LINUX study note 12-inter-process communication 1 Pipeline

1. Overview:
 
A) why inter-process communication: data transmission, resource sharing, notification events, and process control;
 
B) basic source:
 
1. UNIX Process Communication:
 
2. inter-process communication based on system v:
 
A) system v: a branch of the UNIX operating system interface
 
3. Posix inter-process communication:
 
A) Posix: port operating system interfaces
 
C) classification: pipelines; SIGNALS; message queues; shared memory; semaphores; sockets
 
2. Pipeline communication:
 
A) features:
 
1. One-way, first-in-first-out
 
2. Write: at the end of the MPs queue
 
3. Read: in the pipeline's header
 
B) Category:
 
1. Unknown pipeline: used for communication between parent and child Processes
 
2. Famous pipe: used for communication between any two processes
 
C) unknown pipeline:
 
1. Create a pipe: Int pipe (int filedis [2]);
 
A) Filedis [0]: used to read the media transcoding queue, file descriptor, and generate the media transcoding queue after the media transcoding queue is created.
 
B) Filedis [1]: used for writing Pipelines
 
C) Return Value: Success is 0, failure is-1
 
D) # include <unistd. h>
 
2. close the pipeline: close (filedis [0]); close (filedis [1]);
 
3. Note:
 
A) pipe () must be called before fork (). Otherwise, the sub-process will not inherit the file descriptor.
 
B) after creating a sub-process, you must disable unused ports.
 
C) in order to be able to read and write normally, the read process needs to wait for a while so that the write process can write data for a while.
 
4. write pipeline: write (filedis [1], "string", sizeof (s ));
 
5. read pipeline: read (filedes [0], buffer, 80 );
 
A) store the data in the buffer array. 80 is the length of the buffer.
 
D) famous pipelines:
 
1. essence: a file
 
2. Create a pipe: Int mkfifo (const char * pathname, mode_t mode );
 
A) If (mkfifo (pathname, O_CREAT | O_EXCL) <0) & (errno! = EEXIST ))
 
B) pathname: File Name
 
C) mode: File Permission. Once created, file programming is available.
 
D) Return Value: Success is 0, failure is-1
 
E) # include <sys/types. h>
 
# Include <sys/stat. h>
 
3. close the file: unlink (const char * pathname );
 
4. open the file: Int open (const char * pathname, int flags, [mode])
 
A) Fd = open (pathname, O_RDONLY | O_NONBLOCK)
 
B) Pathname: the complete path is required.
 
C) non-blocking MARK: O_NONBLOCK
 
1. Not used: the process will be blocked when the access fails to meet the requirements.
 
2. Use: When the access fails to meet the requirements, the process is not blocked and an error is returned immediately. errno is ENXIO.
 
5. write pipeline: write (fd, "string", sizeof (s ));
 
6. read pipeline: read (fd, buffer, 80 );
 
A) store the data in the buffer array. 80 is the length of the buffer.
 
B) Remember to clear the memset (buffer, 0, 80) in the buffer before each data read, # include <string. h>
 
C) Buffer should be in the string format
 
7. Note:
 
A) the data in the pipeline is read once.
 
B) the MPs queue is generally created and closed by the Data Reading Process.