private LockCookie EnterSlow()
{
// Attempt to steal the ownership. Take a regular lock to ensure that only one thread is trying to steal it at a time.
lock (this)
{
// We are the new fast thread now!
var oldEntry = _current;
_current = new LockCookie(Environment.CurrentManagedThreadId);
// After MemoryBarrierProcessWide, we can be sure that the Volatile.Read done by the fast thread will see that it is not a fast
// thread anymore, and thus it will not attempt to enter the lock.
Interlocked.MemoryBarrierProcessWide();
// Keep looping as long as the lock is taken by other thread
SpinWait sw = new SpinWait();
while (oldEntry.Taken)
{
sw.SpinOnce();
}
// We have seen that the other thread released the lock by setting Taken to false.
// However, on platforms with weak memory ordering (ex: ARM32, ARM64) observing that does not guarantee that the writes executed by that
// thread prior to releasing the lock are all committed to the shared memory.
// We could fix that by doing the release via Volatile.Write, but we do not want to add expense to every release on the fast path.
// Instead we will do another MemoryBarrierProcessWide here.
// NOTE: not needed on x86/x64
Interlocked.MemoryBarrierProcessWide();
_current.Taken = true;
return(_current);
}
}
private LockCookie EnterSlow()
{
// Attempt to steal the ownership. Take a regular lock to ensure that only one thread is trying to steal it at a time.
lock (this)
{
// We are the new fast thread now!
var oldEntry = _current;
_current = new LockCookie(Environment.CurrentManagedThreadId);
// MemoryBarrierProcessWide ensures, process-wide, that our write to _current becomes visible
// to every thread, and all writes by other threads become visible to us before we can continue.
// As a result any other thread that sets Taken to true either:
// a) made it past the read of _current and owns the lock OR
// b) will see that _current has changed and will revert Taken without taking the lock
// Thus we only need to wait for 'Taken' to become false and claim the lock for ourselves.
// 'Taken' may yet switch to true after that, but that cannot result in other thread owning the lock.
Interlocked.MemoryBarrierProcessWide();
// Keep looping as long as the lock is taken by other thread
SpinWait sw = new SpinWait();
while (oldEntry.Taken)
{
sw.SpinOnce();
}
_current.Taken = true;
return(_current);
}
}
public async Task HandleDisconnectedAsync(MqttClientDisconnectedEventArgs eventArgs)
{
_connected = false;
Interlocked.MemoryBarrierProcessWide();
if (!(_client is null) && eventArgs.ReasonCode != MqttClientDisconnectReason.AdministrativeAction && !_connected)
{
_logger.LogWarning(eventArgs.Exception, "MQTT client has disconnected, reason: {0}, trying to reconnect.", eventArgs.ReasonCode);
await DoConnectAsync(_client, CancellationToken.None);
}
}
static void Test1()
{
x = 1;
// CPU has the ability to reorder the code instructions, if the codes have no dependencies
// like there Test1 and Test has no dependencies, so CPU can run Test1 and Test2 in any order
// use MemoryBarrierProcessWide to block any CPU
// or use Interlocked.MemoryBarrier() in both Test 1 and Test2
Interlocked.MemoryBarrierProcessWide();
a = y;
}
void Update(ILogger newRoot, ILogger newCached, bool frozen)
{
_root = newRoot;
_cached = newCached;
_frozen = frozen;
// https://github.com/dotnet/runtime/issues/20500#issuecomment-284774431
// Publish `_cached` and `_frozen`. This is useful here because it means that once the logger is frozen - which
// we always expect - reads don't require any synchronization/interlocked instructions.
Interlocked.MemoryBarrierProcessWide();
}
public Logger Freeze()
{
lock (_sync)
{
if (_frozen)
{
throw new InvalidOperationException("The logger is already frozen.");
}
_frozen = true;
// https://github.com/dotnet/runtime/issues/20500#issuecomment-284774431
// Publish `_logger` and `_frozen`. This is useful here because it means that once the logger is frozen - which
// we always expect - reads don't require any synchronization/interlocked instructions.
Interlocked.MemoryBarrierProcessWide();
return(_logger);
}
}
private static void InterlockedOperations()
{
//_counter becomes 1
Interlocked.Increment(ref _counter);
// _counter becomes 0
Interlocked.Decrement(ref _counter);
// Add: _counter becomes 2
Interlocked.Add(ref _counter, 2);
//Subtract: _counter becomes 0
Interlocked.Add(ref _counter, -2);
// Reads 64 bit field
Console.WriteLine(Interlocked.Read(ref _counter));
// Swaps _counter value with 10
Console.WriteLine(Interlocked.Exchange(ref _counter, 10));
//Checks if _counter is 10 and if yes replace with 100
Console.WriteLine(Interlocked.CompareExchange(ref _counter, 100, 10)); // _counter becomes 100
Interlocked.MemoryBarrier();
Interlocked.MemoryBarrierProcessWide();
}
private LockCookie EnterSlow()
{
// Attempt to steal the ownership. Take a regular lock to ensure that only one thread is trying to steal it at a time.
lock (this)
{
// We are the new fast thread now!
var oldEntry = _current;
_current = new LockCookie(Environment.CurrentManagedThreadId);
// After MemoryBarrierProcessWide, we can be sure that the Volatile.Read done by the fast thread will see that it is not a fast
// thread anymore, and thus it will not attempt to enter the lock.
Interlocked.MemoryBarrierProcessWide();
// Keep looping as long as the lock is taken by other thread
SpinWait sw = new SpinWait();
while (oldEntry.Taken)
{
sw.SpinOnce();
}
_current.Taken = true;
return(_current);
}
}
static void Test1()
{
x = 1;
Interlocked.MemoryBarrierProcessWide();
a = y;
}
private static void BarrierUsingInterlockedProcessWideBarrier()
{
b = c;
Interlocked.MemoryBarrierProcessWide();
a = 1;
}