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system_threading_monitor_lock_acquisition_scalability_improvement.md

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System.Threading.Monitor lock acquision scalability improvement

Scope

Transparent

Version Introduced

4.8

Source Analyzer Status

NotPlanned

Change Description

In applications running on .NET Framework 4.7.2 and earlier versions, when a thread, T, cannot acquire a lock, and other threads are also waiting to acquire it, thread T performs a spin-wait that may make it more difficult for other threads to acquire the lock. This behavior can cause a positive feedback loop that leads to a perpetual lock convoy.

Starting with applications running on the .NET Framework 4.8, a thread attempting to acquire a lock when there is a waiter present skips the portion of spin-waiting that makes it more difficult for other threads to acquire the lock.

  • Quirked
  • Build-time break

Recommended Action

For applications running on the .NET Framework 4.8, the spin-waiting behavior described above can be reverted to the behavior in .NET Framework 4.7.2 in one of the following ways:

By setting the following environment variable before starting the process: COMPlus_Monitor_SpinWithoutSleepWhenWaiterIsPresent=1

By including the runtime configuration option in .exe.config. Example:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <runtime>
    <Monitor_SpinWithoutSleepWhenWaiterIsPresent enabled="1"/>
  </runtime>
</configuration>

Affected APIs

  • M:System.Threading.Monitor.Enter(System.Object)
  • M:System.Threading.Monitor.Enter(System.Object,System.Boolean)
  • `M:System.Threading.Monitor.TryEnter(System.Object)
  • `M:System.Threading.Monitor.TryEnter(System.Object,System.Boolean@)
  • `M:System.Threading.Monitor.TryEnter(System.Object,System.Int32)
  • `M:System.Threading.Monitor.TryEnter(System.Object,System.Int32,System.Boolean@)
  • `M:System.Threading.Monitor.TryEnter(System.Object,System.TimeSpan)
  • `M:System.Threading.Monitor.TryEnter(System.Object,System.TimeSpan,System.Boolean@)