I remember I typed "./client localhost & ./client localhost & ...." for repeating over 500+ times , in testing some network program.
And when I met some kind of stuck in the program, I got the error Resource temporarily unavailable, then can't start more client to test.
Even more, I can't even start a console terminator.
Here come the explanation :
"
Linux系统中每个线程都拥有独立的栈空间，而我的系统上调用ulimit -a看到的结果如下：
[dengwei@localhost ~]$ ulimit -a
core file size (blocks, -c) 0
data seg size (kbytes, -d) unlimited
scheduling priority (-e) 0
file size (blocks, -f) unlimited
pending signals (-i) 15916
max locked memory (kbytes, -l) 64
max memory size (kbytes, -m) unlimited
open files (-n) 1024
pipe size (512 bytes, -p) 8
POSIX message queues (bytes, -q) 819200
real-time priority (-r) 0
stack size (kbytes, -s) 8192
cpu time (seconds, -t) unlimited
max user processes (-u) 1024
virtual memory (kbytes, -v) unlimited
core file size (blocks, -c) 0
data seg size (kbytes, -d) unlimited
scheduling priority (-e) 0
file size (blocks, -f) unlimited
pending signals (-i) 15916
max locked memory (kbytes, -l) 64
max memory size (kbytes, -m) unlimited
open files (-n) 1024
pipe size (512 bytes, -p) 8
POSIX message queues (bytes, -q) 819200
real-time priority (-r) 0
stack size (kbytes, -s) 8192
cpu time (seconds, -t) unlimited
max user processes (-u) 1024
virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited
可以看到stack size是8M, 400个线程就需要8*400=3200M，虚拟内存不够用。
解决办法有两种：
1.使用ulimit -s 1024*1024命令，将线程栈大小临时设置成1M,经过试验能同时创建2000个线程了。
2.使用pthread_attr_setstacksize在程序中改变线程栈大小。
"