.\" Copyright (c) 1996 John Birrell <jb@cimlogic.com.au>.
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.Dd April 4, 1996
.Dt PTHREAD_KEY_CREATE 3
.Os
.Sh NAME
.Nm pthread_key_create
.Nd thread-specific data key creation
.Sh SYNOPSIS
.Fd #include <pthread.h>
.Ft int
.Fn pthread_key_create "pthread_key_t *key" "void (*destructor)(void *)"
.Sh DESCRIPTION
The
.Fn pthread_key_create
function creates a thread-specific data key visible to all threads in the
process. Key values provided by
.Fn pthread_key_create
are opaque objects used to locate thread-specific data. Although the same
key value may be used by different threads, the values bound to the key
by
.Fn pthread_setspecific
are maintained on a per-thread basis and persist for the life of the calling
thread.
.Pp
Upon key creation, the value NULL is associated with the new key in all
active threads. Upon thread creation, the value NULL is associated with all
defined keys in the new thread.
.Pp
An optional destructor function may be associated with each key value. At
thread exit, if a key value has a non-NULL destructor pointer, and the
thread has a non-NULL value associated with the key, the function pointed
to is called with the current associated value as its sole argument. The
order of destructor calls is unspecified if more than one destructor exists
for a thread when it exits.
.Pp
If, after all the destructors have been called for all non-NULL values
with associated destructors, there are still some non-NULL values with
associated destructors, then the process is repeated. If, after at least
[PTHREAD_DESTRUCTOR_ITERATIONS] iterations of destructor calls for
outstanding non-NULL values, there are still some non-NULL values with
associated destructors, the implementation stops calling destructors.
.Sh RETURN VALUES
If successful, the
.Fn pthread_key_create
function will store the newly created key value at the location specified by
.Fa key
and returns zero. Otherwise an error number will be returned to indicate
the error.
.Sh ERRORS
.Fn pthread_key_create
will fail if:
.Bl -tag -width Er
.It Bq Er EAGAIN
The system lacked the necessary resources to create another thread-specific
data key, or the system-imposed limit on the total number of keys per process
[PTHREAD_KEYS_MAX] would be exceeded.
.It Bq Er ENOMEM
Insufficient memory exists to create the key.
.El
.Sh SEE ALSO
.Xr pthread_getspecific 3 ,
.Xr pthread_key_delete 3 ,
.Xr pthread_setspecific 3
.Sh STANDARDS
.Fn pthread_key_create
conforms to ISO/IEC 9945-1 ANSI/IEEE
.Pq Dq Tn POSIX
Std 1003.1 Second Edition 1996-07-12.