Multi-Thread task hangs up.

[zekungao]

Some testcase while repeating the STA calculations, met a problem that the multi-thread task hangs up.
The procedure didn't crash and can be terminated immediately.

The pstack show the final mirror is as:

Thread 1 (process 60192):
#0  0x00007f3c01a6071b in ?? ()
#1  0x0000556e3a7aae65 in sta::DispatchQueue::finishTasks() ()
...

We guess the mutex lock in multi-thread pool has some problem.

[zekungao]

The hack way to avoid this problem is to use following cmd to forced it to use only 1 thread

set_thread_count 1

But it may makes the STA calculation slower.