pthread.md

pthread

Threads

Sources:

• https://computing.llnl.gov/tutorials/pthreads/

POSIX threads.

Complex model with around 100 functions prefixed by pthread.

c11 and C++11 introduced a standard threading model, so in time this may become less important

Each thread has its own stack, but unlike process, global memory is shared.

Quicker to start than a process because less resource copy is needed.

In Linux they are based on the clone system call.

In GCC you must compile with -pthread.

Thread synchronization mechanisms

• mutexes - Mutual exclusion lock: Block access to variables by other threads. This enforces exclusive access by a thread to a variable or set of variables.

• joins - Make a thread wait till others are complete (terminated).

• condition variables - data type pthread_cond_t

Good tutorial: http://www.yolinux.com/TUTORIALS/LinuxTutorialPosixThreads.html#SYNCHRONIZATION

pthread_create

Create a new thread.

int pthread_create(
    pthread_t *restrict thread,
    const pthread_attr_t *restrict attr,
    void *(*start_routine)(void*),
    void *restrict arg
)

• thread

  Return value.

  Unique id of the created thread.

  Can be retrieved from the thread with pthread_self()

  In POSIX all threads of a process have the same PID. TODO confirm with reference

• attr: set thread attributes. NULL for defaults.

• start_routine: function that runs the thread code

  If this function does return x, it is the same as calling pthread_exit(x).

  This value can then be retrieve from pthread_join.

• arg: argument to start_routine, NULL if none.

pthread_join

Wait for a given thread to terminate.

If it has already terminated, does not wait.

pthread_self

Get thread id of current running thread.

Same value that is returned through the thread argument of pthread_create.

Vs Linux gettid: http://stackoverflow.com/questions/6372102/what-is-the-difference-between-pthread-self-and-gettid-which-one-should-i-u