[Reading Notes] pipelines and FIFO

MPs queue

Provides a single (one-way) data stream, which can provide communication means between two different processes.

#include <unistd.h>     pipe( fd[]);

Returns two file descriptors, fd [0] () and fd [1] ().

Communication between pipelines is usually completed using the read and write Functions.

 

Typical pipeline usage:

First, the parent process creates an pipeline and then calls fork to derive a copy of itself.

Next, the parent process closes the read end of the pipeline, and the child process closes the write segment of the pipeline.

In this way, a one-way data flow is provided between parent and child processes.

　

Dual-pipeline:

When a two-way data flow is required, we must create two pipelines, one in each direction.

    pipe1[], pipe2[( (childpid = Fork()) ==);

 

 

 

 

FIFO

It refers to the first in, first out, which is a one-way data stream.

Different from pipelines, each FIFO has a path name associated with it, which allows unrelated processes to access the same FIFO, and thus is also called "famous Pipeline ". ()

#include <sys/types.h><sys/stat.h> mkfifo( * pathname, mode_t mode);

Pathname is a path name and also the name of the FIFO.

Mode indicates the File Permission bit.

S_IRUSR S_IWUSR	User (owner) read User (owner) Write
S_IRGRP S_IWGRP	(Owner) group member read (Owner) group member write
S_IROTH S_IWOTH	Read by other members Write by other members

The constant value oo_mode is defined in unpipc. h:

 FIFE_MODE ( S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH )

 

Unlike pipelines:

　　　　

 FIFO1 "/tmp/fifo.1" FIFO2 "/tmp/fifo.2"( (mkfifo(FIFO1, FILE_MODE) < ) && (errno !=( (mkfifo(FIFO2, FILE_MODE) < ) && (errno !=( (childpid = Fork()) === Open(FIFO1, O_RDONLY, = Open(FIFO2, O_WRONLY,     = Open(FIFO1, O_WRONLY, = Open(FIFO2, O_RDONLY, );