Limiting factors of the number of concurrent threads

threads ulimit stack size

Source

• check ulimit -a
• PID number too big
  • check /proc/sys/kernel/threads-max
  • check /proc/sys/kernel/pid_max
  • check /sys/fs/cgroup/pids/user.slice/user-1000.slice/pids.max and /sys/fs/cgroup/pids/user.slice/user-1000.slice/pids.current while blocking occurs
• most likely: stack size is too big
  • 8 MiB by default
  • each thread gets assigned memory of this size
  • however, there cannot be more threads than the amount of total physical memory divided by these 8 MiB
  • decreasing the stack size automatically increases the number of possible concurrent threads
  • however: still check PID/threads settings above since these can now be a limiting factor