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pyreferencedecrementer.cs
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using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Diagnostics;
using System.Threading;
using System.Threading.Tasks;
namespace Python.Runtime
{
/// <summary>
/// Background python objects reference decrementer.
/// !!! By some unknown reasons python references decrements have been performed in the GC thread - affects GC. !!!
/// This component contains background thread with the queue of IntPtr python object references.
/// Finalizers should schedule reference decrement operation in this component to avoid problem with GC.
/// Each PythonEngine Init/Shutdown have it's own PyReferenceDecrementer, so PyObject should also have a field with the
/// reference to the correct PyReferenceDecrementer.
/// </summary>
internal class PyReferenceDecrementer : IDisposable
{
private static readonly DedicatedThreadTaskScheduler DedicatedThreadTaskScheduler = new DedicatedThreadTaskScheduler();
private readonly BlockingCollection<IntPtr> _asyncDecRefQueue = new BlockingCollection<IntPtr>();
private CancellationTokenSource _cts;
private CancellationToken _ct;
private Task _backgroundWorkerTask;
public PyReferenceDecrementer()
{
InitDecRefThread();
}
public void ScheduleDecRef(IntPtr pyRef)
{
// ReSharper disable once MethodSupportsCancellation
_asyncDecRefQueue.Add(pyRef);
}
internal void WaitForPendingDecReferences()
{
ShutdownDecRefThread();
InitDecRefThread();
}
private void ShutdownDecRefThread()
{
_cts?.Cancel();
try
{
IntPtr ts = IntPtr.Zero;
if (Runtime.PyGILState_GetThisThreadState() != IntPtr.Zero)
{
ts = Runtime.PyEval_SaveThread();
}
try
{
// ReSharper disable once MethodSupportsCancellation
_backgroundWorkerTask.Wait();
}
catch (AggregateException ex)
{
if (!(ex.InnerException is OperationCanceledException))
{
throw;
}
}
finally
{
if (ts != IntPtr.Zero)
{
Runtime.PyEval_RestoreThread(ts);
}
}
}
catch
{
// Just stopping background thread.
}
_cts = null;
_ct = default(CancellationToken);
_backgroundWorkerTask = null;
}
private void InitDecRefThread()
{
_cts = new CancellationTokenSource();
_ct = _cts.Token;
_backgroundWorkerTask = Task.Factory.StartNew(WorkerThread, _ct, TaskCreationOptions.LongRunning,
DedicatedThreadTaskScheduler);
}
private void WorkerThread()
{
while (true)
{
IntPtr refToDecrease = _asyncDecRefQueue.Take(_ct); ;
try
{
IntPtr gs = PythonEngine.AcquireLock();
try
{
do
{
Runtime.XDecref(refToDecrease);
} while (_asyncDecRefQueue.TryTake(out refToDecrease));
}
finally
{
PythonEngine.ReleaseLock(gs);
}
}
catch
{
// Nothing to do in this case.
}
}
}
public void Dispose()
{
ShutdownDecRefThread();
}
}
/// <summary>
/// Scheduler that uses only one thread for all scheduled task.
/// </summary>
internal class DedicatedThreadTaskScheduler : TaskScheduler
{
private readonly BlockingCollection<Task> _queuedTasks = new BlockingCollection<Task>();
/// <summary>
/// Initializes a new instance of the <see cref="DedicatedThreadTaskScheduler"/> class.
/// </summary>
public DedicatedThreadTaskScheduler()
{
var thread = new Thread(WorkerThreadProc);
thread.IsBackground = true;
thread.Start();
}
/// <inheritdoc/>
protected override IEnumerable<Task> GetScheduledTasks()
{
return _queuedTasks;
}
/// <inheritdoc/>
protected override void QueueTask(Task task)
{
_queuedTasks.Add(task);
}
/// <inheritdoc/>
protected override bool TryExecuteTaskInline(Task task, bool taskWasPreviouslyQueued)
{
return false;
}
private void WorkerThreadProc()
{
for (;;)
{
Task dequeuedTask = _queuedTasks.Take();
// This is synchronous execution.
bool taskExecuted = TryExecuteTask(dequeuedTask);
Debug.Assert(taskExecuted, "DedicatedThread task have some problem.");
}
}
}
}