Famous pipe piping Programming __ Programming

There are many ways to communicate between Linux processes and processes. The main ways to communicate between Linux processes are:

1, Nameless pipe

2. Famous pipe

3, Signal

4, Message Queuing

5. Shared Memory

6, Signal volume

7, Socket

Pipeline operations are simpler means of communication, one process writes data to the pipeline, and another process reads data from the pipeline. Pipelines include nameless pipes and well-known pipes. The former can be used only for communication between parent processes and child processes, which can be used between any two processes.

A well-known pipeline is also called a FIFO file, a well-known pipeline once created, Linux creates a file, reads and writes to the file, and communicates data between processes.

There are some differences between FIFO files and plain files:

1, read the FIFO file process can only be opened in a rdonly way

2, the process of writing FIFO files can only be opened in a wronly way

3, FIFO files inside the content is read, it disappeared, but the contents of ordinary files will not be read after the disappearance of

For a well-known pipe learning, or using a function, but the focus is two functions, one is to create a pipeline, one is to delete the pipeline. Because the pipe is the corresponding file, the operation of the pipe is the operation of the file, and the method used is consistent with the method of the file operation.

5.2 Creating a well-known pipeline

5.2.1 Name of the letter

Mkfifo

5.2.2 Function prototype

int Mkfifo (const char *pathname, mode_t mode)

5.2.3 Function Function

Create a well-known pipeline (FIFO file)

5.2.4 owned header file

<sys/types.h> <sys/stat.h>

5.2.5 return value

success: The file descriptor for the FIFO file

failure:-1

5.2.6 Parameter Description

Pathname: FIFO file name to create (with path)

mode: Permissions for the file created

0777:rwxrwxrwx

0666:rw-rw-rw-

5.3 Delete a named pipe

5.3.1 Name of the letter

unlink

5.3.2 Function prototype

int unlink (const char *pathname)

5.3.3 function Function

Delete files (including FIFO files)

5.3.4 owned header file

<unistd.h>

5.3.5 return value

Success: 0

failed: -1

5.3.6 Parameter Description

Pathname: FIFO file name to delete (with path)

Below, you need to write code to learn famous pipeline programming.

Write two programs, one program is responsible for creating a well-known pipeline, and to write data to a well-known pipeline, another program is responsible for reading well-known pipe data, and delete a well-known pipeline.

Corresponds to the Write process:

Running programs

As you can see, the program is blocked because the program is waiting for other processes to read the FIFO file contents. In the directory more than one fifo.txt file, this is the creation of the FIFO file. Look at this file and there's data written in it.

For read processes:

To run the program:

The write process ends because a process reads data from a FIFO file and the write process is no longer blocked. Read the process read FIFO file data successfully.

The following changes to read the process code, after reading the data, do not delete the FIFO file.

To run the program:

found that the FIFO file was not deleted. But in the file, there is no content, because it was read away.