Exceptions: include Timer.ActiveCount in .NET Core stats (#2500)

We're seeing some instances of quite delayed timeouts and at least in two deeper investigations it was due to a huge number of timers firing and the backlog timeout assessment timer not triggering for an extended period of time. To help users diagnose this, adding the cheap counter to the .NET Core pool stats where `Timer.ActiveCount` is readily available.

This is available in all the .NET (non-Framework) versions we support.

Before:
> ...POOL: (Threads=25,QueuedItems=0,CompletedItems=1066)

After:
> ...POOL: (Threads=25,QueuedItems=0,CompletedItems=1066,Timers=46)

See #2477 for another possible instance of this.

Author: NickCraver

docs/ReleaseNotes.md

@@ -10,6 +10,7 @@ Current package versions:
 
 - Change: Target net6.0 instead of net5.0, since net5.0 is end of life. ([#2497 by eerhardt](https://github.com/StackExchange/StackExchange.Redis/pull/2497))
 - Fix: Fix nullability annotation of IConnectionMultiplexer.RegisterProfiler ([#2494 by eerhardt](https://github.com/StackExchange/StackExchange.Redis/pull/2494))
+- Add: `Timer.ActiveCount` under `POOL` in timeout messages on .NET 6+ to help diagnose timer overload affecting timeout evaluations ([#2500 by NickCraver](https://github.com/StackExchange/StackExchange.Redis/pull/2500))
 
 ## 2.6.116
 

src/StackExchange.Redis/PerfCounterHelper.cs

@@ -23,7 +23,7 @@ internal static int GetThreadPoolStats(out string iocp, out string worker, out s
             worker = $"(Busy={busyWorkerThreads},Free={freeWorkerThreads},Min={minWorkerThreads},Max={maxWorkerThreads})";
 
 #if NETCOREAPP
-            workItems = $"(Threads={ThreadPool.ThreadCount},QueuedItems={ThreadPool.PendingWorkItemCount},CompletedItems={ThreadPool.CompletedWorkItemCount})";
+            workItems = $"(Threads={ThreadPool.ThreadCount},QueuedItems={ThreadPool.PendingWorkItemCount},CompletedItems={ThreadPool.CompletedWorkItemCount},Timers={Timer.ActiveCount})";
 #else
             workItems = null;
 #endif

tests/StackExchange.Redis.Tests/AbortOnConnectFailTests.cs

@@ -16,7 +16,7 @@ public void NeverEverConnectedNoBacklogThrowsConnectionNotAvailableSync()
         var db = conn.GetDatabase();
         var key = Me();
 
-        // No connection is active/available to service this operation: GET 6.0.14AbortOnConnectFailTests-NeverEverConnectedThrowsConnectionNotAvailable; UnableToConnect on doesnot.exist.0d034c26350e4ee199d6c5f385a073f7:6379/Interactive, Initializing/NotStarted, last: NONE, origin: BeginConnectAsync, outstanding: 0, last-read: 0s ago, last-write: 0s ago, keep-alive: 500s, state: Connecting, mgr: 10 of 10 available, last-heartbeat: never, global: 0s ago, v: 2.6.99.22667, mc: 1/1/0, mgr: 10 of 10 available, clientName: NAMISTOU-3(SE.Redis-v2.6.99.22667), IOCP: (Busy=0,Free=1000,Min=32,Max=1000), WORKER: (Busy=2,Free=32765,Min=32,Max=32767), POOL: (Threads=17,QueuedItems=0,CompletedItems=20), v: 2.6.99.22667
+        // No connection is active/available to service this operation: GET 6.0.18AbortOnConnectFailTests-NeverEverConnectedNoBacklogThrowsConnectionNotAvailableSync; UnableToConnect on doesnot.exist.d4d1424806204b68b047954b1db3411d:6379/Interactive, Initializing/NotStarted, last: NONE, origin: BeginConnectAsync, outstanding: 0, last-read: 0s ago, last-write: 0s ago, keep-alive: 100s, state: Connecting, mgr: 4 of 10 available, last-heartbeat: never, global: 0s ago, v: 2.6.120.51136, mc: 1/1/0, mgr: 5 of 10 available, clientName: CRAVERTOP7(SE.Redis-v2.6.120.51136), IOCP: (Busy=0,Free=1000,Min=16,Max=1000), WORKER: (Busy=3,Free=32764,Min=16,Max=32767), POOL: (Threads=25,QueuedItems=0,CompletedItems=1066,Timers=46), v: 2.6.120.51136
         var ex = Assert.Throws<RedisConnectionException>(() => db.StringGet(key));
         Log("Exception: " + ex.Message);
         Assert.Contains("No connection is active/available to service this operation", ex.Message);
@@ -29,7 +29,7 @@ public async Task NeverEverConnectedNoBacklogThrowsConnectionNotAvailableAsync()
         var db = conn.GetDatabase();
         var key = Me();
 
-        // No connection is active/available to service this operation: GET 6.0.14AbortOnConnectFailTests-NeverEverConnectedThrowsConnectionNotAvailable; UnableToConnect on doesnot.exist.0d034c26350e4ee199d6c5f385a073f7:6379/Interactive, Initializing/NotStarted, last: NONE, origin: BeginConnectAsync, outstanding: 0, last-read: 0s ago, last-write: 0s ago, keep-alive: 500s, state: Connecting, mgr: 10 of 10 available, last-heartbeat: never, global: 0s ago, v: 2.6.99.22667, mc: 1/1/0, mgr: 10 of 10 available, clientName: NAMISTOU-3(SE.Redis-v2.6.99.22667), IOCP: (Busy=0,Free=1000,Min=32,Max=1000), WORKER: (Busy=2,Free=32765,Min=32,Max=32767), POOL: (Threads=17,QueuedItems=0,CompletedItems=20), v: 2.6.99.22667
+        // No connection is active/available to service this operation: GET 6.0.18AbortOnConnectFailTests-NeverEverConnectedNoBacklogThrowsConnectionNotAvailableSync; UnableToConnect on doesnot.exist.d4d1424806204b68b047954b1db3411d:6379/Interactive, Initializing/NotStarted, last: NONE, origin: BeginConnectAsync, outstanding: 0, last-read: 0s ago, last-write: 0s ago, keep-alive: 100s, state: Connecting, mgr: 4 of 10 available, last-heartbeat: never, global: 0s ago, v: 2.6.120.51136, mc: 1/1/0, mgr: 5 of 10 available, clientName: CRAVERTOP7(SE.Redis-v2.6.120.51136), IOCP: (Busy=0,Free=1000,Min=16,Max=1000), WORKER: (Busy=3,Free=32764,Min=16,Max=32767), POOL: (Threads=25,QueuedItems=0,CompletedItems=1066,Timers=46), v: 2.6.120.51136
         var ex = await Assert.ThrowsAsync<RedisConnectionException>(() => db.StringGetAsync(key));
         Log("Exception: " + ex.Message);
         Assert.Contains("No connection is active/available to service this operation", ex.Message);
@@ -49,7 +49,7 @@ public void DisconnectAndReconnectThrowsConnectionExceptionSync()
         var server = conn.GetServerSnapshot()[0];
         server.SimulateConnectionFailure(SimulatedFailureType.All);
 
-        // Exception: The message timed out in the backlog attempting to send because no connection became available (100ms) - Last Connection Exception: InternalFailure on 127.0.0.1:6379/Interactive, Initializing/NotStarted, last: GET, origin: ConnectedAsync, outstanding: 0, last-read: 0s ago, last-write: 0s ago, keep-alive: 500s, state: Connecting, mgr: 10 of 10 available, last-heartbeat: never, last-mbeat: 0s ago, global: 0s ago, v: 2.6.99.22667, command=PING, inst: 0, qu: 0, qs: 0, aw: False, bw: CheckingForTimeout, last-in: 0, cur-in: 0, sync-ops: 1, async-ops: 1, serverEndpoint: 127.0.0.1:6379, conn-sec: n/a, aoc: 0, mc: 1/1/0, mgr: 10 of 10 available, clientName: NAMISTOU-3(SE.Redis-v2.6.99.22667), IOCP: (Busy=0,Free=1000,Min=32,Max=1000), WORKER: (Busy=2,Free=32765,Min=32,Max=32767), POOL: (Threads=18,QueuedItems=0,CompletedItems=65), v: 2.6.99.22667 (Please take a look at this article for some common client-side issues that can cause timeouts: https://stackexchange.github.io/StackExchange.Redis/Timeouts)
+        // Exception: The message timed out in the backlog attempting to send because no connection became available (100ms) - Last Connection Exception: SocketFailure (InputReaderCompleted, last-recv: 7) on 127.0.0.1:6379/Interactive, Idle/ReadAsync, last: PING, origin: SimulateConnectionFailure, outstanding: 0, last-read: 0s ago, last-write: 0s ago, keep-alive: 100s, state: ConnectedEstablished, mgr: 10 of 10 available, in: 0, in-pipe: 0, out-pipe: 0, last-heartbeat: never, last-mbeat: 0s ago, global: 0s ago, v: 2.6.120.51136, command=PING, timeout: 100, inst: 13, qu: 1, qs: 0, aw: False, bw: Inactive, last-in: 0, cur-in: 0, sync-ops: 2, async-ops: 0, serverEndpoint: 127.0.0.1:6379, conn-sec: n/a, aoc: 0, mc: 1/1/0, mgr: 10 of 10 available, clientName: CRAVERTOP7(SE.Redis-v2.6.120.51136), IOCP: (Busy=0,Free=1000,Min=16,Max=1000), WORKER: (Busy=2,Free=32765,Min=16,Max=32767), POOL: (Threads=33,QueuedItems=0,CompletedItems=6237,Timers=39), v: 2.6.120.51136 (Please take a look at this article for some common client-side issues that can cause timeouts: https://stackexchange.github.io/StackExchange.Redis/Timeouts)
         var ex = Assert.ThrowsAny<Exception>(() => db.Ping());
         Log("Exception: " + ex.Message);
         Assert.True(ex is RedisConnectionException or RedisTimeoutException);
@@ -73,7 +73,7 @@ public async Task DisconnectAndNoReconnectThrowsConnectionExceptionAsync()
         var server = conn.GetServerSnapshot()[0];
         server.SimulateConnectionFailure(SimulatedFailureType.All);
 
-        // Exception: The message timed out in the backlog attempting to send because no connection became available (100ms) - Last Connection Exception: InternalFailure on 127.0.0.1:6379/Interactive, Initializing/NotStarted, last: GET, origin: ConnectedAsync, outstanding: 0, last-read: 0s ago, last-write: 0s ago, keep-alive: 500s, state: Connecting, mgr: 10 of 10 available, last-heartbeat: never, last-mbeat: 0s ago, global: 0s ago, v: 2.6.99.22667, command=PING, inst: 0, qu: 0, qs: 0, aw: False, bw: CheckingForTimeout, last-in: 0, cur-in: 0, sync-ops: 1, async-ops: 1, serverEndpoint: 127.0.0.1:6379, conn-sec: n/a, aoc: 0, mc: 1/1/0, mgr: 10 of 10 available, clientName: NAMISTOU-3(SE.Redis-v2.6.99.22667), IOCP: (Busy=0,Free=1000,Min=32,Max=1000), WORKER: (Busy=2,Free=32765,Min=32,Max=32767), POOL: (Threads=18,QueuedItems=0,CompletedItems=65), v: 2.6.99.22667 (Please take a look at this article for some common client-side issues that can cause timeouts: https://stackexchange.github.io/StackExchange.Redis/Timeouts)
+        // Exception: The message timed out in the backlog attempting to send because no connection became available (100ms) - Last Connection Exception: SocketFailure (InputReaderCompleted, last-recv: 7) on 127.0.0.1:6379/Interactive, Idle/ReadAsync, last: PING, origin: SimulateConnectionFailure, outstanding: 0, last-read: 0s ago, last-write: 0s ago, keep-alive: 100s, state: ConnectedEstablished, mgr: 8 of 10 available, in: 0, in-pipe: 0, out-pipe: 0, last-heartbeat: never, last-mbeat: 0s ago, global: 0s ago, v: 2.6.120.51136, command=PING, timeout: 100, inst: 0, qu: 0, qs: 0, aw: False, bw: CheckingForTimeout, last-in: 0, cur-in: 0, sync-ops: 1, async-ops: 1, serverEndpoint: 127.0.0.1:6379, conn-sec: n/a, aoc: 0, mc: 1/1/0, mgr: 8 of 10 available, clientName: CRAVERTOP7(SE.Redis-v2.6.120.51136), IOCP: (Busy=0,Free=1000,Min=16,Max=1000), WORKER: (Busy=6,Free=32761,Min=16,Max=32767), POOL: (Threads=33,QueuedItems=0,CompletedItems=5547,Timers=60), v: 2.6.120.51136 (Please take a look at this article for some common client-side issues that can cause timeouts: https://stackexchange.github.io/StackExchange.Redis/Timeouts)
         var ex = await Assert.ThrowsAsync<RedisConnectionException>(() => db.PingAsync());
         Log("Exception: " + ex.Message);
         Assert.StartsWith("The message timed out in the backlog attempting to send because no connection became available (100ms) - Last Connection Exception: ", ex.Message);

tests/StackExchange.Redis.Tests/ExceptionFactoryTests.cs

@@ -126,7 +126,12 @@ public void TimeoutException()
             Assert.Contains("conn-sec: n/a", ex.Message);
             Assert.Contains("aoc: 1", ex.Message);
 #if NETCOREAPP
-                Assert.Contains("POOL: ", ex.Message);
+            // ...POOL: (Threads=33,QueuedItems=0,CompletedItems=5547,Timers=60)...
+            Assert.Contains("POOL: ", ex.Message);
+            Assert.Contains("Threads=", ex.Message);
+            Assert.Contains("QueuedItems=", ex.Message);
+            Assert.Contains("CompletedItems=", ex.Message);
+            Assert.Contains("Timers=", ex.Message);
 #endif
             Assert.DoesNotContain("Unspecified/", ex.Message);
             Assert.EndsWith(" (Please take a look at this article for some common client-side issues that can cause timeouts: https://stackexchange.github.io/StackExchange.Redis/Timeouts)", ex.Message);