Bug 29372 - BlockingCollection<T>.TakeFromAny causes 100% CPU load on Linux
Summary: BlockingCollection<T>.TakeFromAny causes 100% CPU load on Linux
Status: RESOLVED FIXED
Alias: None
Product: Class Libraries
Classification: Mono
Component: System ()
Version: 3.12.0
Hardware: PC Linux
: --- normal
Target Milestone: Untriaged
Assignee: Bugzilla
URL:
Depends on:
Blocks:
 
Reported: 2015-04-24 09:35 UTC by tobias.tretter
Modified: 2015-04-27 06:54 UTC (History)
3 users (show)

Tags:
Is this bug a regression?: ---
Last known good build:

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Status:
RESOLVED FIXED

Description tobias.tretter 2015-04-24 09:35:40 UTC
I have added a small test program to show the bug. If I use the BlockingCollection<T>.TakeFromAny call in the example, this causes 100% CPU load. It seems that it is busy waiting forever. The alternative, BlockingCollection<T>.TryTakeFromAny(..., out ..., Timeout.Infinite) however shows 0% CPU load. I would have expected same behavior. So it seems that there is a work around, but nevertheless, the bug should be fixed. I could not see any load problems using the .net version or mono on windows PC.

using System;
using System.Collections.Concurrent;
using System.Threading;
using System.Threading.Tasks;

namespace Hello
{
    class MainClass
    {
        static void Main(string[] args)
        {
            var low    = new BlockingCollection<int>(1);
            var high   = new BlockingCollection<int>(1);
            var array  = new BlockingCollection<int>[] { high, low };

            Task.Run(() => {
                int i = -1;
                while (true) {
                    try {
                        BlockingCollection<int>.TakeFromAny(array, out i);  // 100% CPU load
                        //BlockingCollection<int>.TryTakeFromAny(array, out i, Timeout.Infinite); // 0% CPU load
                    }
                    catch (InvalidOperationException) {
                        break;
                    }
                }
            });

            Task.Run(() => {
                for (int i = 0; ; i++) {
                    low.Add(i);
                    Thread.Sleep(500);
                }
            });

            Task.Run(() => {
                for (int i = 10000; ; i--) {
                    high.Add(i);
                    Thread.Sleep(500);
                }
            });

            Console.ReadLine();
        }
    }
}
Comment 1 Marek Safar 2015-04-27 06:54:38 UTC
Fixed in Mono 4.0