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\" $FreeBSD: src/lib/libpthread/man/pthread_key_create.3,v 1.12 2002/09/16 19:29:28 mini Exp $
\"
Dd May 29, 2015
Dt PTHREAD_KEY_CREATE 3
Os
Sh NAME
Nm pthread_key_create ,
Nm pthread_key_delete
Nd thread-specific data
Sh LIBRARY
Lb libpthread
Sh SYNOPSIS
In pthread.h
Ft int
Fn pthread_key_create "pthread_key_t *key" "void (*destructor)(void *)"
Ft int
Fn pthread_key_delete "pthread_key_t key"
Sh DESCRIPTION
The
Fn pthread_key_create
function creates a thread-specific data key visible to all threads in the
process.
Key values are opaque objects used to locate thread-specific data.
The same key value may be used by different threads,
but 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
Dv NULL
is associated with the new key in all active threads.
Upon thread creation, the value
Dv 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
Pf non- Dv NULL
destructor pointer, and the thread has a
Pf non- Dv 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
Pf non- Dv NULL
values with associated destructors, there are still some
Pf non- Dv NULL
values with associated destructors, then the process is repeated.
If, after at least
Dv PTHREAD_DESTRUCTOR_ITERATIONS
iterations of destructor calls for outstanding
Pf non- Dv NULL
values, there are still some
Pf non- Dv NULL
values with
associated destructors, the implementation stops calling destructors.
Pp
The
Fn pthread_key_delete
function deletes a thread-specific data key previously returned by
Fn pthread_key_create .
The thread-specific data values associated with
Fa key
need not be
Dv NULL
at the time of the call.
It is the responsibility of the application to free any
application storage or perform any cleanup actions for data structures
related to the deleted key or associated thread-specific data in any threads;
this cleanup can be done either before or after
Fn pthread_key_delete
is called.
Any attempt to use
Fa key
following the call to
Fn pthread_key_delete
results in undefined behavior.
Pp
The
Fn pthread_key_delete
function itself is callable from within destructor functions,
but destructor functions are not invoked by the function.
Any destructor function that may have been associated with
Fa key
will no longer be called upon thread exit.
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.
Also
Fn pthread_key_delete
will return zero upon success.
Upon failure both functions return an error number to indicate the cause.
Sh ENVIRONMENT
Bl -tag -width PTHREAD_KEYS_MAX
It Ev PTHREAD_KEYS_MAX
Maximum per-process thread-specific data keys.
This cannot be set below
Dv _POSIX_THREAD_KEYS_MAX .
El
Sh ERRORS
The
Fn pthread_key_create
may 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
Dv PTHREAD_KEYS_MAX
would be exceeded.
It Bq Er ENOMEM
Insufficient memory exists to create the key.
El
Pp
The
Fn pthread_key_delete
function may fail if:
Bl -tag -width Er
It Bq Er EINVAL
The
Fa key
value is invalid.
El
Sh SEE ALSO
Xr pthread_getspecific 3
Sh STANDARDS
These functions conform to
St -p1003.1-2001 .
Sh BUGS
The current specifications are flawed and
do not permit a clean implementation without potential problems.
The current implementation in
Nx
addresses these problems by not supporting key reuse.

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