Save the "exited" threads in a "thread pool" and reuse them when new threads is needed, instead of creating and destroying threads again and again.

At the beginning, it was wriiten as a workaround for the memory leak of qemu-user when threads are created and destroyed.

Archived, because the bug has been fixed and merged to qemu 8.0.

DO NOT USE IN PRODUCTION ENVIRNOMENT

mkdir build
cd build
cmake ..
make

And then there should be a ./libthread_reuse.so.

LD_PRELOAD=path-to-libthread_reuse.so command

or if in qemu-user

qemu-ARCH -E LD_PRELOAD=path-to-libthread_reuse.so program

It hooks some functions of pthread:

• pthread_create: (origin) create a new thread; (hooked) if there isn't enough threads in the thread pool, then create a new one, else get a thread from pool and submit the task
• pthread_join: (origin) join the thread, after that the thread will be destroyed; (hooked) wait until the thread finish its task, and get the return value of the task function, and tell the real thread that it can come back to the pool
• pthread_detach: (origin) ...; (hooked) tell the thread that it can come back to the pool
• pthread_exit: (origin) exit the thread calling this function; (hooked) jump out of the task function via a long jump (exactly siglongjmp)
• pthread_kill: (origin) send a signal to the thread if the signal is not 0, or return whether the thread is terminated if the signal is 0; (hooked) send a signal if the signal is not 0, or return whether the task function is terminated if the signal is 0

• thread cancellation support
• handle more signals
• more comment and document
• code clean-up and better style
• more configurable
• more tests
• test suite
• better POSIX compatibility