[HTTP/3] HttpConnectionPool may leak authorityExpireTimer / hit ObjectDisposedException

[MihaZupan]

Based on code inspection.

HttpConnectionPool.HandleAltSvc may create a Timer if Dispose runs during/before it, and it will never be disposed.
The method should check _disposed in this branch (while holding the lock), before creating a new Timer:

runtime/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionPool.cs

Lines 1155 to 1156 in a1bc0f3

	if (_authorityExpireTimer == null)
	{

The good news is that the timer won't root the HttpConnectionPool instance, but the timer entry may remain queued for a month.

A related issue is that the same method will also access the _authorityExpireTimer outside a lock a few lines above, which could lead to an unexpected ObjectDisposedException leaking out:

runtime/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionPool.cs

Line 1112 in a1bc0f3

_authorityExpireTimer.Change(Timeout.Infinite, Timeout.Infinite);

Tagging subscribers to this area: @dotnet/ncl
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Based on code inspection.

HttpConnectionPool.HandleAltSvc may create a Timer if Dispose runs during/before it.
The method should check _disposed in this branch (while holding the lock), before creating a new Timer:

runtime/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionPool.cs

Lines 1155 to 1156 in a1bc0f3

	if (_authorityExpireTimer == null)
	{

The good news is that the timer won't root the HttpConnectionPool instance, but the timer entry may remain queued for a month.

A related issue is that the same method will also access the _authorityExpireTimer outside a lock a few lines above, which could lead to an unexpected ObjectDisposedException leaking out:

runtime/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionPool.cs

Line 1112 in a1bc0f3

_authorityExpireTimer.Change(Timeout.Infinite, Timeout.Infinite);

Author:	MihaZupan
Assignees:	-
Labels:	bug, area-System.Net.Http
Milestone:	-

[MihaZupan]

Looks like this AltSvc logic around the blocklist is also racy.
Tasks may not be canceled or you may try using a disposed CTS.

In this case, the whole HttpConnectionPool is gonna be rooted by the 10 minute timer.

[karelz]

Triage: Affects HTTP/3, reliability - race condition. We should fix it in 7.0.