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The mutex module provides a primitive for maintaining mutually exclusive access.
Sean Kelly

Source: core/sync/mutex.d

class Mutex: object.Object.Monitor;
This class represents a general purpose, recursive mutex.
auto mutex      = new Mutex;
int  numThreads = 10;
int  numTries   = 1000;
int  lockCount  = 0;

void testFn()
    for( int i = 0; i < numTries; ++i )
        synchronized( mutex )

auto group = new ThreadGroup;

for( int i = 0; i < numThreads; ++i )
    group.create( &testFn );

assert( lockCount == numThreads * numTries );
nothrow @trusted this();
Initializes a mutex object.
SyncError on error.
nothrow @trusted this(Object o);
Initializes a mutex object and sets it as the monitor for o.

In: o must not already have a monitor.

@trusted void lock();
If this lock is not already held by the caller, the lock is acquired, then the internal counter is incremented by one.
SyncError on error.
@trusted void unlock();
Decrements the internal lock count by one. If this brings the count to zero, the lock is released.
SyncError on error.
bool tryLock();
If the lock is held by another caller, the method returns. Otherwise, the lock is acquired if it is not already held, and then the internal counter is incremented by one.
SyncError on error.
true if the lock was acquired and false if not.