Red Hat Bugzilla – Bug 43616
LD_ASSUME_KERNEL changes number of pthreads available.
Last modified: 2016-11-24 10:05:20 EST
Description of Problem: Without LD_ASSUME_KERNEL=2.2.5, the number of pthreads is limited to ~256, while with that symbol exported the available pthreads rises to ~1024, which is more consistent with other distributions/platforms. How Reproducible: 100% Steps to Reproduce: 1. Write a test program in {python|C|C++} that creates an infinite number of threads. It should print the number of threads after the first thread creation fails. 2. Run it without LD_ASSUME_KERNEL=2.2.5. 3. Run it again with that symbol defined. Actual Results: Out of the box, RHL 7.1 only supports ~256 threads on i686. Expected Results: Other platforms support many more threads. Additional Information: none
But, unlike when running with LD_ASSUME_KERNEL=2.2.5 (= non-LDT based threads, no floating thread stacks), this is no hard constant. It is as easy as ulimit -s 2048 to get the same thread limit as without LDT based threads, but one can even ulimit -s 256 and get loads of threads with smaller stacks. Of course, threads apps may call setrlimit before doing first pthread_create instead of relying on ulimit to be called in parent shell first.