ICondition Interface
Definition
Important
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Condition factors out the Object monitor
methods (Object#wait() wait, Object#notify notify
and Object#notifyAll notifyAll) into distinct objects to
give the effect of having multiple wait-sets per object, by
combining them with the use of arbitrary Lock implementations.
[Android.Runtime.Register("java/util/concurrent/locks/Condition", "", "Java.Util.Concurrent.Locks.IConditionInvoker")]
public interface ICondition : Android.Runtime.IJavaObject, IDisposable, Java.Interop.IJavaPeerable[<Android.Runtime.Register("java/util/concurrent/locks/Condition", "", "Java.Util.Concurrent.Locks.IConditionInvoker")>]
type ICondition = interface
interface IJavaObject
interface IDisposable
interface IJavaPeerable- Derived
- Attributes
- Implements
Remarks
Condition factors out the Object monitor methods (Object#wait() wait, Object#notify notify and Object#notifyAll notifyAll) into distinct objects to give the effect of having multiple wait-sets per object, by combining them with the use of arbitrary Lock implementations. Where a Lock replaces the use of synchronized methods and statements, a Condition replaces the use of the Object monitor methods.
Conditions (also known as <em>condition queues</em> or <em>condition variables</em>) provide a means for one thread to suspend execution (to "wait") until notified by another thread that some state condition may now be true. Because access to this shared state information occurs in different threads, it must be protected, so a lock of some form is associated with the condition. The key property that waiting for a condition provides is that it <em>atomically</em> releases the associated lock and suspends the current thread, just like Object.wait.
A Condition instance is intrinsically bound to a lock. To obtain a Condition instance for a particular Lock instance use its Lock#newCondition newCondition() method.
As an example, suppose we have a bounded buffer which supports put and take methods. If a take is attempted on an empty buffer, then the thread will block until an item becomes available; if a put is attempted on a full buffer, then the thread will block until a space becomes available. We would like to keep waiting put threads and take threads in separate wait-sets so that we can use the optimization of only notifying a single thread at a time when items or spaces become available in the buffer. This can be achieved using two Condition instances.
class BoundedBuffer<E> {
<b>final Lock lock = new ReentrantLock();</b>
final Condition notFull = <b>lock.newCondition(); </b>
final Condition notEmpty = <b>lock.newCondition(); </b>
final Object[] items = new Object[100];
int putptr, takeptr, count;
public void put(E x) throws InterruptedException {
<b>lock.lock();
try {</b>
while (count == items.length)
<b>notFull.await();</b>
items[putptr] = x;
if (++putptr == items.length) putptr = 0;
++count;
<b>notEmpty.signal();</b>
<b>} finally {
lock.unlock();
}</b>
}
public E take() throws InterruptedException {
<b>lock.lock();
try {</b>
while (count == 0)
<b>notEmpty.await();</b>
E x = (E) items[takeptr];
if (++takeptr == items.length) takeptr = 0;
--count;
<b>notFull.signal();</b>
return x;
<b>} finally {
lock.unlock();
}</b>
}
}
(The java.util.concurrent.ArrayBlockingQueue class provides this functionality, so there is no reason to implement this sample usage class.)
A Condition implementation can provide behavior and semantics that is different from that of the Object monitor methods, such as guaranteed ordering for notifications, or not requiring a lock to be held when performing notifications. If an implementation provides such specialized semantics then the implementation must document those semantics.
Note that Condition instances are just normal objects and can themselves be used as the target in a synchronized statement, and can have their own monitor Object#wait wait and Object#notify notify methods invoked. Acquiring the monitor lock of a Condition instance, or using its monitor methods, has no specified relationship with acquiring the Lock associated with that Condition or the use of its #await waiting and #signal signalling methods. It is recommended that to avoid confusion you never use Condition instances in this way, except perhaps within their own implementation.
Except where noted, passing a null value for any parameter will result in a NullPointerException being thrown.
<h2>Implementation Considerations</h2>
When waiting upon a Condition, a "<em>spurious wakeup</em>" is permitted to occur, in general, as a concession to the underlying platform semantics. This has little practical impact on most application programs as a Condition should always be waited upon in a loop, testing the state predicate that is being waited for. An implementation is free to remove the possibility of spurious wakeups but it is recommended that applications programmers always assume that they can occur and so always wait in a loop.
The three forms of condition waiting (interruptible, non-interruptible, and timed) may differ in their ease of implementation on some platforms and in their performance characteristics. In particular, it may be difficult to provide these features and maintain specific semantics such as ordering guarantees. Further, the ability to interrupt the actual suspension of the thread may not always be feasible to implement on all platforms.
Consequently, an implementation is not required to define exactly the same guarantees or semantics for all three forms of waiting, nor is it required to support interruption of the actual suspension of the thread.
An implementation is required to clearly document the semantics and guarantees provided by each of the waiting methods, and when an implementation does support interruption of thread suspension then it must obey the interruption semantics as defined in this interface.
As interruption generally implies cancellation, and checks for interruption are often infrequent, an implementation can favor responding to an interrupt over normal method return. This is true even if it can be shown that the interrupt occurred after another action that may have unblocked the thread. An implementation should document this behavior.
Added in 1.5.
Java documentation for java.util.concurrent.locks.Condition.
Portions of this page are modifications based on work created and shared by the Android Open Source Project and used according to terms described in the Creative Commons 2.5 Attribution License.
Properties
| Handle |
Gets the JNI value of the underlying Android object. (Inherited from IJavaObject) |
| JniIdentityHashCode |
Returns the value of |
| JniManagedPeerState |
State of the managed peer. (Inherited from IJavaPeerable) |
| JniPeerMembers |
Member access and invocation support. (Inherited from IJavaPeerable) |
| PeerReference |
Returns a JniObjectReference of the wrapped Java object instance. (Inherited from IJavaPeerable) |
Methods
| Await() |
Causes the current thread to wait until it is signalled or Thread#interrupt interrupted. |
| Await(Int64, TimeUnit) |
Causes the current thread to wait until it is signalled or interrupted, or the specified waiting time elapses. |
| AwaitNanos(Int64) |
Causes the current thread to wait until it is signalled or interrupted, or the specified waiting time elapses. |
| AwaitUninterruptibly() |
Causes the current thread to wait until it is signalled. |
| AwaitUntil(Date) |
Causes the current thread to wait until it is signalled or interrupted, or the specified deadline elapses. |
| Disposed() |
Called when the instance has been disposed. (Inherited from IJavaPeerable) |
| DisposeUnlessReferenced() |
If there are no outstanding references to this instance, then
calls |
| Finalized() |
Called when the instance has been finalized. (Inherited from IJavaPeerable) |
| SetJniIdentityHashCode(Int32) |
Set the value returned by |
| SetJniManagedPeerState(JniManagedPeerStates) | (Inherited from IJavaPeerable) |
| SetPeerReference(JniObjectReference) |
Set the value returned by |
| Signal() |
Wakes up one waiting thread. |
| SignalAll() |
Wakes up all waiting threads. |
| UnregisterFromRuntime() |
Unregister this instance so that the runtime will not return it from future Java.Interop.JniRuntime+JniValueManager.PeekValue invocations. (Inherited from IJavaPeerable) |
Extension Methods
| JavaCast<TResult>(IJavaObject) |
Performs an Android runtime-checked type conversion. |
| JavaCast<TResult>(IJavaObject) | |
| GetJniTypeName(IJavaPeerable) | |