Add a timer test

src/System.Threading.Timer/tests/System.Threading.Timer.Tests.csproj

@@ -3,6 +3,7 @@
     <ProjectGuid>{ac20a28f-fda8-45e8-8728-058ead16e44c}</ProjectGuid>
     <Configurations>netcoreapp-Debug;netcoreapp-Release;netstandard-Debug;netstandard-Release</Configurations>
     <TestRuntime>true</TestRuntime>
+    <IncludeRemoteExecutor>true</IncludeRemoteExecutor>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="TimerConstructorTests.cs" />
@@ -12,4 +13,9 @@
   <ItemGroup Condition="'$(TargetGroup)' == 'netcoreapp'">
     <Compile Include="TimerDisposeTests.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <Compile Include="$(CommonTestPath)\System\Threading\ThreadTestHelpers.cs">
+      <Link>CommonTest\System\Threading\ThreadTestHelpers.cs</Link>
+    </Compile>
+  </ItemGroup>
 </Project>

src/System.Threading.Timer/tests/TimerFiringTests.cs

@@ -10,6 +10,7 @@
 using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
+using System.Threading.Tests;
 using Xunit;
 using Xunit.Sdk;
 
@@ -337,4 +338,57 @@ private static async Task PeriodAsync(int period, int iterations)
             await tcs.Task.ConfigureAwait(false);
         }
     }
+
+    [Fact]
+    public void TimersCreatedConcurrentlyOnDifferentThreadsAllFire()
+    {
+        int processorCount = Environment.ProcessorCount;
+
+        int timerTickCount = 0;
+        TimerCallback timerCallback = _ => Interlocked.Increment(ref timerTickCount);
+
+        var threadStarted = new AutoResetEvent(false);
+        var createTimers = new ManualResetEvent(false);
+        var timers = new Timer[processorCount];
+        Action<object> createTimerThreadStart = data =>
+        {
+            int i = (int)data;
+            var sw = new Stopwatch();
+            threadStarted.Set();
+            createTimers.WaitOne();
+
+            // Use the CPU a bit around creating the timer to try to have some of these threads run concurrently
+            sw.Restart();
+            do
+            {
+                Thread.SpinWait(1000);
+            } while (sw.ElapsedMilliseconds < 10);
+
+            timers[i] = new Timer(timerCallback, null, 1, Timeout.Infinite);
+
+            // Use the CPU a bit around creating the timer to try to have some of these threads run concurrently
+            sw.Restart();
+            do
+            {
+                Thread.SpinWait(1000);
+            } while (sw.ElapsedMilliseconds < 10);
+        };
+
+        var waitsForThread = new Action[timers.Length];
+        for (int i = 0; i < timers.Length; ++i)
+        {
+            var t = ThreadTestHelpers.CreateGuardedThread(out waitsForThread[i], createTimerThreadStart);
+            t.IsBackground = true;
+            t.Start(i);
+            threadStarted.CheckedWait();
+        }
+
+        createTimers.Set();
+        ThreadTestHelpers.WaitForCondition(() => timerTickCount == timers.Length);
+
+        foreach (var waitForThread in waitsForThread)
+        {
+            waitForThread();
+        }
+    }
 }