您的架構是明智的,它會工作:epoll
將文件描述符標記爲可讀並觸發EPOLLIN
事件。
關於這方面的文檔是稀缺和微妙的;在Q/man 7 epoll
簡要的部分提到這一點:
Q8是否對文件描述符的操作影響已收集 但尚未報告的事件?
A8您可以在 現有文件描述符上執行兩個操作。刪除對於這種情況將毫無意義。 修改將重讀可用的I/O。
兩個操作,您可以在現有的文件描述符做(現有的文件描述符已被添加到在過去設定的epoll的文件描述符 - 這包括正在等待重新裝備文件描述符)被刪除和修改。正如手冊頁提到的,刪除在這裏沒有意義,修改將重新評估文件描述符中的條件。
儘管如此,沒有什麼比現實世界的實驗更勝一籌。下面的程序測試該邊緣的情況下:
#include <stdio.h>
#include <pthread.h>
#include <signal.h>
#include <stdlib.h>
#include <assert.h>
#include <semaphore.h>
#include <sys/epoll.h>
#include <unistd.h>
static pthread_t tids[2];
static int epoll_fd;
static char input_buff[512];
static sem_t chunks_sem;
void *dispatcher(void *arg) {
struct epoll_event epevent;
while (1) {
printf("Dispatcher waiting for more chunks\n");
if (epoll_wait(epoll_fd, &epevent, 1, -1) < 0) {
perror("epoll_wait(2) error");
exit(EXIT_FAILURE);
}
ssize_t n;
if ((n = read(STDIN_FILENO, input_buff, sizeof(input_buff)-1)) <= 0) {
if (n < 0)
perror("read(2) error");
else
fprintf(stderr, "stdin closed prematurely\n");
exit(EXIT_FAILURE);
}
input_buff[n] = '\0';
sem_post(&chunks_sem);
}
return NULL;
}
void *consumer(void *arg) {
sigset_t smask;
sigemptyset(&smask);
sigaddset(&smask, SIGUSR1);
while (1) {
sem_wait(&chunks_sem);
printf("Consumer received chunk: %s", input_buff);
/* Simulate some processing... */
sleep(2);
printf("Consumer finished processing chunk.\n");
printf("Please send SIGUSR1 after sending more data to stdin\n");
int signo;
if (sigwait(&smask, &signo) < 0) {
perror("sigwait(3) error");
exit(EXIT_FAILURE);
}
assert(signo == SIGUSR1);
struct epoll_event epevent;
epevent.events = EPOLLIN | EPOLLONESHOT;
epevent.data.fd = STDIN_FILENO;
if (epoll_ctl(epoll_fd, EPOLL_CTL_MOD, STDIN_FILENO, &epevent) < 0) {
perror("epoll_ctl(2) error when attempting to readd stdin");
exit(EXIT_FAILURE);
}
printf("Readded stdin to epoll fd\n");
}
}
int main(void) {
sigset_t sigmask;
sigfillset(&sigmask);
if (pthread_sigmask(SIG_SETMASK, &sigmask, NULL) < 0) {
perror("pthread_sigmask(3) error");
exit(EXIT_FAILURE);
}
if ((epoll_fd = epoll_create(1)) < 0) {
perror("epoll_create(2) error");
exit(EXIT_FAILURE);
}
struct epoll_event epevent;
epevent.events = EPOLLIN | EPOLLONESHOT;
epevent.data.fd = STDIN_FILENO;
if (epoll_ctl(epoll_fd, EPOLL_CTL_ADD, STDIN_FILENO, &epevent) < 0) {
perror("epoll_ctl(2) error");
exit(EXIT_FAILURE);
}
if (sem_init(&chunks_sem, 0, 0) < 0) {
perror("sem_init(3) error");
exit(EXIT_FAILURE);
}
if (pthread_create(&tids[0], NULL, dispatcher, NULL) < 0) {
perror("pthread_create(3) error on dispatcher");
exit(EXIT_FAILURE);
}
if (pthread_create(&tids[1], NULL, consumer, NULL) < 0) {
perror("pthread_create(3) error on consumer");
exit(EXIT_FAILURE);
}
size_t i;
for (i = 0; i < sizeof(tids)/sizeof(tids[0]); i++) {
if (pthread_join(tids[i], NULL) < 0) {
perror("pthread_join(3) error");
exit(EXIT_FAILURE);
}
}
return 0;
}
它的工作原理如下:在調度程序線程添加stdin
到epoll的集合,然後使用epoll_wait(2)
每當它變爲可讀從stdin
取輸入。當輸入到達時,調度員喚醒工作線程,他打印輸入並通過睡眠2秒來模擬一些處理時間。同時,調度程序返回到主循環並再次在epoll_wait(2)
中阻止。
工作者線程將不會重新編譯stdin
,直到您通過發送它SIGUSR1
來告訴它。所以,我們只是寫更多的東西到stdin
,然後發送SIGUSR1
的過程。工作線程收到信號,然後才重新加載stdin
- 這個時間已經可讀,調度程序已經在等待epoll_wait(2)
。
您可以從輸出中看到,調度員正確喚醒,一切工作就像一個魅力:
Dispatcher waiting for more chunks
testing 1 2 3 // Input
Dispatcher waiting for more chunks // Dispatcher notified worker and is waiting again
Consumer received chunk: testing 1 2 3
Consumer finished processing chunk.
Please send SIGUSR1 after sending more data to stdin
hello world // Input
Readded stdin to epoll fd // Rearm stdin; dispatcher is already waiting
Dispatcher waiting for more chunks // Dispatcher saw new input and is now waiting again
Consumer received chunk: hello world
Consumer finished processing chunk.
Please send SIGUSR1 after sending more data to stdin