THE OPERATING SYSTEM MACHINE LEVEL - Structured Computer Organization - page 506

Thread call Meaning

pthread create Create a new thread in the called's address space

pthread exit Terminate the calling thread

pthread join Wait for a thread to terminate

pthread mutex init Create a new mutex

pthread mutex destroy Destroy a mutex

pthread mutex lock Lock a mutex

pthread mutex unlock Unlock a mutex

pthread cond init Create a condition variable

pthread cond destroy Destroy a condition variable

pthread cond wait Wait on a condition variable

pthread cond signal Release one thread waiting on a condition variable

Figure 6-44. The principal POSIX thread calls.

Mutexes can be created and destroyed by the calls pthread mutex init and
pthread mutex destroy , respectively. A mutex can be in one of two states: locked
or unlocked. When a thread needs to set a lock on an unlocked mutex (using
pthread mutex lock ), the lock is set and the thread continues. However, when a
thread tries to lock a mutex that is already locked, it blocks. When the locking
thread is finished with the shared resource, it is expected to unlock the correspond-
ing mutex by calling pthread mutex unlock .
Mutexes are intended for short-term locking, such as protecting a shared vari-
able. They are not intended for long-term synchronization, such as waiting for a
tape drive to become free. For long-term synchronization, condition variables are
provided. These are created and destroyed by calls to pthread cond init and
pthread cond destroy , respectively.
A condition variable is used by having one thread wait on it, and another signal
it. For example, having discovered that the tape drive it needs is busy, a thread
would do pthread cond wait on a condition variable that all the threads have
agreed to associate with the tape drive. When the thread using the tape drive is
finally done with it (possibly hours later), it uses pthread cond signal to release
exactly one thread waiting on that condition variable (if any). If no thread is wait-
ing, the signal is lost. Condition variables do not count like semaphores. A few
other operations are also defined on threads, mutexes, and condition variables.

Windows 7 Process Management

Windows 7 supports multiple processes, which can communicate and synchro-
nize. Each process contains at least one thread. Together, processes and threads
(which can be scheduled by the process itself) provide a general set of tools for