文章目录API说明举例API说明•eventfd API •int eventfd(unsigned int initval, int flags); –用来创建一个用于事件通知的eventfd对象 –返回值为一个int型fd用来引用打开的对象 –打开的对象在内核中是一个64位的无符号整型计数器初始化为initval –计数器数据类型typedef uint64_t eventfd_t •flags: –EFD_CLOEXEC类似于open的flagsfork子进程时不继承 –EFD_NONBLOCK一般会设置成非阻塞 –EFD_SEMAPHORE信号量语义的read每次读操作计时器值减1 •内核实现fs/eventfd.c举例#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[]) { int fd_event, j; uint64_t u; ssize_t s; if (argc 2) { fprintf (stderr, Usage: %s num...\n, argv[0]); exit (EXIT_FAILURE); } fd_event eventfd(0, EFD_SEMAPHORE); if (fd_event -1) handle_error (eventfd); switch (fork()) { case 0: sleep (1); for (j 1; j argc; j) { printf (Child writing %s to fd_event\n, argv[j]); u strtoull (argv[j], NULL, 0); /* strtoull() allows various bases */ s write (fd_event, u, sizeof(uint64_t)); if (s ! sizeof(uint64_t)) handle_error (write); } printf (Child completed write loop\n); exit (EXIT_SUCCESS); default: // sleep (2); printf (Parent about to read\n); s read (fd_event, u, sizeof(uint64_t)); if (s ! sizeof(uint64_t)) handle_error (read); printf (Parent read %llu (0x%llx) from fd_event\n, (unsigned long long) u, (unsigned long long) u); s read (fd_event, u, sizeof(uint64_t)); if (s ! sizeof(uint64_t)) handle_error (read); printf (Parent read %llu (0x%llx) from fd_event\n, (unsigned long long) u, (unsigned long long) u); s read (fd_event, u, sizeof(uint64_t)); if (s ! sizeof(uint64_t)) handle_error (read); printf (Parent read %llu (0x%llx) from fd_event\n, (unsigned long long) u, (unsigned long long) u); exit (EXIT_SUCCESS); case -1: handle_error (fork); } } // ./a.out 1 2 3 4 5 6 7 8 9