The Solution--pthread_atfork(3T)

Use pthread_atfork() to prevent deadlocks whenever you use the fork one model.

#include <pthread.h>

int pthread_atfork(void (*prepare) (void), void (*parent) (void),
    void (*child) (void) );

The pthread_atfork() function declares fork() handlers that are called before and after fork() in the context of the thread that called fork().

• The prepare handler is called before fork() starts.

• The parent handler is called after fork() returns in the parent.

• The child handler is called after fork() returns in the child.

Any one of these can be set to NULL. The order in which successive calls to pthread_atfork() are made is significant.

For example, a prepare handler could acquire all the mutexes needed, and then the parent and child handlers could release them. This ensures that all the relevant locks are held by the thread that calls the fork function before the process is forked, preventing the deadlock in the child.

Using the fork all model avoids the deadlock problem described in "The Fork One Safety Problem and Solution".