好久没更新了，今天看一下第三种新的fd：eventfd类似于管道的概念，可以实现线程间的事件通知，所不同的是eventfd的缓冲区大小是sizeof(uint64_t)也就是8字节，它是一个64位的计数器，写入递增计数器，读取将得到计数器的值，并且清零。看一下代码：
- #include <sys/eventfd.h>
- #include <unistd.h>
- #include <stdlib.h>
- #include <stdio.h>
- #include <stdint.h> /* Definition of uint64_t */
- #define handle_error(msg) \
- do { perror(msg); exit(EXIT_FAILURE); } while (0)
- int
- main(int argc, char *argv[])
- {
- uint64_t u;
- int efd = eventfd(10, 0);
- if (efd == -1)
- handle_error("eventfd");
- int ret = fork();
- if(ret == 0)
- {
- for (int j = 1; j < argc; j++) {
- printf("Child writing %s to efd\n", argv[j]);
- u = atoll(argv[j]);
- ssize_t s = write(efd, &u, sizeof(uint64_t));
- if (s != sizeof(uint64_t))
- handle_error("write");
- }
- printf("Child completed write loop\n");
- exit(EXIT_SUCCESS);
- }
- else
- {
- sleep(2);
- ssize_t s = read(efd, &u, sizeof(uint64_t));
- if (s != sizeof(uint64_t))
- handle_error("read");
- printf("Parent read %llu from efd\n",(unsigned long long)u);
- exit(EXIT_SUCCESS);
- }
- }
运行结果：
- ./eventfd 10 20 30
- Child writing 10 to efd
- Child writing 20 to efd
- Child writing 30 to efd
- Child completed write loop
- Parent read 70 from efd
