uthread_atfork.c \

.\"

.\" "THE BEER-WARE LICENSE" (Revision 42m):

.\" <mikko@dynas.se> wrote this file.  As long as you retain this notice you

.\" can do whatever you want with this stuff. If we meet some day, and you think

.\" this stuff is worth it, you can buy me a beer in return.  Mikko Työläjärvi

.\"

.\" $FreeBSD$

.\"

.Dd March 16, 2000

.Dt PTHREAD_ATFORK 3

.Os BSD 4

.Sh NAME

.Nm pthread_atfork

.Nd register fork handlers

.Sh SYNOPSIS

.Fd #include <pthread.h>

.Ft int

.Fn pthread_atfork "void (*prepare)(void)" "void (*parent)(void)" "void (*child)(void)"

.Sh DESCRIPTION

The

.Fn pthread_atfork

function registers fork handlers to be called before and after

.Fn fork .

Handlers are run in the context of the thread that calls

.Fn fork .

.Pp

The

.Fa prepare

handlers are invoked before fork processing. The

.Fa parent

and

.Fa child

handlers are invoked after fork processing, in the parent and child

processes respectively.

Handlers will be called in the parent process even when the

.Fn fork

operation fails.

.Pp

Any number of handlers can be registered by

.Fn pthread_atfork .

Function pointers that are NULL will be ignored.

The 

.Fa Parent

and

.Fa child

handlers are called in the order that they were registered. The

.Fn prepare

handlers are called in the reverse order.

.Pp

.Sh RETURN VALUES

If successful, the

.Fn pthread_atfork

function will return zero.

Otherwise an error number will be returned to

indicate the error.

.Sh ERRORS

.Fn pthread_atfork

will fail if:

.Bl -tag -width Er

.It Bq Er ENOMEM

The process cannot allocate enough memory to register another set of

handlers.

.El

.Pp

.Sh SEE ALSO

.Xr fork 2 ,

.Xr atexit 3

.Sh STANDARDS

.Fn pthread_atfork

conforms to ISO/IEC 9945-1 ANSI/IEEE

.Pq Dq Tn POSIX

.\" XXX: Dunno -- someone will have to check the exact details:

Std 1003.1 Second Edition 1996-07-12.

int		pthread_atfork __P((void (*prepare)(void),

				    void (*parent)(void), void (*child)(void)));

/* Atfork handlers */

#define ATFORK_PREPARE	0

#define ATFORK_PARENT	1

#define ATFORK_CHILD	2

typedef struct atfork_data {

	struct atfork_data *next, *prev;

	void (*funcs[3])(void);

} atfork_data;

atfork_data *_thread_atfork_list(void);

/*

 * "THE BEER-WARE LICENSE" (Revision 42m):

 * <mikko@dynas.se> wrote this file.  As long as you retain this notice you

 * can do whatever you want with this stuff. If we meet some day, and you think

 * this stuff is worth it, you can buy me a beer in return.  Mikko Työläjärvi

 *

 * $FreeBSD$

 */

#include <errno.h>

#include <stdlib.h>

#ifdef _THREAD_SAFE

#include <pthread.h>

#include "pthread_private.h"

static atfork_data *atfork_list = NULL;

static spinlock_t atfork_lock	= _SPINLOCK_INITIALIZER;

int

pthread_atfork(void (*prepare)(void),

	       void (*parent)(void),

	       void (*child)(void))

{

	atfork_data *ap;

	if (prepare == NULL && parent == NULL && child == NULL)

		return 0;

	if ((ap = malloc(sizeof(atfork_data))) == NULL)

		return ENOMEM;

	ap->funcs[ATFORK_PREPARE] = prepare;

	ap->funcs[ATFORK_PARENT] = parent;

	ap->funcs[ATFORK_CHILD] = child;

	_SPINLOCK(&atfork_lock);

	if ((ap->next = atfork_list) != NULL)

		atfork_list->prev = ap;

	atfork_list = ap;

	_SPINUNLOCK(&atfork_lock);

	return 0;

}

atfork_data *

_thread_atfork_list(void)

{

	atfork_data *ap;

	_SPINLOCK(&atfork_lock);

	ap = atfork_list;

	_SPINUNLOCK(&atfork_lock);

	return ap;

}

#endif

	atfork_data	*ap, *alist;

	/* Run any registered "prepare" callbacks: */

	alist = _thread_atfork_list();

	for (ap = alist; ap != NULL; ap = ap->next) {

		if (ap->funcs[ATFORK_PREPARE] != NULL)

			ap->funcs[ATFORK_PREPARE]();

		if (ap->next == NULL)

			break;

	}

	/*

	 * Run any parent/child callbacks matching the "prepare" callbacks

	 * from function entry, in reverse order:

	 */

	i = ret ? ATFORK_PARENT : ATFORK_CHILD;

	for (; ap != NULL; ap = (ap != alist) ? ap->prev : NULL)

		if (ap->funcs[i] != NULL)

			ap->funcs[i]();