vichargrave / wqueue Goto Github PK

Hi Vic, first of all thanks for sharing your code! It was just the missing peace to solve issues in my project!

Unfortunatly your code does not safely destroy the mutex. The documentation says:

It shall be safe to destroy an initialized mutex that is unlocked. Attempting to destroy a locked mutex, or a mutex that another thread is attempting to lock, or a mutex that is being used in a pthread_cond_timedwait() or pthread_cond_wait() call by another thread, results in undefined behavior.

Thats exactly what happens sometimes ;(

In my case ~wqueue() gets called from another thread while your wqueue::remove() method just executes pthread_cond_wait. However, pthread_mutex_destroy(&m_mutex) should never get called at this time. pthread_cond_wait checks at the beginning for destroyed mutex. That's why it doesn't always crash, but sometimes the destroy happens after that check ;(

To reproduce I open and immediately close the dialog that initializes and destroys the thread very often.

To safely destroy the thread probably requires a design change.

In Java I solved that problem with a work item that stops the thread. Maybe that would not require a vast design change.

I try to test it but there is a compile error like:
g++ -c -Wall -I../threads main.cpp -o main.o
g++ -c -Wall -I../threads ../threads/thread.cpp -o ../threads/thread.o
g++ -lpthread main.o ../threads/thread.o -o wqueue
../threads/thread.o: In function Thread::~Thread()': thread.cpp:(.text+0x9b): undefined reference to pthread_detach'
thread.cpp:(.text+0xb7): undefined reference to pthread_cancel' ../threads/thread.o: In function Thread::start()':
thread.cpp:(.text+0x11e): undefined reference to pthread_create' ../threads/thread.o: In function Thread::join()':
thread.cpp:(.text+0x16c): undefined reference to pthread_join' ../threads/thread.o: In function Thread::detach()':
thread.cpp:(.text+0x1c0): undefined reference to `pthread_detach'
collect2: error: ld returned 1 exit status
Makefile:12: recipe for target 'wqueue' failed
make: *** [wqueue] Error 1

Moreover, I want to get results back to the main().
How can I do it?
Best thanks for you help.