Linux interprocess communication (IPC)
Description: First of all, I would like to write a few words to be asked in the interview at the time of the detailed1, why should there be interprocess communication? parsing: Because interprocess communication is mainly about exchanging data between different processes, and the exchange of data must be implemented by the kernel , the global variables of any process are invisible in another process, so the kernel opens up a buffer, Process a puts data into the kernel, and process B takes the data away from the kernel, enabling interprocess communication2. How many communication methods are there between interprocess communication? resolution: Pipe, FIFO, System V Message Queuing, System V Semaphore, System V shared memory3. How many kinds of communication are introduced? Parse: Pipe (pipe): Use pipe (int filedes[2]) to create the pipeline, the created pipeline has a read and write end, can only be used for the relationship between interprocess communication, one-way communication, byte-based throttling. FIFO (named pipe): overcomes the inter-pipeline communication between the relationships, it is to create a real file, and then write to the file, read to the file read data, always FIFO, with int mkfifo (const char *filename, mode_t mode), int mknod (const char *filename,mode_t mode | S_ififo, (dev_t) 0); The created pipeline can communicate with any interprocessThe most important three interprocess communication comes in: (1) System V Message Queuing: It is message-based Message Queuing, is also the creation of read and write terminals respectively, can be used for any interprocess communication, requires three functions to implement, int msgget (key_t key,int msgflg): Create a message queue or get an existing message queue, int msgrcv (int msgqid,void *msgp,size_t msgzs,long msgtype,int msgflg): Take a message from the queue, int msgsnd (int msgid, Const void*msgp,size_t Msgzs,int MSGFLG): Put data into message queue, int msgctl (int msgqid,int cmd,struct msgqid_ds *buf): Set Message Queuing properties(2) System V Semaphore: The semaphore itself does not have the ability to make data communication, it is equivalent to a lock, it is only an external resource identification, with the signal to achieve the process of mutual exclusion and synchronization, mainly by SEMGET,SEMOP,SEMCTL to achieve process communication, is equivalent to the P, v operation in the mutex(3) System V Shared Memory: Shared memory is the fastest communication in all IPC, because it creates a buffer in memory, all processes can be accessed by this buffer, it is fast mainly to access the data only two copies can be completed, While other inter-process communication requires four copies to complete the communication, it also has a fatal disadvantage in multi-process or multi-threaded thread security, all shared memory communication is generally with the semaphore or mutex, condition variable set used to ensure the data in the communication time consistencyPS:Message Queuing, semaphores, shared memory all have System V and POSIX points, there are some differences between them, the latter will be mended
Linux interprocess communication (IPC)
