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fix: 1 mili sec delay for read and write #128418

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fix: 1 mili sec delay for read and write #128418

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47 changes: 34 additions & 13 deletions src/libraries/System.IO.Ports/src/System/IO/Ports/SerialStream.Unix.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -787,11 +787,13 @@ private unsafe int ProcessRead(SerialStreamIORequest r)
{
Interop.ErrorInfo lastError = Interop.Sys.GetLastErrorInfo();

// ignore EWOULDBLOCK since we handle timeout elsewhere
if (lastError.Error != Interop.Error.EWOULDBLOCK)
if (lastError.Error == Interop.Error.EWOULDBLOCK)
{
readRequest.Complete(Interop.GetIOException(lastError));
// no data available right now, signal caller to stop draining
return -1;
}

readRequest.Complete(Interop.GetIOException(lastError));
}
else if (numBytes > 0)
{
Expand Down Expand Up @@ -820,9 +822,13 @@ private unsafe int ProcessWrite(SerialStreamIORequest r)
{
Interop.ErrorInfo lastError = Interop.Sys.GetLastErrorInfo();

// ignore EWOULDBLOCK since we handle timeout elsewhere
// numBytes == 0 means that there might be an error
if (lastError.Error != Interop.Error.SUCCESS && lastError.Error != Interop.Error.EWOULDBLOCK)
if (lastError.Error == Interop.Error.EWOULDBLOCK)
{
// write buffer full right now, signal caller to stop draining
return -1;
}

if (lastError.Error != Interop.Error.SUCCESS)
{
r.Complete(Interop.GetIOException(lastError));
}
Expand Down Expand Up @@ -850,7 +856,12 @@ private static int DoIORequest(Queue<SerialStreamIORequest> q, object queueLock,
while (TryPeekNextRequest(out SerialStreamIORequest r))
{
int ret = op(r);
Debug.Assert(ret >= 0);

if (ret < 0)
{
// EWOULDBLOCK — no data available right now, propagate to caller
return -1;
}

if (r.IsCompleted)
{
Expand Down Expand Up @@ -947,9 +958,9 @@ private void IOLoop()
else
{
Interop.PollEvents events = PollEvents(1,
pollReadEvents: hasPendingReads,
pollWriteEvents: hasPendingWrites,
out Interop.ErrorInfo? error);
pollReadEvents: hasPendingReads,
pollWriteEvents: hasPendingWrites,
out Interop.ErrorInfo? error);

if (error.HasValue)
{
Expand All @@ -967,13 +978,23 @@ private void IOLoop()

if (events.HasFlag(Interop.PollEvents.POLLIN))
{
int bytesRead = DoIORequest(_readQueue, _readQueueLock, _processReadDelegate);
_totalBytesRead += bytesRead;
// drain all requests that have data ready right now
// without paying another 1ms poll cost per request
while (!IsReadQueueEmpty())
{
int bytesRead = DoIORequest(_readQueue, _readQueueLock, _processReadDelegate);
if (bytesRead <= 0) break; // 0 = queue empty, -1 = EWOULDBLOCK
_totalBytesRead += bytesRead;
}
}

if (events.HasFlag(Interop.PollEvents.POLLOUT))
{
DoIORequest(_writeQueue, _writeQueueLock, _processWriteDelegate);
// flush as many pending write requests as possible
while (!IsWriteQueueEmpty())
{
if (DoIORequest(_writeQueue, _writeQueueLock, _processWriteDelegate) <= 0) break;
}
}
}

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