Linux Study Notes (7)

Linux Study Notes (7)-Linux general technology-Linux programming and kernel information. The following is a detailed description. 11. elementary learning of Pipelines
MPs queue-special files, which are independent and only exist in memory
-- Process generated by the same process (Same Origin)
-- Half-duplex communication is adopted. Only one party can transmit data at a time.
Low-level MPs queue
Use the pipe function to create a low-level pipeline. After the pipeline is created, two file descriptors, pipe_fd [0] And pipe_fd [1], are generated. Pipe_fd [0] is used to read data from the pipeline, and pipe_fd [1] is used to write data to the pipeline (read and write functions are used to read and write data ).
Pipeline Data Flow Diagram
[Table = 98%] [tr] [td] MPs queue

[/Td] [/tr] [/table] [table = 98%] [tr] [td] fd [1]

[/Td] [/tr] [/table] [table = 98%] [tr] [td] fd [0]

[/Td] [/tr] [/table] [table = 98%] [tr] [td] Pipeline

[/Td] [/tr] [/table] [table = 98%] [tr] [td] fd [1]

[/Td] [/tr] [/table] [table = 98%] [tr] [td] fd [0]

[/Td] [/tr] [/table]
Common functions in pipeline operations

Pipe
Create an unknown MPs queue

Popen
Create a standard Stream pipeline

Mkfifo
Determine whether to detect or change the signal shielding word

Pipe Function Description
[Table] [tr] [td = 115,] function header file
[/Td] [td = 453,] # include
[/Td] [/tr] [tr] [td = 115,] function prototype
[/Td] [td = 1,1, 453] int
Pipe (int files [2])
[/Td] [/tr] [tr] [td = 115,] function return value
[/Td] [td = 453,] 0 is returned for successful execution, and-1 is returned for unsuccessful execution
[/Td] [/tr] [/table] programming: To design a program, you must create a pipeline, copy the process, write data to the parent process, and read data from the child process.

Flowchart


[Table = 98%] [tr] [td] creating an MPS queue

[/Td] [/tr] [/table] [table = 98%] [tr] [td]

[/Td] [/tr] [/table] [table = 98%] [tr] [td] fork () create a sub-process

[/Td] [/tr] [/table] [table= 98%] [tr] [td] if

[/Td] [/tr] [/table] [table = 98%] [tr] [td] disable fd [0]

[/Td] [/tr] [/table] [table = 98%] [tr] [td] write data to the pipeline

[/Td] [/tr] [/table] [table = 98%] [tr] [td] disable fd [1]

[/Td] [/tr] [/table] [table = 98%] [tr] [td] wait until the sub-process ends

[/Td] [/tr] [/table] [table = 98%] [tr] [td] Ends

[/Td] [/tr] [/table] [table = 98%] [tr] [td] disable fd [1]

[/Td] [/tr] [/table] [table = 98%] [tr] [td] read data from the pipeline

[/Td] [/tr] [/table] [table = 98%] [tr] [td] disable fd [0]

[/Td] [/tr] [/table] [table = 98%] [tr] [td] exit

[/Td] [/tr] [/table] 0 parent process "fitpath =" t "trim =" t ">


Result = fork ();
/* Creat subprocess */



If (result <0) {printf ("ERROR"); exit (0);}/* failture */

Else if (result = 0)

{Close (pipe_fd [1]);

If (r_num = read (pipe_fd [0], buf_r, 100)> 0)

Printf ("subprocess readed % d character from pipe, context is % s \ n", r_num, buf_r );

Close (pipe_fd [0]);

Exit (0 );

}


/* Father process */

Else

{

Close (pipe_fd [0]);

If (write (pipe_fd [1], "hello, world! ", 20 )! =-1)

Printf ("input string is 'hello, world' \ n ");



Close (pipe_fd [1]);

Waitpid (result, NULL, 0 );


Exit (0 );

}

}