Determine number of threads waiting in threadpool in C#

c#, multithreading

Solution

There is a ThreadPool.PendingWorkItemCount property.

https://learn.microsoft.com/en-us/dotnet/api/system.threading.threadpool.pendingworkitemcount?view=netcore-3.1

Another possibility if you're running .net core, is to run `dotnet counters monitor --process-id 123`

This will give you a console display of some runtime metrics. I believe the metric you're asking about is 3rd from the bottom.

Press p to pause, r to resume, q to quit.
    Status: Running

[System.Runtime]
    % Time in GC since last GC (%)                         0
    Allocation Rate / 1 sec (B)                       66,480
    CPU Usage (%)                                          0
    Exception Count / 1 sec                                0
    GC Heap Size (MB)                                    234
    Gen 0 GC Count / 60 sec                                0
    Gen 0 Size (B)                               200,991,744
    Gen 1 GC Count / 60 sec                                0
    Gen 1 Size (B)                                   385,440
    Gen 2 GC Count / 60 sec                                0
    Gen 2 Size (B)                               210,807,272
    LOH Size (B)                                  74,140,000
    Monitor Lock Contention Count / 1 sec                  0
    Number of Active Timers                              314
    Number of Assemblies Loaded                          272
    ThreadPool Completed Work Item Count / 1 sec          38
    ThreadPool Queue Length                                0
    ThreadPool Thread Count                                9
    Working Set (MB)                                     242

Some useful links:

https://learn.microsoft.com/en-us/dotnet/core/diagnostics/dotnet-counters https://www.youtube.com/watch?v=jn54CjePzs0

Problem

Is it possible to see how many threads are waiting to execute in the queue of the Threadpool? If I do this: ``` for (int i = 0; i < 5000; i++) { tasks.Add(Task.Run(() => { TaskTest(); })); } Task.WaitAll(tasks.ToArray()); ``` Inside TaskTest, I do some work that typically takes ~500ms, I also update a variable with the highest number of threads seen: ``` ThreadPool.GetMaxThreads(out maxthreads, out completionthreads); ThreadPool.GetAvailableThreads(out availablethreads, out completionthreads); int threads_in_use = maxthreads - availablethreads; mHighwaterThreads = Math.Max(mHighwaterThreads, threads_in_use); ``` Max threads, for my computer, is usually above 32000. mHighwaterThreads is usually around 75. I would like to know if there is a way to see how many threads are waiting to execute in the Threadpool.

Original source