OSF DCE Application Development Guide--Introduction and Style Guide

OSF DCE Application Development Guide—Introduction and Style Guide
2.3.2 Storage for Thread Specific Data
The pthread package provides the ability to allocate per-thread global storage using
per-thread data keys. That is, an application can create storage that has global scope
within a thread but which is private to each instance of that thread. To do this, the
application creates a global data key by calling pthread_keycreate( ). Each thread then
typically allocates storage of the required type and associates this instance with with the
global key by calling pthread_setspecific(). Routines that need to access the per-thread
storage do so by calling pthread_getspecific(), which returns the address of the thread’s
private instance.
The following code fragments show a sample model of per-thread-data key use:
/* Declare global data key storage */
pthread_key_t key;
main()
{
.
.
.
/* Create exactly one instance of the key. You could also use */
/* a pthread_once() routine... */
status = pthread_keycreate(&key, (pthread_destructor_t) destroy);
.
.
.
/* Start some threads... */
.
.
.
}
/* The following routines are called in each of the threads. */
/* They access the thread’s private instance of the "global" */
/* value. */
/* The following routine sets the value to a thread-specific */
/* value... */
void write_global(mytype value)
{
mytype *global_var;
global_var = (mytype*) malloc(sizeof(mytype));
pthread_setspecific(key, (pthread_addr_t)global_var);
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