06-23-2008
Note: #include <unistd.h> needs to be added at the top of the file. Your compiler should complain, a lot. Do not run code with warnings or errors, even if ti compiles.
each fork call creates a child process, which then runs the code - whatever is left to to run. The parent of the child also keeps running from that point as well, so you have two (or more processes ) running the same code. On the console you will see one A, two B's, more C's and a lot more D's. They will not appear in the order you expect, because of the way the OS schedules processes access to the cpu. And the order may change from with each new run, depnding on the overall load on the system.
See if you can work out why.
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LEARN ABOUT OSX
pthread_atfork
PTHREAD_ATFORK(3) BSD Library Functions Manual PTHREAD_ATFORK(3)
NAME
pthread_atfork -- register handlers to be called before and after fork()
SYNOPSIS
#include <pthread.h>
int
pthread_atfork(void (*prepare)(void), void (*parent)(void), void (*child)(void));
DESCRIPTION
The pthread_atfork() function is used to register functions to be called before and after fork(). The prepare handler is called before
fork(), while the parent and child handlers are called after fork() in the parent and child process respectively. The prepare handlers are
called in reverse order of their registration, while parent and child handlers are called in the order in which they were registered. Any of
the handlers may be NULL.
Important: only async-signal-safe functions are allowed on the child side of fork(). See sigaction(2) for details.
RETURN VALUES
If successful, the pthread_atfork() function will return zero; otherwise an error number will be returned to indicate the error.
ERRORS
pthread_atfork() will fail if:
[ENOMEM] The system lacked the necessary resources to add another handler to the list.
SEE ALSO
fork(2)
STANDARDS
pthread_atfork() conforms to ISO/IEC 9945-1:1996 (``POSIX.1'').
BSD
August 12, 2004 BSD