Spawn processing threads and enable enqueuing.
Declared in <bdlmt_fixedthreadpool.h>
int
start();
Spawn threads until there are numThreads() processing threads. On success, enable enqueuing and return 0. Otherwise, join all threads (ensuring false == isStarted()) and return -1. If the thread pool was already started (isStarted() is true), this method has no effect.
0 on success, and -1 otherwise