order.
- Parameters:
condition - the condition
- Returns:
- the collection of threads
- Throws:
IllegalMonitorStateException - if exclusive synchronization
is not held
IllegalArgumentException - if the given condition is
not associated with this synchronizer
NullPointerException - if condition null
Copyright 2003 Sun Microsystems, Inc. All rights reserved
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