CODEWITHSUNDEEP
clinuxpthreads
asio_guy
asio_guy

Reputation: 3767

pthread_create fails with EAGAIN

Consider this code snippet here, where I am trying to create a bunch of threads which end up processing a given task which simulates a race-condition.

const int thread_count = 128;
pthread_t threads[thread_count];

for (int n = 0; n != thread_count; ++n)
{
    ret = pthread_create(&threads[n], 0, test_thread_fun, &test_thread_args);
    if( ret != 0 )
    {
        fprintf( stdout, "Fail %d %d", ret, errno );
        exit(0);
     }
 }

Things generally works fine except occasionally pthread_create fails with errno EAGAIN "resource temporarily unavailable", I tried inducing usleep, and retry creating but with no real effect.

the failure is sporadic and on some boxes no failures and on some occurs very frequently.

any Idea what could be going wrong here ?

Edit - 1

update on max-threads 

cat /proc/sys/kernel/threads-max
256467

Edit 2

I think the inputs here kept me thinking, i'll probably do the below and post any results that are worth sharing.

  1. set stack size to a minimum value, I don't think thread_function uses any large arrays.
  2. increase my memory and swap ( and nullify any side effects )
  3. write a script to monitor the system behavior and see any other process/system daemon is interfering when this case is run, which is in turn can cause resource crunch.
  4. system hard and soft limits are pretty high so I'll leave them as they are at this point.

Upvotes: 13

Views: 33439

Answers (4)

user413990
user413990

Reputation: 49

There are not enough resources to start a new thread. Check if you have zombie threads on your system, or that you have enough memory etc on the system.

Upvotes: 1

R.. GitHub STOP HELPING ICE
R.. GitHub STOP HELPING ICE

Reputation: 215287

Check ulimit -a at your shell. You likely have a process limit set in login policy and Linux ridiculously also applies this to threads.

Upvotes: 0

Florian Weimer
Florian Weimer

Reputation: 33719

If your program makes sure that it never creates more threads than the system limit allows for (by joining threads before creating new ones), then you are likely running into this kernel bug:

With certain kinds of container technology, the race window appears to be much larger, and the bug is much easier to trigger. (This might depend on the types of cgroups in use.)

Upvotes: 1

madago
madago

Reputation: 149

You might have a system limit about the max number of thread per process. Try to see it with: cat /proc/sys/kernel/threads-max

Upvotes: 1

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