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This article mainly explains "how to achieve shared memory synchronization in Linux". Interested friends may wish to take a look. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn "how to synchronize shared memory with Linux".

Method 1. Using POSIX named semaphore to realize the synchronization of shared memory can be used not only for synchronization between threads, but also for synchronization between processes.

Two processes, reading and writing to the same shared memory, can use named semaphores to synchronize. One process writes, the other reads, using two named semaphores semr and semw. Semr semaphore controls whether it can be read or not, initialized to 0. Whether the semw semaphore control can be written, the initial value is 1.

The sample code for reading shared memory is as follows

Semr = sem_open ("mysem_r", O_CREAT | O_RDWR, 0666, 0); if (semr = = SEM_FAILED) {printf ("errno=%d\ n", errno); return-1;} semw = sem_open ("mysem_w", O_CREAT | O_RDWR, 0666, 1) If (semw = = SEM_FAILED) {printf ("errno=%d\ n", errno); return-1;} if ((shmid = shmget (key, MAXSIZE, 0666 | IPC_CREAT)) = =-1) {perror ("semget"); exit (- 1) } if ((shmadd = (char *) shmat (shmid, NULL, 0)) = (char *) (- 1) {perror ("shmat"); exit (- 1);} while (1) {em_wait (semr); printf ("% s\ n", shmadd); sem_post (semw) } the sample code for writing shared memory is as follows. / / the program while (1) {sem_wait (semw); printf (">"); fgets (shmadd, MAXSIZE, stdin); sem_post (semr); method 2. Using POSIX anonymous semaphores to achieve shared memory synchronization POSIX anonymous semaphores are memory-based semaphores that can be used for inter-thread synchronization or inter-process synchronization. To achieve inter-process synchronization, you need to create unnamed semaphores in shared memory.

Therefore, shared memory needs to define the following structures.

The typedef struct {sem_t semr; sem_t semw; char buf [MAXSIZE];} SHM; read and write program flow is shown in the following figure.

Method 3. Using the semaphore of System V to realize the synchronization of shared memory. The semaphore of System V is a collection of one or more semaphores. Each of them is a separate counting signal. The Posix semaphore refers to a single counting semaphore.

The System V semaphore is maintained by the kernel and the main function is semget,semop,semctl.

One process writes, the other process reads, there are two semaphores in the semaphore set, and the subscript 0 represents whether it can be read or not, initialized to 0. Subscript 1 represents whether it can be written, with an initial value of 1.

The program flow is as follows:

The process of writing is similar to the previous one.

Method 4. Using the signal to realize the synchronous signal of the shared memory is a kind of simulation of the interrupt mechanism at the software level, and it is a kind of asynchronous communication mode. The synchronization of shared memory can also be realized by using signals.

Train of thought:

Reader and writer must obtain each other's process number through signal communication, and the process number of both sides can be saved using shared memory.

The order in which reader and writer run is uncertain, so it can be agreed that the process that runs first creates shared memory and initializes it.

The program can be implemented by using pause, kill, signal and other functions (the process is similar to the previous one).

At this point, I believe you have a deeper understanding of "how to achieve shared memory synchronization in Linux". You might as well do it in practice. Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

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