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Top Forums Shell Programming and Scripting Implementing Queue Using Shell scripts Post 302418547 by Corona688 on Tuesday 4th of May 2010 04:31:24 PM
Old 05-04-2010
There's probably lots of ways. One at a time is easy; anything that only one process can succeed at can be used as a locking mechanism, like mkfifo. Each process runs 'mkfifo /tmp/myfifo', if it succeeds, it has control until it deletes the fifo. if it doesn't, sleep a second then retry. Simple but not the most efficient, and not precisely a queue.

Two at a time is harder. Shell script doesn't have good mechanisms for tracking multiple children simultaneously, not in a manner to tell your script which child just terminated. It'd be possible with an arrangements of fifos to communicate between child and controller, but not trivial, and prone to breaking down when processes terminate unexpectedly.

It'd be simple enough to do and control with a makefile, if you have make.
 

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MKFIFO(3)						     Linux Programmer's Manual							 MKFIFO(3)

NAME
mkfifo - make a FIFO special file (a named pipe) SYNOPSIS
#include <sys/types.h> #include <sys/stat.h> int mkfifo(const char *pathname, mode_t mode); DESCRIPTION
mkfifo makes a FIFO special file with name pathname. mode specifies the FIFO's permissions. It is modified by the process's umask in the usual way: the permissions of the created file are (mode & ~umask). A FIFO special file is similar to a pipe, except that it is created in a different way. Instead of being an anonymous communications chan- nel, a FIFO special file is entered into the file system by calling mkfifo. Once you have created a FIFO special file in this way, any process can open it for reading or writing, in the same way as an ordinary file. However, it has to be open at both ends simultaneously before you can proceed to do any input or output operations on it. Opening a FIFO for reading normally blocks until some other process opens the same FIFO for writing, and vice versa. See fifo(4) for non-blocking handling of FIFO special files. RETURN VALUE
The normal, successful return value from mkfifo is 0. In the case of an error, -1 is returned (in which case, errno is set appropriately). ERRORS
EACCES One of the directories in pathname did not allow search (execute) permission. EEXIST pathname already exists. ENAMETOOLONG Either the total length of pathname is greater than PATH_MAX, or an individual file name component has a length greater than NAME_MAX. In the GNU system, there is no imposed limit on overall file name length, but some file systems may place limits on the length of a component. ENOENT A directory component in pathname does not exist or is a dangling symbolic link. ENOSPC The directory or filesystem has no room for the new file. ENOTDIR A component used as a directory in pathname is not, in fact, a directory. EROFS pathname refers to a read-only filesystem. CONFORMING TO
POSIX.1 SEE ALSO
mkfifo(1), read(2), write(2), open(2), close(2), stat(2), umask(2), fifo(4) Linux 1.2.13 1995-09-03 MKFIFO(3)
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