Thread local storage allows multi-threaded applications to have a separate instance of a given data item for each thread. Where a single-threaded application would use static or global data, this could lead to contention, dead lock or data corruption in a multi-threaded application. One example is the C errno variable, used for storing the erro code related to functions from the Standard C library. It is common practice (and required by POSIX) for compliers that support multi-threaded applications to provide a separate instance of errno for each thread, in order to avoid different thread competing to read or update the value.
related APIs in pthread.h.
int pthread_key_create(pthread_key_t *key, void (*destructor)(void *));
Returns 0 on success, or a positive error number on error
int pthread_key_delete(pthread_key_t key);
If successful, the pthread_key_delete() function shall return zero; otherwise, an error number shall be returned to indicate the error.
int pthread_setspecific(pthread_key_t key, const void *value);
Returns 0 on success, or a positive error number on error
void *pthread_getspecific(pthread_key_t key);
Returns pointer, or NULL if no thread-specific data isassociated with key
references:
Linux programming interface