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Top Forums Programming IPC - pipes between parent and child process Post 302473541 by Loic Domaigne on Sunday 21st of November 2010 06:25:28 AM
Old 11-21-2010
Using for instance a pipe between the parent and the child (write end at the parent, read end at the child), you may synchronize as follows: the child waits (i.e. reads the pipe using a blocking read) until the parent tells the child to go ahead (by writing something into the pipe). You ensure that the child will only execute once the parent told to do so.

If you need to synchronize the other way around (parent waits - child tells), use a pipe in the other direction (write end at the child, read end at the parent). And if you need to synchronize in both directions, you will need two pipes.

HTH,
Loïc
 

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filter_create_fd(3)						   util/filter.h					       filter_create_fd(3)

NAME
filter_create_fd - Create a sub process and return the requested pipes SYNOPSIS
#include <util/filter.h> NEOERR *filter_create_fd(const char *cmd, int *fdin, int *fdout, int *fderr, pid_t *pid); ARGUMENTS
cmd -> the sub command to execute. Will be executed with /bin/sh -c fdin -> pointer to return the stdin pipe, or NULL if you don't want the stdin pipe fdout -> pointer to return the stdout pipe, or NULL if you don't want the stdout pipe fderr -> pointer to return the stderr pipe, or NULL if you don't want the stderr pipe DESCRIPTION
filter_create_fd and filter_create_fp are what popen been: a mechanism to create sub processes and have pipes to all their input/output. The concept was taken from mutt, though python has something similar with popen3/popen4. You control which pipes the function returns by the fdin/fdout/fderr arguments. A NULL value means "don't create a pipe", a pointer to an int will cause the pipes to be created and the value of the file descriptor stored in the int. You will have to close(2) the file descriptors yourself. RETURN VALUE
fdin -> the stdin file descriptor of the sub process fdout -> the stdout file descriptor of the sub process fderr -> the stderr file descriptor of the sub process pid -> the pid of the sub process SEE ALSO
filter_wait(3), filter_create_fp(3), filter_create_fd ClearSilver 12 July 2007 filter_create_fd(3)
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