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/*
* tsd.c
*
* Description:
* POSIX thread functions which implement thread-specific data (TSD).
*/
/*
* Why we can't use Win32 TLS
* --------------------------
*
* In a word: Destructors
*
* POSIX 1003.1 1996, Section 17 allows for optional destructor functions
* to be associated with each key value.
*
* This is my (revised) understanding of how destructors work:
*
* A key is created by a single thread, which then provides in every
* existing thread a TSD matching the same key, but initialised
* to NULL. Each new thread will also get a matching key with value NULL.
* The creating thread can optionally associate a function, called a
* destructor, with the key.
*
* When each thread exits, it calls the destructor function, which
* will then perform an action on that threads key value
* only. (Previously I thought that only the key creating thread ran
* the destructor on the key in all threads. That proposition is
* sounding scarier by the minute.)
*
* SOME APPROACHES TO MANAGING TSD MEMORY
*
* We could simply allocate enough memory on process startup to hold
* all possible data for all possible threads.
*
* We could allocate memory for just a table to hold a single pointer
* for each of POSIX_THREAD_KEYS_MAX keys. pthread_key_create() could then
* allocate space for POSIX_THREADS_MAX key values in one hit and store
* the location of the array in the first table.
*
* The standard also suggests that each thread might store key/value pairs
* on its private stack. This seems like a good idea. I had concerns about
* memory leaks and key re-use if a key was deleted, but the standard talks
* at length on this and basically says it's up to the application to
* make sure everything goes smoothly here, making sure that proper cleanup
* is done before a key is deleted. (section B.17.1.3 in particular)
*
* One more thing to note: destructors must never be called on deleted keys.
*/
#include <errno.h>
#include "pthread.h"
#include "implement.h"
int
pthread_key_create(pthread_key_t *key, void (*destructor)(void *))
{
pthread_key_t k;
int ret = 0;
/* CRITICAL SECTION */
pthread_mutex_lock(&_pthread_tsd_mutex);
if (_pthread_tsd_key_next >= PTHREAD_KEYS_MAX)
ret = EAGAIN;
k = _pthread_tsd_key_next++;
_pthread_tsd_key_table[k].in_use = _PTHREAD_TSD_KEY_INUSE;
_pthread_tsd_key_table[k].destructor = destructor;
pthread_mutex_unlock(&_pthread_tsd_mutex);
/* END CRITICAL SECTION */
*key = k;
return ret;
}
int
pthread_setspecific(pthread_key_t key, void *value)
{
void ** keys;
int inuse;
/* CRITICAL SECTION */
pthread_mutex_lock(&_pthread_tsd_mutex);
inuse = (_pthread_tsd_key_table[key].in_use == _PTHREAD_TSD_KEY_INUSE);
pthread_mutex_unlock(&_pthread_tsd_mutex);
/* END CRITICAL SECTION */
if (! inuse)
return EINVAL;
keys = (void **) TlsGetValue(_pthread_TSD_keys_TlsIndex);
keys[key] = value;
return 0;
}
void *
pthread_getspecific(pthread_key_t key)
{
void ** keys;
int inuse;
/* CRITICAL SECTION */
pthread_mutex_lock(&_pthread_tsd_mutex);
inuse = (_pthread_tsd_key_table[key].in_use == _PTHREAD_TSD_KEY_INUSE);
pthread_mutex_unlock(&_pthread_tsd_mutex);
/* END CRITICAL SECTION */
if (! inuse)
return (void *) NULL;
keys = (void **) TlsGetValue(_pthread_TSD_keys_TlsIndex);
return keys[key];
}
int
pthread_key_delete(pthread_key_t key)
{
int ret = 0;
/* CRITICAL SECTION */
pthread_mutex_lock(&_pthread_tsd_mutex);
if (_pthread_tsd_key_table[key].in_use != _PTHREAD_TSD_KEY_INUSE)
{
ret = EINVAL;
}
else
{
_pthread_tsd_key_table[key].in_use = _PTHREAD_TSD_KEY_DELETED;
_pthread_tsd_key_table[key].destructor = NULL;
}
pthread_mutex_unlock(&_pthread_tsd_mutex);
/* END CRITICAL SECTION */
return ret;
}
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