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Class `core.sync.condition.Condition`

This class represents a condition variable as conceived by C.A.R. Hoare. As per Mesa type monitors however, "signal" has been replaced with "notify" to indicate that control is not transferred to the waiter when a notification is sent.


						
				class Condition
				;

Constructors

Name	Description
`this` (m)	Initializes a condition object which is associated with the supplied mutex object.

Properties

Name	Type	Description
`mutex`[get]	`Mutex`	Gets the mutex associated with this condition.

Methods

Name	Description
`notify` ()	Notifies one waiter.
`notifyAll` ()	Notifies all waiters.
`wait` ()	Wait until notified.
`wait` (val)	Suspends the calling thread until a notification occurs or until the supplied time period has elapsed.
`factory` (classname)	Create instance of class specified by the fully qualified name classname. The class must either have no constructors or have a default constructor.
`opCmp` (o)	Compare with another Object obj.
`opEquals` (o)	Test whether `this` is equal to `o`. The default implementation only compares by identity (using the `is` operator). Generally, overrides and overloads for `opEquals` should attempt to compare objects by their contents. A class will most likely want to add an overload that takes your specific type as the argument and does the content comparison. Then you can override this and forward it to your specific typed overload with a cast. Remember to check for `null` on the typed overload.
`toHash` ()	Compute hash function for Object.
`toString` ()	Convert Object to a human readable string.

Example

import core.thread;
import core.sync.mutex;
import core.sync.semaphore;


void testNotify()
{
    auto mutex      = new Mutex;
    auto condReady  = new Condition( mutex );
    auto semDone    = new Semaphore;
    auto synLoop    = new Object;
    int  numWaiters = 10;
    int  numTries   = 10;
    int  numReady   = 0;
    int  numTotal   = 0;
    int  numDone    = 0;
    int  numPost    = 0;

    void waiter()
    {
        for ( int i = 0; i < numTries; ++i )
        {
            synchronized( mutex )
            {
                while ( numReady < 1 )
                {
                    condReady.wait();
                }
                --numReady;
                ++numTotal;
            }

            synchronized( synLoop )
            {
                ++numDone;
            }
            semDone.wait();
        }
    }

    auto group = new ThreadGroup;

    for ( int i = 0; i < numWaiters; ++i )
        group.create( &waiter );

    for ( int i = 0; i < numTries; ++i )
    {
        for ( int j = 0; j < numWaiters; ++j )
        {
            synchronized( mutex )
            {
                ++numReady;
                condReady.notify();
            }
        }
        while ( true )
        {
            synchronized( synLoop )
            {
                if ( numDone >= numWaiters )
                    break;
            }
            Thread.yield();
        }
        for ( int j = 0; j < numWaiters; ++j )
        {
            semDone.notify();
        }
    }

    group.joinAll();
    writeln(numTotal); // numWaiters * numTries
}


void testNotifyAll()
{
    auto mutex      = new Mutex;
    auto condReady  = new Condition( mutex );
    int  numWaiters = 10;
    int  numReady   = 0;
    int  numDone    = 0;
    bool alert      = false;

    void waiter()
    {
        synchronized( mutex )
        {
            ++numReady;
            while ( !alert )
                condReady.wait();
            ++numDone;
        }
    }

    auto group = new ThreadGroup;

    for ( int i = 0; i < numWaiters; ++i )
        group.create( &waiter );

    while ( true )
    {
        synchronized( mutex )
        {
            if ( numReady >= numWaiters )
            {
                alert = true;
                condReady.notifyAll();
                break;
            }
        }
        Thread.yield();
    }
    group.joinAll();
    assert( numReady == numWaiters && numDone == numWaiters );
}


void testWaitTimeout()
{
    auto mutex      = new Mutex;
    auto condReady  = new Condition( mutex );
    bool waiting    = false;
    bool alertedOne = true;
    bool alertedTwo = true;

    void waiter()
    {
        synchronized( mutex )
        {
            waiting    = true;
            // we never want to miss the notification (30s)
            alertedOne = condReady.wait( dur!"seconds"(30) );
            // but we don't want to wait long for the timeout (10ms)
            alertedTwo = condReady.wait( dur!"msecs"(10) );
        }
    }

    auto thread = new Thread( &waiter );
    thread.start();

    while ( true )
    {
        synchronized( mutex )
        {
            if ( waiting )
            {
                condReady.notify();
                break;
            }
        }
        Thread.yield();
    }
    thread.join();
    assert( waiting );
    assert( alertedOne );
    assert( !alertedTwo );
}

testNotify();
testNotifyAll();
testWaitTimeout();

Authors

Sean Kelly

License

Boost License 1.0