Pthread Functions

The pthread_mutex_init() routine creates a single mutual exclusion lock (mutex). EWL will always pass NULL as the second attr argument, which means to use default mutex attributes. Return zero upon success, return an error code upon failure.

The pthread_mutex_destroy() routine disposes of a single mutex. Return zero upon success, return an error code upon failure.

The pthread_mutex_lock() routine acquires a lock on a single mutex. If the mutex is already locked when pthread_mutex_lock() is called, the routine blocks execution of the current thread until the mutex is available. Return zero upon success, return an error code upon failure.

The pthread_mutex_unlock() routine releases a lock on a single mutex. Return zero upon success, return an error code upon failure.

Additionally, when EWL_LOCALDATA_AVAILABLE is on, four more pthread routines in the pthread_platform.c file are used by EWL to implement thread local data:

The pthread_key_create() routine creates a new thread local data identifier. Each thread can then access its own individual data elements through the identifier. When a thread terminates, the destructor routine is called with the single argument of pthread_getspecific() to clean up any necessary thread local data. Return zero upon success, return an error code upon failure.
The pthread_key_delete() routine disposes of a thread local data identifier. Return zero upon success, return an error code upon failure.
The pthread_setspecific() routine associates a value to a previously created thread local data identifier. The value is specific to the currently executing thread. Return zero upon success, return an error code upon failure.
The pthread_getspecific() routine retrieves a value associated with a thread local data identifier. The value is specific to the currently executing thread. If no value has been associated with the thread local data identifier, return NULL. Otherwise, return the previously associated value.

The following macros, listed in table below are used to configure and use the EWL threading support:

Table 1. EWL Thread Management Macros
Macro	Behavior
`EWL_THREADSAFE`	Defined to 0 if there is no multithread support in EWL. Defined to 1 if there should be multithread support in EWL. When defined to 1, many internal aspects of EWL are guarded by critical regions. Having critical regions inside EWL will slow down the execution time for the tradeoff of working correctly on a multithreaded system. Also, many EWL functions will use thread local storage for maintaining state information.
`EWL_PTHREADS`	Defined to 1 if the EWL platform supportsthe POSIX threading model. Defined to 0 if the EWL platform does not support the POSIX threading model. It is an error to define `EWL_PTHREADS` to 1 and `EWL_THREADSAFE` to 0. EWL has generic support for the POSIX thread model, so turning on `EWL_THREADSAFE` and `EWL_THREADS` is enough to properly support a multithreaded system without the need to write any additional support code.
`EWL_LOCALDATA`	Internal EWL flag for accessing thread local data when `EWL_THREADSAFE` is 1. Accesses static global data when `EWL_THREADSAFE`is 0.
`EWL_LOCALDATA_AVAILABLE`	Defined to 1 if the EWL platform supports thread local data, accessible using the `EWL_LOCALDATA` macro. Defined to 0 if the EWL platform does not support thread local data.