public void CannotWriteWhileWriting()
{
using (var x = new ReadWriteLock())
{
var ok = true;
var doneThread = false;
using (x.EnterWrite())
{
Assert.IsTrue(x.IsCurrentThreadWriter);
var a = new Thread
(
() =>
{
IDisposable engagement = null;
try
{
ok &= !x.TryEnterWrite(out engagement);
}
finally
{
if (engagement != null)
{
engagement.Dispose();
}
doneThread = true;
}
}
);
a.Start();
a.Join();
}
Assert.IsTrue(ok);
Assert.IsTrue(doneThread);
}
}
public void CanKnowIsWriter()
{
// ReadWriteLock always able to tell if a therad is the writer
using (var x = new ReadWriteLock(true))
{
Assert.IsFalse(x.HasWriter);
using (x.EnterWrite())
{
Assert.IsTrue(x.IsCurrentThreadWriter);
Assert.IsTrue(x.HasWriter);
}
// Not Reentrant ReadWriteLock is not
using (var y = new ReadWriteLock(false))
{
Assert.IsFalse(y.HasWriter);
using (y.EnterWrite())
{
Assert.IsTrue(y.IsCurrentThreadWriter);
Assert.IsTrue(y.HasWriter);
}
// ReadWriteLock is not reentrant by default
using (var z = new ReadWriteLock())
{
Assert.IsFalse(z.HasWriter);
using (z.EnterWrite())
{
Assert.IsTrue(z.IsCurrentThreadWriter);
Assert.IsTrue(z.HasWriter);
}
}
}
}
}
public void ReentryReadToWriteRaceCondition()
{
using (var w = new ManualResetEvent(false))
{
using (var x = new ReadWriteLock(true))
{
var enterCount = 0;
var doneCount = 0;
var errorCount = 0;
var successCount = 0;
ThreadStart tmp = () =>
{
using (x.EnterRead())
{
Interlocked.Increment(ref enterCount);
w.WaitOne();
// If a thread is a reader it can become a writer as long as there are no other readers
// When we have multiple readers trying to become a writer...
try
{
// write mode is requested and reserved by one thread - others fail
using (x.EnterWrite())
{
Interlocked.Increment(ref successCount);
}
}
catch (InvalidOperationException)
{
Interlocked.Increment(ref errorCount);
}
}
Interlocked.Increment(ref doneCount);
};
var threads = new Thread[5];
for (var index = 0; index < 5; index++)
{
threads[index] = new Thread(tmp);
}
for (var index = 0; index < 5; index++)
{
threads[index].Start();
}
do
{
Thread.Sleep(10);
} while (enterCount < 5);
w.Set();
for (var index = 0; index < 5; index++)
{
threads[index].Join();
}
Assert.AreEqual(5, doneCount);
Assert.AreEqual(1, successCount); // One succeds - the thread that succeds to reserve write waits for others to leave
Assert.AreEqual(4, errorCount); // The others get InvalidOperationException - the threads that fail the reserve fail
} // This code results in a dead lock in a not reentrant ReadWriteLock
}
}
public void CanEnterWrite()
{
var x = new ReadWriteLock();
using (x.EnterWrite())
{
Assert.IsTrue(x.IsCurrentThreadWriter);
}
}
public void WriteWaitsMultipleReadsToFinish() // TODO: Review
{
using (var w0 = new ManualResetEvent(false))
{
using (var w1 = new ManualResetEvent(false))
{
using (var x = new ReadWriteLock())
{
var ok = false;
int[] z = { 0 };
var threads = new Thread[5];
for (var index = 0; index < 5; index++)
{
threads[index] = new Thread
(
() =>
{
w0.WaitOne();
using (x.EnterRead())
{
w1.Set();
Interlocked.Increment(ref z[0]);
Thread.Sleep(10);
}
}
);
}
var a = new Thread
(
() =>
{
w1.WaitOne();
using (x.EnterWrite())
{
Assert.IsTrue(x.IsCurrentThreadWriter);
ok = Interlocked.Increment(ref z[0]) == 6;
}
}
);
for (var index = 0; index < 5; index++)
{
threads[index].Start();
}
a.Start();
w0.Set();
for (var index = 0; index < 5; index++)
{
threads[index].Join();
}
a.Join();
Assert.IsTrue(ok);
Assert.AreEqual(7, Interlocked.Increment(ref z[0]));
}
}
}
}
public void CanReentryWriteToRead()
{
var x = new ReadWriteLock();
using (x.EnterWrite())
{
// If a thread is a writer it can be also a reader
using (x.EnterRead())
{
}
}
}
public void CannotReentryReadToWriteWhenThereAreMoreReaders()
{
using (var w1 = new ManualResetEvent(false))
{
using (var w2 = new ManualResetEvent(false))
{
using (var x = new ReadWriteLock(true))
{
var ok = true;
var a = new Thread
(
() =>
{
using (x.EnterRead())
{
w2.Set();
w1.WaitOne();
}
}
);
a.Start();
w2.WaitOne();
using (x.EnterRead())
{
Assert.IsFalse(x.IsCurrentThreadWriter);
IDisposable engagement = null;
try
{
ok &= !x.TryEnterWrite(out engagement);
}
finally
{
if (engagement != null)
{
engagement.Dispose();
}
}
}
w1.Set();
a.Join();
using (x.EnterRead())
{
using (x.EnterWrite())
{
Assert.IsTrue(x.IsCurrentThreadWriter);
Assert.IsTrue(ok);
}
}
} // This code results in a dead lock in a not reentrant ReadWriteLock
}
}
}
public void CanReentryReadToWrite()
{
var x = new ReadWriteLock(true); // This code results in a dead lock in a not reentrant ReadWriteLock
using (x.EnterRead())
{
Assert.IsFalse(x.IsCurrentThreadWriter);
// If a thread is a reader it can become a writer as long as there are no other readers
using (x.EnterWrite())
{
Assert.IsTrue(x.IsCurrentThreadWriter);
}
}
}
public void WriteWaitsReadToFinish()
{
using (var w = new ManualResetEvent(false))
{
using (var x = new ReadWriteLock())
{
int[] z = { 0 };
var ok = true;
var a = new Thread
(
() =>
{
w.WaitOne();
using (x.EnterWrite())
{
ok = ok && Interlocked.Increment(ref z[0]) == 2;
}
}
);
var b = new Thread
(
() =>
{
using (x.EnterRead())
{
w.Set();
Thread.Sleep(10);
ok = ok && Interlocked.Increment(ref z[0]) == 1;
}
}
);
a.Start();
b.Start();
a.Join();
b.Join();
Assert.IsTrue(ok);
Assert.AreEqual(3, Interlocked.Increment(ref z[0]));
}
}
}
public void OnlyOneWriterAtTheTime()
{
using (var w = new ManualResetEvent(false))
{
using (var x = new ReadWriteLock())
{
int[] z = { 0 };
var ok = true;
var threads = new Thread[5];
for (var index = 0; index < 5; index++)
{
threads[index] = new Thread
(
() =>
{
w.WaitOne();
using (x.EnterWrite())
{
var got = Interlocked.Increment(ref z[0]);
Thread.Sleep(10);
ok = ok && Interlocked.Increment(ref z[0]) == got + 1;
}
}
);
}
for (var index = 0; index < 5; index++)
{
threads[index].Start();
}
w.Set();
for (var index = 0; index < 5; index++)
{
threads[index].Join();
}
Assert.IsTrue(ok);
Assert.AreEqual(11, Interlocked.Increment(ref z[0]));
}
}
}
public void OnlyOneWriterAtTheTimeEx() // TODO: Review - race condition
{
using (var w = new ManualResetEvent(false))
{
using (var x = new ReadWriteLock())
{
var doneThread = 0;
var ok = true;
ThreadStart tmp = () =>
{
w.WaitOne();
IDisposable engagementA = null;
try
{
ok &= !x.TryEnterWrite(out engagementA);
}
finally
{
if (engagementA != null)
{
engagementA.Dispose();
}
Interlocked.Increment(ref doneThread);
}
};
var a = new Thread(tmp);
using (x.EnterWrite())
{
a.Start();
w.Set();
Thread.Sleep(10);
}
a.Join();
Assert.IsTrue(ok);
Assert.AreEqual(1, doneThread);
var b = new Thread(tmp);
IDisposable engagementB = null;
try
{
if (x.TryEnterWrite(out engagementB))
{
Assert.IsTrue(x.IsCurrentThreadWriter);
b.Start();
w.Set();
b.Join();
}
else
{
Assert.Fail();
}
}
finally
{
if (engagementB != null)
{
engagementB.Dispose();
}
}
Assert.IsTrue(ok);
Assert.AreEqual(2, doneThread);
}
}
}
public void WriteWaitsMultipleReadsToFinish()
{
using (var w0 = new ManualResetEvent(false))
{
using (var w1 = new ManualResetEvent(false))
{
using (var x = new ReadWriteLock())
{
int[] z = { 0, 0 };
var foundReaders = -1;
var ok = false;
var threads = new Thread[5];
for (var index = 0; index < 5; index++)
{
threads[index] = new Thread
(
() =>
{
w0.WaitOne();
using (x.EnterRead())
{
Interlocked.Increment(ref z[1]);
w1.Set();
Interlocked.Increment(ref z[0]);
Thread.Sleep(10);
Interlocked.Decrement(ref z[1]);
}
}
);
}
var a = new Thread
(
() =>
{
w1.WaitOne();
using (x.EnterWrite())
{
foundReaders = Volatile.Read(ref z[1]);
ok = x.IsCurrentThreadWriter;
Interlocked.Increment(ref z[0]);
}
}
);
for (var index = 0; index < 5; index++)
{
threads[index].Start();
}
a.Start();
w0.Set();
for (var index = 0; index < 5; index++)
{
threads[index].Join();
}
a.Join();
Assert.IsTrue(ok);
Assert.AreEqual(0, foundReaders);
Assert.AreEqual(7, Interlocked.Increment(ref z[0]));
}
}
}
}