h5响应式网站建设代理,wordpress密文,河源网站建设1993seo,帮忙做公司网站线程间通信之eventfd
man手册中的解释#xff1a; eventfd()创建了一个“eventfd对象”#xff0c; 通过它能够实现用户态程序间(我觉得这里主要指线程而非进程)的等待/通知机制#xff0c;以及内核态向用户态通知的机制#xff08;未考证#xff09;。 此对象包含了一个…线程间通信之eventfd
man手册中的解释 eventfd()创建了一个“eventfd对象” 通过它能够实现用户态程序间(我觉得这里主要指线程而非进程)的等待/通知机制以及内核态向用户态通知的机制未考证。 此对象包含了一个被内核所维护的计数uint64_t, 初始值由initval来决定。 int eventfd(unsigned int initval, int flags);创建一个eventfd文件描述符 int eventfd_read(int fd, eventfd_t *value); 向eventfd中写入一个值 int eventfd_write(int fd, eventfd_t value); 从eventfd中读出一个值
例一、子线程多次写入多个值主线程一次读出所有值的和 1 #include sys/eventfd.h2 #include unistd.h3 #include stdlib.h4 #include stdio.h5 #include stdint.h 6 7 int main(int argc, char**argv[])8 {9 int efd, j;
10 uint64_t u;
11 ssize_t s;
12
13 if (argc 2)
14 {
15 printf(number of argc is wrong!\n);
16 return 0;
17 }
18
19 efd eventfd(0,0);
20 if (-1 efd)
21 {
22 printf(failed to create eventfd\n);
23 }
24
25 switch(fork())
26 {
27 case 0:
28 {
29 for(j1; jargc;j)
30 {
31 printf(child writing %s to efd\n, argv[j]);
32 u strtoull(argv[j], NULL, 0);
33 s write(efd, u, sizeof(uint64_t));
34 if (s!sizeof(uint64_t))
35 {
36 printf(write efd failed\n);
37 }
38 }
39 printf(Child completed write loop\n);
40 exit(0);
41 }
42 default:
43 sleep(2);
44 printf(Parents about to read\n);
45 s read(efd, u, sizeof(uint64_t));
46 if (s ! sizeof(uint64_t))
47 {
48 printf(read efd failed\n);
49 }
50 printf(Parents first read %llu (0x%llx) from efd\n, u, u);
51 exit(0);
52 case -1:
53 {
54 printf(fork error\n);
55 }
56 }
57
58 return 0;
59 }
60
61 运行结果
62 kanekanelinux:/mnt/hgfs/kanelinuxshare/eventfd$ ./a.out 1 2 3 4
63 child writing 1 to efd
64 child writing 2 to efd
65 child writing 3 to efd
66 child writing 4 to efd
67 Child completed write loop
68 Parents about to read
69 Parents first read 10 (0xa) from efd
70
71 如果有写入操作但是并没有导致初始值变化则主线程会一直挂在read操作上
72 kanekanelinux:/mnt/hgfs/kanelinuxshare/eventfd$ ./a.out 0 0 0 0
73 child writing 0 to efd
74 child writing 0 to efd
75 child writing 0 to efd
76 child writing 0 to efd
77 Child completed write loop
78 Parents about to read
79 ^C 例二、eventfd可以被epoll监控 一旦有状态变化可以触发通知 1 #include sys/eventfd.h2 #include unistd.h3 #include stdlib.h4 #include stdio.h5 #include stdint.h 6 #include sys/epoll.h 7 #include string.h 8 #include pthread.h 9 10 int g_iEvtfd -1;11 12 void *eventfd_child_Task(void *pArg)13 {14 uint64_t uiWrite 1;15 16 while(1)17 {18 sleep(2);19 if (0 ! eventfd_write(g_iEvtfd, uiWrite))20 {21 printf(child write iEvtfd failed\n);22 } 23 }24 25 return;26 }27 28 int main(int argc, char**argv[])29 {30 int iEvtfd, j;31 uint64_t uiWrite 1;32 uint64_t uiRead;33 ssize_t s;34 int iEpfd;35 struct epoll_event stEvent;36 int iRet 0;37 struct epoll_event stEpEvent;38 pthread_t stWthread;39 40 iEpfd epoll_create(1);41 if (-1 iEpfd)42 {43 printf(Create epoll failed.\n);44 return 0;45 }46 47 iEvtfd eventfd(0,0);48 if (-1 iEvtfd)49 {50 printf(failed to create eventfd\n);51 return 0;52 }53 54 g_iEvtfd iEvtfd;55 56 memset(stEvent, 0, sizeof(struct epoll_event));57 stEvent.events (unsigned long) EPOLLIN;58 stEvent.data.fd iEvtfd;59 iRet epoll_ctl(iEpfd, EPOLL_CTL_ADD, g_iEvtfd, stEvent);60 if (0 ! iRet)61 {62 printf(failed to add iEvtfd to epoll\n);63 close(g_iEvtfd);64 close(iEpfd);65 return 0;66 }67 68 iRet pthread_create(stWthread, NULL, eventfd_child_Task, NULL);69 if (0 ! iRet)70 {71 close(g_iEvtfd);72 close(iEpfd);73 return;74 }75 76 for(;;)77 {78 iRet epoll_wait(iEpfd, stEpEvent, 1, -1);79 if (iRet 0)80 {81 s eventfd_read(iEvtfd, uiRead);82 if (s ! 0)83 {84 printf(read iEvtfd failed\n);85 break;86 }87 printf(Read %llu (0x%llx) from iEvtfd\n, uiRead, uiRead);88 }89 }90 91 close(g_iEvtfd);92 close(iEpfd);93 return 0;94 }95 运行结果96 kanekanelinux:/mnt/hgfs/kanelinuxshare/eventfd$ ./a.out97 Read 1 (0x1) from iEvtfd98 Read 1 (0x1) from iEvtfd99 Read 1 (0x1) from iEvtfd
100 Read 1 (0x1) from iEvtfd
101 Read 1 (0x1) from iEvtfd
102 Read 1 (0x1) from iEvtfd
103 Read 1 (0x1) from iEvtfd
104 Read 1 (0x1) from iEvtfd
105 ^C 例三、被epoll监控的eventfd如果在子线程中被多次写入在主线程中是怎么读的 #include sys/eventfd.h
#include unistd.h
#include stdlib.h
#include stdio.h
#include stdint.h
#include sys/epoll.h
#include string.h
#include pthread.h int g_iEvtfd -1;void *eventfd_child_Task(void *pArg)
{uint64_t uiWrite 1;while(1){sleep(2);eventfd_write(g_iEvtfd, uiWrite);eventfd_write(g_iEvtfd, uiWrite);}return;
}int main(int argc, char**argv[])
{int iEvtfd, j;uint64_t uiWrite 1;uint64_t uiRead;ssize_t s;int iEpfd;struct epoll_event stEvent;int iRet 0;struct epoll_event stEpEvent;pthread_t stWthread;iEpfd epoll_create(1);if (-1 iEpfd){printf(Create epoll failed.\n);return 0;}iEvtfd eventfd(0,0);if (-1 iEvtfd){printf(failed to create eventfd\n);return 0;}g_iEvtfd iEvtfd;memset(stEvent, 0, sizeof(struct epoll_event));stEvent.events (unsigned long) EPOLLIN;stEvent.data.fd iEvtfd;iRet epoll_ctl(iEpfd, EPOLL_CTL_ADD, g_iEvtfd, stEvent);if (0 ! iRet){printf(failed to add iEvtfd to epoll\n);close(g_iEvtfd);close(iEpfd);return 0;}iRet pthread_create(stWthread, NULL, eventfd_child_Task, NULL);if (0 ! iRet){close(g_iEvtfd);close(iEpfd);return;}for(;;){iRet epoll_wait(iEpfd, stEpEvent, 1, -1);if (iRet 0){s eventfd_read(iEvtfd, uiRead);if (s ! 0){printf(read iEvtfd failed\n);break;}printf(Read %llu (0x%llx) from iEvtfd\n, uiRead, uiRead);}}close(g_iEvtfd);close(iEpfd);return 0;
}运行结果
kanekanelinux:/mnt/hgfs/kanelinuxshare/eventfd$ ./a.out
Read 1 (0x1) from iEvtfd
Read 1 (0x1) from iEvtfdRead 1 (0x1) from iEvtfd
Read 1 (0x1) from iEvtfdRead 1 (0x1) from iEvtfd
Read 1 (0x1) from iEvtfdRead 1 (0x1) from iEvtfd
Read 1 (0x1) from iEvtfd^C 例一中并没有epoll做监控 因此在read前如果eventfd被写多次在read的时候也是一次全部读出。 注eventfd中的SEMAPHORE标志用法
* If EFD_SEMAPHORE was not specified and the eventfd counter has a nonzero value, then a read(2) returns 8 bytes contain‐ ing that value, and the counters value is reset to zero.
* If EFD_SEMAPHORE was specified and the eventfd counter has a nonzero value, then a read(2) returns 8 bytes containing the value 1, and the counters value is decremented by 1.
通过测试发现。如果eventfd在创建的时候传入EFD_SEMAPHORE 标志则会按上面man手册中提到的那样每次在eventfd_read的时候只减一并不是把值一次性全部读出。见下例
