diff --git a/shm_open/build.zig b/shm_open/build.zig new file mode 100644 index 0000000..94a57dd --- /dev/null +++ b/shm_open/build.zig @@ -0,0 +1,20 @@ +const std = @import("std"); + +pub fn build(b: *std.build.Builder) void { + const target = b.standardTargetOptions(.{}); + const optimize = b.standardOptimizeOption(.{}); + + const exe = b.addExecutable(.{ + .name = "shm-open-example", + .root_source_file = .{ .path = "main.c" }, + .optimize = optimize, + .target = target + }); + exe.linkLibC(); + + const run_cmd = b.addRunArtifact(exe); + const run_step = b.step("run", "Run simple program"); + run_step.dependOn(&run_cmd.step); + + b.installArtifact(exe); +} diff --git a/shm_open/main.c b/shm_open/main.c new file mode 100644 index 0000000..8f283a9 --- /dev/null +++ b/shm_open/main.c @@ -0,0 +1,125 @@ +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#define SHM_NAME "/shared_memory" + +struct shared_data { + pthread_mutex_t mutex; + int counter; +}; + +struct shm_shared_data { + int shm_fd; + struct shared_data *shared_data; +}; + +void increment_counter(struct shared_data *data) { + for (int i = 0; i < 100000; i++) { + if (pthread_mutex_lock(&data->mutex) != 0) { + perror("pthread_mutex_lock"); + } + + data->counter++; + + if (pthread_mutex_unlock(&data->mutex) != 0) { + perror("pthread_mutex_unlock"); + } + } +} + +struct shm_shared_data shared_data_open() { + struct shared_data *shared_data; + + // Create or open a shared memory object + int shm_fd = shm_open(SHM_NAME, O_CREAT | O_RDWR, S_IRUSR | S_IWUSR); + if (shm_fd == -1) { + perror("shm_open"); + exit(EXIT_FAILURE); + } + + int shm_size = sizeof(struct shared_data); + + if (ftruncate(shm_fd, shm_size) == -1) { + perror("ftruncate"); + exit(EXIT_FAILURE); + } + + // Map the shared memory object into the process's address space + shared_data = mmap(NULL, shm_size, PROT_READ | PROT_WRITE, MAP_SHARED, shm_fd, 0); + if (shared_data == MAP_FAILED) { + perror("mmap"); + exit(EXIT_FAILURE); + } + + struct shm_shared_data shm_shared_data = { + .shm_fd = shm_fd, + .shared_data = shared_data + }; + + return shm_shared_data; +} + +void shared_data_close(struct shm_shared_data shm_data) { + // Unmap the shared memory and close the file descriptor + if (munmap(shm_data.shared_data, sizeof(struct shared_data)) == -1) { + perror("munmap"); + exit(EXIT_FAILURE); + } + + if (close(shm_data.shm_fd) == -1) { + perror("close"); + exit(EXIT_FAILURE); + } +} + +void *thread_callback(void *p) { + struct shm_shared_data shm_data = shared_data_open(); + + increment_counter(shm_data.shared_data); + + shared_data_close(shm_data); + + return NULL; +} + +int main() { + struct shm_shared_data shm_data = shared_data_open(); + + pthread_mutexattr_t mutex_attr; + pthread_mutexattr_init(&mutex_attr); + pthread_mutexattr_setpshared(&mutex_attr, PTHREAD_PROCESS_SHARED); + + if (pthread_mutex_init(&shm_data.shared_data->mutex, &mutex_attr) < 0) { + printf("Failed to initialise mutex\n"); + return -1; + } + + pthread_t thread1; + pthread_create(&thread1, NULL, thread_callback, NULL); + + pthread_t thread2; + pthread_create(&thread2, NULL, thread_callback, NULL); + + pthread_join(thread1, NULL); + pthread_join(thread2, NULL); + + printf("Counter is %d\n", shm_data.shared_data->counter); + + shared_data_close(shm_data); + + // Unlink the shared memory object (aka delete shared memory) + if (shm_unlink(SHM_NAME) == -1) { + perror("shm_unlink"); + exit(EXIT_FAILURE); + } + + return 0; +}