Standard C Library Functions thr_keycreate(3C)
NAME
thr_keycreate, thr_keycreate_once, thr_setspecific,
thr_getspecific - thread-specific data functions
SYNOPSIS
cc -mt [ flag... ] file... [ library... ]
#include
int thr_keycreate(thread_key_t *keyp,
void (*destructor)(void *));int thr_keycreate_once(thread_key_t *keyp,
void (*destructor)(void *));int thr_setspecific(thread_key_t key, void *value);
int thr_getspecific(thread_key_t key, void **valuep);
DESCRIPTION
Create Key In general, thread key creation allocates a key that locates data specific to each thread in the process. The key is global to all threads in the process, which allows each thread to bind a value to the key once the key has been created. The key independently maintains specific values foreach binding thread. The thr_keycreate() function allocates
a global key namespace, pointed to by keyp, that is visible to all threads in the process. Each thread is initially bound to a private element of this key, which allows accessto its thread-specific data.
Upon key creation, a new key is assigned the value NULL for all active threads. Additionally, upon thread creation, all previously created keys in the new thread are assigned the value NULL.Optionally, a destructor function destructor can be associ-
ated with each key. Upon thread exit, if a key has a non-
null destructor function and the thread has a non-null value
associated with that key, the destructor function is calledwith the current associated value. If more than one destruc-
tor exists for a thread when it exits, the order of destruc-
tor calls is unspecified.SunOS 5.11 Last change: 2 Nov 2007 1
Standard C Library Functions thr_keycreate(3C)
An exiting thread runs with all signals blocked. All threadtermination functions, including thread-specific data des-
tructor functions, are called with all signals blocked.The thr_keycreate_once() function is identical to the
thr_keycreate() function except that the key pointed to by
keyp must be statically initialized with the valueTHR_ONCE_KEY before calling thr_keycreate_once() and the key
will be created exactly once. This is equivalent to usingpthread_once() to call a onetime initialization function
that calls thr_keycreate() to create the data key.
Set Value Once a key has been created, each thread can bind a newvalue to the key using thr_setspecific(). The values are
unique to the binding thread and are individually main-
tained. These values continue for the life of the calling thread. Proper synchronization of key storage and access must be ensured by the caller. The value argument tothr_setspecific() is generally a pointer to a block of
dynamically allocated memory reserved by the calling threadfor its own use. See EXAMPLES below.
At thread exit, the destructor function, which is associated at time of creation, is called and it uses the specific key value as its sole argument. Get Valuethr_getspecific() stores the current value bound to key for
the calling thread into the location pointed to by valuep.RETURN VALUES
If successful, thr_keycreate(), thr_keycreate_once(),
thr_setspecific() and thr_getspecific() return 0. Otherwise,
an error number is returned to indicate the error.ERRORS
If the following conditions occur, thr_keycreate() and
thr_keycreate_once() return the corresponding error number:
EAGAIN The system lacked the necessary resources tocreate another thread-specific data key.
ENOMEM Insufficient memory exists to create the key.SunOS 5.11 Last change: 2 Nov 2007 2
Standard C Library Functions thr_keycreate(3C)
If the following conditions occur, thr_setspecific() returns
the corresponding error number: ENOMEM Insufficient memory exists to associate the value with the key.The thr_setspecific() function returns the corresponding
error number: EINVAL The key value is invalid.EXAMPLES
Example 1 Call the thread-specific data from more than one
thread without special initialization.In this example, the thread-specific data in this function
can be called from more than one thread without special ini-
tialization. For each argument passed to the executable, athread is created and privately bound to the string-value of
that argument./* cc -mt thisfile.c */
#include
#include
#include
#include
void *thread_specific_data(void *);
void cleanup(void*);#define MAX_ARGC 20
thread_t tid[MAX_ARGC];
int num_threads;
int main(int argc, char *argv[]) { int i;num_threads = argc - 1;
for (i = 0; i < num_threads; i++)
thr_create(NULL, 0, thread_specific_data, argv[i+1], 0, &tid[i]);
for (i = 0; i < num_threads; i++)
thr_join(tid[i], NULL, NULL);
return (0); } /* end main */ void *thread_specific_data(void *arg) {
SunOS 5.11 Last change: 2 Nov 2007 3
Standard C Library Functions thr_keycreate(3C)
static thread_key_t key = THR_ONCE_KEY;
char *private_data = arg;
void *tsd = NULL; void *data;thr_keycreate_once(&key, cleanup);
thr_getspecific(key, &tsd);
if (tsd == NULL) {data = malloc(strlen(private_data) + 1);
strcpy(data, private_data);
thr_setspecific(key, data);
thr_getspecific(key, &tsd);
}printf("tsd for %d = %s\n", thr_self(), (char *)tsd);
thr_getspecific(key, &tsd);
printf("tsd for %d remains %s\n", thr_self(), (char *)tsd);
return (NULL);} /* end thread_specific_data */
void cleanup(void *v) {/* application-specific clean-up function */
free(v); }ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Interface Stability | Committed ||_____________________________|_____________________________|
| MT-Level | MT-Safe |
|_____________________________|_____________________________|
SEE ALSO
pthread_once(3C), thr_exit(3C), attributes(5), standards(5)
WARNINGSThe thr_getspecific() and thr_setspecific() functions can
be called either explicitly or implicitly from a thread-
specific data destructor function. Calling thr_setspecific()
from a destructor can result in lost storage or infinite loops.SunOS 5.11 Last change: 2 Nov 2007 4