Shulou(Shulou.com)06/01 Report--

This article to share with you is about how to linuxthreads source code analysis ptfork.c, Xiaobian think quite practical, so share to everyone to learn, I hope you can read this article after harvest, not much to say, follow Xiaobian to see it.

ptfork.c implements the pthread_atfork function, which is described in pthread_atfork(3) - Linux manual page and in the pthread_atfork.man file in the source code.

/* The "atfork" stuff */

#include

#include

#include

#include "pthread.h"

#include "internals.h"

struct handler_list {

void (*handler)(void);

struct handler_list * next;

};

//Mutex variables used for mutex access lists

static pthread_mutex_t pthread_atfork_lock = PTHREAD_MUTEX_INITIALIZER;

//three linked lists

static struct handler_list * pthread_atfork_prepare = NULL;

static struct handler_list * pthread_atfork_parent = NULL;

static struct handler_list * pthread_atfork_child = NULL;

//Create a new handler_list node and insert it into the list

static void pthread_insert_list(struct handler_list ** list,

void (*handler)(void),

struct handler_list * newlist,

int at_end)

{

if (handler == NULL) return;

//insert to the end, then point directly to the tail node first

if (at_end) {

while(*list != NULL) list = &((*list)->next);

}

//Save data to new node

newlist->handler = handler;

// *list is the address of the first node

newlist->next = *list;

// * Change the contents of the list to a new node

*list = newlist;

}

struct handler_list_block {

struct handler_list prepare, parent, child;

};

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

void (*parent)(void),

void (*child)(void))

{

struct handler_list_block * block =

(struct handler_list_block *) malloc(sizeof(struct handler_list_block));

if (block == NULL) return ENOMEM;

pthread_mutex_lock(&pthread_atfork_lock);

/* "prepare" handlers are called in LIFO */

//Save three functions into a node, if this node is inserted into three handle_list queues respectively

pthread_insert_list(&pthread_atfork_prepare, prepare, &block->prepare, 0);

/* "parent" handlers are called in FIFO */

pthread_insert_list(&pthread_atfork_parent, parent, &block->parent, 1);

/* "child" handlers are called in FIFO */

pthread_insert_list(&pthread_atfork_child, child, &block->child, 1);

pthread_mutex_unlock(&pthread_atfork_lock);

return 0;

}

// handle_list Functions for each node in the linked list

static inline void pthread_call_handlers(struct handler_list * list)

{

for (/*nothing*/; list != NULL; list = list->next) (list->handler)();

}

extern int __fork(void);

// http://man7.org/linux/man-pages/man3/pthread_atfork.3.html

/*

Glibc defines the relationship between fork and__fork.

weak_alias (__fork, fork)

# define weak_alias(name, aliasname) _weak_alias (name, aliasname)

# define _weak_alias(name, aliasname) \

extern __typeof (name) aliasname __attribute__ ((weak, alias (#name)))

fork is a weak symbol and is an alias for__fork. That is, if fork is defined, it overrides fork in glibc.

This is to override glibc's fork and then perform some extra operations before calling glibc's__fork. This way, when the user executes fork,

The following fork function is executed, thus executing glibc's__fork

*/

int fork(void)

{

int pid;

struct handler_list * prepare, * child, * parent;

pthread_mutex_lock(&pthread_atfork_lock);

prepare = pthread_atfork_prepare;

child = pthread_atfork_child;

parent = pthread_atfork_parent;

pthread_mutex_unlock(&pthread_atfork_lock);

//list of functions called before fork

pthread_call_handlers(prepare);

pid = __fork();

//child process

if (pid == 0) {

__pthread_reset_main_thread();

__fresetlockfiles();

pthread_call_handlers(child);

} else {

//parent process

pthread_call_handlers(parent);

}

return pid;

}

The above is how to carry out linuxthreads source code analysis ptfork.c, Xiaobian believes that some knowledge points may be seen or used in our daily work. I hope you can learn more from this article. For more details, please follow the industry information channel.

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.