Databases
StackOverflow2013
Postsdbo
POSlowdown on creating objects with many threads
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POSlowdown on creating objects with many threads
    primarykey
    data
    text
    <p>I'm doing a project that spawn some hundreds of threads. All these threads are in a "sleeping" condition (they are locked on a Monitor object). I have noticed that if I increase the number of "sleeping" threads the program slow down very much. The "funny" thing is that looking at the Task Manager it seems that the greater the number of threads, the more free is the processor. I have narrowed the problem to object creation. </p> <p>Can someone explain it to me? </p> <p>I have produced a small sample to test it. It's a console program. It creates a thread for each processor and measure it's speed with a simple test (a "new Object()" ). No, the "new Object()" isn't jitted away (try if you don't trust me). The main thread show the speed of each thread. Pressing CTRL-C, the program spawns 50 "sleeping" threads. The slow down begins with just 50 threads. With around 250 it's very visible on the Task Manager that the CPU isn't 100% used (on mine it's 82%). </p> <p>I have tried three methods of locking the "sleeping" thread: Thread.CurrentThread.Suspend() (bad, bad, I know :-) ), a lock on an already locked object and a Thread.Sleep(Timeout.Infinite). It's the same. If I comment the row with the new Object(), and I replace it with a Math.Sqrt (or with nothing) the problem isn't present. The speed doesn't change with the number of threads. Can someone else check it? Does anyone knows where is the bottle neck?</p> <p>Ah... you should test it in Release Mode WITHOUT launching it from the Visual Studio. I'm using XP sp3 on a dual processor (no HT). I have tested it with the .NET 3.5 and 4.0 (to test the different framework runtimes)</p> <pre><code>namespace TestSpeed { using System; using System.Collections.Generic; using System.Threading; class Program { private const long ticksInSec = 10000000; private const long ticksInMs = ticksInSec / 1000; private const int threadsTime = 50; private const int stackSizeBytes = 256 * 1024; private const int waitTimeMs = 1000; private static List&lt;int&gt; collects = new List&lt;int&gt;(); private static int[] objsCreated; static void Main(string[] args) { objsCreated = new int[Environment.ProcessorCount]; Monitor.Enter(objsCreated); for (int i = 0; i &lt; objsCreated.Length; i++) { new Thread(Worker).Start(i); } int[] oldCount = new int[objsCreated.Length]; DateTime last = DateTime.UtcNow; Console.Clear(); int numThreads = 0; Console.WriteLine("Press Ctrl-C to generate {0} sleeping threads, Ctrl-Break to end.", threadsTime); Console.CancelKeyPress += (sender, e) =&gt; { if (e.SpecialKey != ConsoleSpecialKey.ControlC) { return; } for (int i = 0; i &lt; threadsTime; i++) { new Thread(() =&gt; { /* The same for all the three "ways" to lock forever a thread */ //Thread.CurrentThread.Suspend(); //Thread.Sleep(Timeout.Infinite); lock (objsCreated) { } }, stackSizeBytes).Start(); Interlocked.Increment(ref numThreads); } e.Cancel = true; }; while (true) { Thread.Sleep(waitTimeMs); Console.SetCursorPosition(0, 1); DateTime now = DateTime.UtcNow; long ticks = (now - last).Ticks; Console.WriteLine("Slept for {0}ms", ticks / ticksInMs); Thread.MemoryBarrier(); for (int i = 0; i &lt; objsCreated.Length; i++) { int count = objsCreated[i]; Console.WriteLine("{0} [{1} Threads]: {2}/sec ", i, numThreads, ((long)(count - oldCount[i])) * ticksInSec / ticks); oldCount[i] = count; } Console.WriteLine(); CheckCollects(); last = now; } } private static void Worker(object obj) { int ix = (int)obj; while (true) { /* First and second are slowed by threads, third, fourth, fifth and "nothing" aren't*/ new Object(); //if (new Object().Equals(null)) return; //Math.Sqrt(objsCreated[ix]); //if (Math.Sqrt(objsCreated[ix]) &lt; 0) return; //Interlocked.Add(ref objsCreated[ix], 0); Interlocked.Increment(ref objsCreated[ix]); } } private static void CheckCollects() { int newMax = GC.MaxGeneration; while (newMax &gt; collects.Count) { collects.Add(0); } for (int i = 0; i &lt; collects.Count; i++) { int newCol = GC.CollectionCount(i); if (newCol != collects[i]) { collects[i] = newCol; Console.WriteLine("Collect gen {0}: {1}", i, newCol); } } } } } </code></pre>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USCharles
    1. USxanatos
    plurals
    1. This table or related slice is empty.
    1. PL
      singulars
      1. LTLinked
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POSlowdown on creating objects with many threads
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POSlowdown on creating objects with many threads
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. POSlowdown on creating objects with many threads
      1. This table or related slice is empty.
      1. VTUpMod
    1. COIf you're concerned about performance, you should not have many more than (cpucount) threads. Between (cpucount+2) and (cpucount*2) are good rules of thumb (and on your system, both come out to 4). Use queues of asynchronous I/O operations to keep the few threads busy instead of sleeping. The only time a thread should be waiting is when contended for a lock.
      singulars
      1. POSlowdown on creating objects with many threads
      1. USBen Voigt
    2. COI'm doing a "slow-motion" coroutines. The "switch time" between threads is irrelevant, so I can use threads (I have about a "switch"/second, so even if it loses some ms to make the switch between the old thread and the new thread I don't have any problem). There are always a number of threads running equal to the processor But if sleeping threads slow down everything, then I have a problem. No, I can't use the async library of MS, because it's "fake". It "rewrites" your program. I have to use some preexisting libraries.
      singulars
      1. POSlowdown on creating objects with many threads
      1. USxanatos
    3. COHave you considered using the TPL instead of explicitly creating threads? That way the framework can decide the most appropriate number of native threads to do the work.
      singulars
      1. POSlowdown on creating objects with many threads
      1. USRichard Szalay
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload