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Fixes "messages get sent out-of-order when a backlog is created by another thread" #1779

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Merged
mgravell merged 2 commits into from
Jul 1, 2021
Merged

Fixes "messages get sent out-of-order when a backlog is created by another thread" #1779

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ee380d3
Revert "More reverts" to reapply the fix to #1719.
TimLovellSmith Jun 21, 2021
72f31d0
Merge branch 'main' into fix1719
NickCraver Jun 22, 2021
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17 changes: 17 additions & 0 deletions src/StackExchange.Redis/PhysicalBridge.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -701,6 +701,14 @@ internal WriteResult WriteMessageTakingWriteLockSync(PhysicalConnection physical
Trace("Writing: " + message);
message.SetEnqueued(physical); // this also records the read/write stats at this point

// AVOID REORDERING MESSAGES
// Prefer to add it to the backlog if this thread can see that there might already be a message backlog.
// We do this before attempting to take the writelock, because we won't actually write, we'll just let the backlog get processed in due course
if (PushToBacklog(message, onlyIfExists: true))
{
return WriteResult.Success; // queued counts as success
}

LockToken token = default;
try
{
Expand Down Expand Up @@ -978,11 +986,20 @@ internal ValueTask<WriteResult> WriteMessageTakingWriteLockAsync(PhysicalConnect
Trace("Writing: " + message);
message.SetEnqueued(physical); // this also records the read/write stats at this point

// AVOID REORDERING MESSAGES
// Prefer to add it to the backlog if this thread can see that there might already be a message backlog.
// We do this before attempting to take the writelock, because we won't actually write, we'll just let the backlog get processed in due course
if (PushToBacklog(message, onlyIfExists: true))
{
return new ValueTask<WriteResult>(WriteResult.Success); // queued counts as success
}

bool releaseLock = true; // fine to default to true, as it doesn't matter until token is a "success"
int lockTaken = 0;
LockToken token = default;
try
{

// try to acquire it synchronously
// note: timeout is specified in mutex-constructor
token = _singleWriterMutex.TryWait(options: WaitOptions.NoDelay);
Expand Down