mknod ("/ tmp / MYFIFO ", S_IFIFO | 0666,0);

In this example, the file / tmp / MYFIFO is the FIFO file to be created. Its access authority is 0666. Access permissions
can also be modified using umask:

final_umask = requested_permissions & ~ original_umask

A commonly used method of using system call umask () is to temporarily clear the value of
umask : umask (0);
mknod ("/ tmp / MYFIFO", S_IFIFO | 0666,0);

In addition, mknod () The third parameter in can only be used when creating a device file. It includes the
major and minor device numbers of the device file .
}
}






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Operation FIFO

I / O operation on FIFO and I on normal pipeline / O operations are basically the same, with one major difference. The system call open is used to physically open a pipe. In a half-duplex pipeline, this is unnecessary. Because the pipeline is in the system kernel, not in a physical file system. In our example, we will use the pipeline like a file stream, that is, use fopen () to open the pipeline and fclose () to close it.
Look at the following simple service program process:
#include <stdio.h>
#include <stdlib.h>
#include <sys / stat.h>
#include <unistd.h>
#include <linux / stat.h>
# defineFIFO_FILE "MYFIFO"

{
FILE * fp;
charreadbuf [80];
/ * CreatetheFIFOifitdoesnotexist * /
umask (0);
mknod (FIFO_FILE, S_IFIFO | 0666,0);
while (1)
{
fp = fopen (FIFO_FILE, "r");
fgets (readbuf , 80, fp);
printf ("Receivedstring:% s", readbuf);
fclose (fp);
return (0);
Because the FIFO pipeline has a blocking function by default, you can run this program in the background:
$ fifoserver &
Let's take a look at the following simple client program:
#include <stdio.h>
#include <stdlib.h>
#defineFIFO_FILE "MYFIFO"
intmain (int argc, char * argv [])
{
FILE * fp;
if (argc! = 2) {
printf ("USAGE: fifoclient [string]");
exit (1);
}
if ((fp = fopen (FIFO_FILE, "w")) == NULL) {
perror ("fopen");
exit (1);
}
fputs (argv [1], fp);
fclose (fp);
return (0);
}


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Blocking FIFO

Under normal circumstances, there will be blocking on the FIFO pipeline. In other words, if a FIFO pipe is opened for reading, it will block until other processes open the pipe to write information. This process is also reversed. If you don't need a blocking function, you can set the O_NONBLOCK flag in the system call open (), which will cancel the default blocking function.



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message queue

in SystemV versions of UNIX, aT & T introduced three new forms of IPC Features (message queue, semaphore, and shared memory). But the BSD version of UNIX uses sockets as the main form of IPC. The Linux system supports both versions.

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msgget ()

system call msgget ()
If you want to create a new message queue, or want to access an existing message queue, you can use the system call msgget ().

System call: msgget ();
Prototype: intmsgget (key_t key, int msgflg);
Return value: If successful, return message queue identifier
If it fails, return -1: errno = EACCESS (permission not allowed)
EEXIST (queue already exists , Cannot be created)
EIDRM (the queue flag is deleted)
ENOENT (the queue does not exist)
ENOMEM (the memory is not enough when creating the queue)
ENOSPC (the maximum queue limit is exceeded

) The first parameter in the system call msgget () is the keyword value (usually Returned by ftok ()). Then this keyword value will be compared with other keyword values ​​already in the system kernel. At this time, the opening and access operations are related to the content of the parameter msgflg.
IPC_CREAT Create this queue if it is not in the kernel.
IPC_EXCL, when used with IPC_CREAT, fails if the queue already exists.