新版本glib使用epoll代替poll

新版本的glib支持使用外部的事件循环代替内部的poll，这篇文章使用的glib版本是V2.72.0, 理解还很粗浅，但是demo能跑起来，还需要再详细研究一下参考的两个链接，多线程下使用及效率是怎样的都还不清楚。

1、新API

通过新的API g_main_context_new_with_flags 及新变量G_MAIN_CONTEXT_FLAGS_OWNERLESS_POLLING可以创建一个无主的poll，然后通过glib的一套API可以实现自己的事件循环。ubuntu18下的demo：

#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <dirent.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/time.h>
#include <glib.h>
#include <sys/epoll.h>static GMainContext *watchdog_context = NULL;int num = 0;
static gboolean cb_check(gpointer user_data)
{printf("In cb_check %d \n", num);
}char* name = "ori";
static gpointer cb_watchdog(gpointer user_data)
{num = 1;GMainLoop *loop = (GMainLoop *) user_data;GMainContext *watchdog_context = g_main_loop_get_context(loop);GSource *timeout_source;timeout_source = g_timeout_source_new_seconds(2);g_source_set_callback(timeout_source, cb_check, watchdog_context, (gpointer)name);g_source_attach(timeout_source, watchdog_context);g_source_unref(timeout_source);printf("Sessions watchdog started\n");g_main_loop_run(loop);printf("Sessions watchdog stopped\n");return NULL;
}void test_ori_glib_event_loop()
{/* Start the sessions timeout watchdog */watchdog_context = g_main_context_new();GError *error = NULL;GMainLoop *watchdog_loop = g_main_loop_new(watchdog_context, FALSE);GThread *watchdog = g_thread_try_new("timeout watchdog", &cb_watchdog, watchdog_loop, &error);if(error != NULL) {printf("Got error %d (%s) trying to start sessions timeout watchdog...\n",error->code, error->message ? error->message : "??");g_error_free(error);exit(1);}
}unsigned short glib_event_2_epoll(unsigned short  glib_event)
{unsigned short ret = 0;if (glib_event & G_IO_IN)ret |= EPOLLIN;if (glib_event & G_IO_OUT)ret |= EPOLLOUT;if (glib_event & G_IO_PRI)ret |= EPOLLPRI;if (glib_event & G_IO_HUP)ret |= EPOLLHUP;if (glib_event & G_IO_NVAL)ret |= EPOLLERR;return ret;
}unsigned short epoll_event_2_glib(unsigned short  epoll_event)
{unsigned short ret = 0;if (epoll_event & EPOLLIN) ret |= G_IO_IN;if (epoll_event & EPOLLOUT)ret |= G_IO_OUT ;if (epoll_event & EPOLLPRI)ret |= G_IO_PRI;if (epoll_event & EPOLLHUP)ret |= G_IO_HUP;if (epoll_event & EPOLLERR)ret |= G_IO_NVAL;return ret;
}#define MAX_EVENTS (4096)
int ev_poll(GPollFD *fds,guint    nfds,gint     timeout)
{GPollFD *f = NULL;int epollfd = -1;struct epoll_event  ev;int ret = 0;int max_events = nfds;struct epoll_event epoll_events[MAX_EVENTS];for (f = fds; f < &fds[nfds]; ++f){if (f->fd >= 0){if(epollfd == -1){epollfd = epoll_create1(EPOLL_CLOEXEC);if ( epollfd == -1 ){perror( "epoll_create1" );continue;}}ev.events  = f->events;//glib_event_2_epoll(f->events);ev.data.fd = f->fd;if( epoll_ctl(epollfd, EPOLL_CTL_ADD, f->fd, &ev) == -1 ){perror( "epoll_ctl: listen_sock" );continue;}}}nfds = epoll_wait( epollfd, epoll_events, MAX_EVENTS, 10 );if(nfds > 0){//unsigned short events = event[i].events;struct epoll_event  *ev = NULL;for (ev = epoll_events; ev < &epoll_events[nfds]; ++ev){f->revents = 0;if (f->fd >= 0){f->revents = ev->events;//epoll_event_2_glib(ev->events);}}}else{perror( "epoll_wait" );return 0;}if(epollfd != -1){close(epollfd);}return nfds;
}char* evname = "ev_ori";
/* epoll实现的事件侦听及处理 */
void test_ev_glib_event_loop()
{num = 2;/* Start the sessions timeout watchdog */GMainContext *ctx = g_main_context_new_with_flags (G_MAIN_CONTEXT_FLAGS_OWNERLESS_POLLING);g_main_context_push_thread_default (ctx);GPollFD fds[20];gint fds_size;gint max_priority;GSource *source = NULL;GSource *timeout_source;timeout_source = g_timeout_source_new_seconds(2);g_source_set_callback(timeout_source, cb_check, ctx, (gpointer)evname);g_source_attach(timeout_source, ctx);g_source_unref(timeout_source);for(;;){gboolean ready_to_dispatch = g_main_context_prepare (ctx, &max_priority);gint timeout, nready;fds_size = g_main_context_query (ctx, max_priority, &timeout, fds, G_N_ELEMENTS (fds));//nready = g_poll (fds, fds_size, /*timeout=*/0);nready = ev_poll (fds, fds_size, /*timeout=*/0);if (!ready_to_dispatch && nready == 0){if (timeout == -1)break;elseg_usleep (timeout * 1000);}if(fds_size == 1)printf("events %d \n", fds[0].events);printf("events G_IO_IN[%d] G_IO_OUT[%d] G_IO_PRI[%d]\n", G_IO_IN, G_IO_OUT, G_IO_PRI);ready_to_dispatch = g_main_context_check (ctx, max_priority, fds, fds_size);if (ready_to_dispatch)g_main_context_dispatch (ctx);}g_assert_cmpint (g_poll (fds, fds_size, 0), >, 0);g_main_context_unref (ctx);
}int main()
{//test_ori_glib_event_loop();test_ev_glib_event_loop();while(1){sleep(1);}return 0;
}

编译

gcc -o demo_glib main.c -lpthread `pkg-config --cflags glib-2.0` `pkg-config --libs glib-2.0`

2、参考

《1》、Pluggable event loop backends (epoll support)
《2》、Add g_main_context_new_with_flags() and ownerless polling option

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新版本glib使用epoll代替poll

1、新API

2、参考

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