This class represents a mutex that allows any number of readers to enter,
but when a writer enters, all other readers and writers are blocked.
Please note that this mutex is not recursive and is intended to guard access
to data only. Also, no deadlock checking is in place because doing so would
require dynamic memory allocation, which would reduce performance by an
unacceptable amount. As a result, any attempt to recursively acquire this
mutex may well deadlock the caller, particularly if a write lock is acquired
while holding a read lock, or vice-versa. In practice, this should not be
an issue however, because it is uncommon to call deeply into unknown code
while holding a lock that simply protects data.
Constructors
Name | Description |
this
(policy)
|
Initializes a read/write mutex object with the supplied policy.
|
Methods
Name | Description |
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.
|
Inner classes
Name | Description |
Reader
|
This class can be considered a mutex in its own right, and is used to
negotiate a read lock for the enclosing mutex.
|
Writer
|
This class can be considered a mutex in its own right, and is used to
negotiate a write lock for the enclosing mutex.
|
Enums
Name | Description |
Policy
|
Defines the policy used by this mutex. Currently, two policies are
defined.
|
Example
import core.atomic, core.thread, core.sync.semaphore;
static void runTest(ReadWriteMutex.Policy policy)
{
scope mutex = new ReadWriteMutex(policy);
scope rdSemA = new Semaphore, rdSemB = new Semaphore,
wrSemA = new Semaphore, wrSemB = new Semaphore;
shared size_t numReaders, numWriters;
void readerFn()
{
synchronized (mutex.reader)
{
atomicOp!"+="(numReaders, 1);
rdSemA.notify();
rdSemB.wait();
atomicOp!"-="(numReaders, 1);
}
}
void writerFn()
{
synchronized (mutex.writer)
{
atomicOp!"+="(numWriters, 1);
wrSemA.notify();
wrSemB.wait();
atomicOp!"-="(numWriters, 1);
}
}
void waitQueued(size_t queuedReaders, size_t queuedWriters)
{
for (;;)
{
synchronized (mutex.m_commonMutex)
{
if (mutex.m_numQueuedReaders == queuedReaders &&
mutex.m_numQueuedWriters == queuedWriters)
break;
}
Thread.yield();
}
}
scope group = new ThreadGroup;
// 2 simultaneous readers
group.create(&readerFn); group.create(&readerFn);
rdSemA.wait(); rdSemA.wait();
writeln(numReaders); // 2
rdSemB.notify(); rdSemB.notify();
group.joinAll();
writeln(numReaders); // 0
foreach (t; group) group.remove(t);
// 1 writer at a time
group.create(&writerFn); group.create(&writerFn);
wrSemA.wait();
assert(!wrSemA.tryWait());
writeln(numWriters); // 1
wrSemB.notify();
wrSemA.wait();
writeln(numWriters); // 1
wrSemB.notify();
group.joinAll();
writeln(numWriters); // 0
foreach (t; group) group.remove(t);
// reader and writer are mutually exclusive
group.create(&readerFn);
rdSemA.wait();
group.create(&writerFn);
waitQueued(0, 1);
assert(!wrSemA.tryWait());
assert(numReaders == 1 && numWriters == 0);
rdSemB.notify();
wrSemA.wait();
assert(numReaders == 0 && numWriters == 1);
wrSemB.notify();
group.joinAll();
assert(numReaders == 0 && numWriters == 0);
foreach (t; group) group.remove(t);
// writer and reader are mutually exclusive
group.create(&writerFn);
wrSemA.wait();
group.create(&readerFn);
waitQueued(1, 0);
assert(!rdSemA.tryWait());
assert(numReaders == 0 && numWriters == 1);
wrSemB.notify();
rdSemA.wait();
assert(numReaders == 1 && numWriters == 0);
rdSemB.notify();
group.joinAll();
assert(numReaders == 0 && numWriters == 0);
foreach (t; group) group.remove(t);
// policy determines whether queued reader or writers progress first
group.create(&writerFn);
wrSemA.wait();
group.create(&readerFn);
group.create(&writerFn);
waitQueued(1, 1);
assert(numReaders == 0 && numWriters == 1);
wrSemB.notify();
if (policy == ReadWriteMutex.Policy.PREFER_READERS)
{
rdSemA.wait();
assert(numReaders == 1 && numWriters == 0);
rdSemB.notify();
wrSemA.wait();
assert(numReaders == 0 && numWriters == 1);
wrSemB.notify();
}
else if (policy == ReadWriteMutex.Policy.PREFER_WRITERS)
{
wrSemA.wait();
assert(numReaders == 0 && numWriters == 1);
wrSemB.notify();
rdSemA.wait();
assert(numReaders == 1 && numWriters == 0);
rdSemB.notify();
}
group.joinAll();
assert(numReaders == 0 && numWriters == 0);
foreach (t; group) group.remove(t);
}
runTest(ReadWriteMutex.Policy.PREFER_READERS);
runTest(ReadWriteMutex.Policy.PREFER_WRITERS);