#include <sys/epoll.h>
int epoll_wait(int epfd, struct epoll_event *events,
int maxevents, int timeout);
int epoll_pwait(int epfd, struct epoll_event *events,
int maxevents, int timeout,
const sigset_t *sigmask);
The timeout argument specifies the number of milliseconds that epoll_wait() will block. Time is measured against the CLOCK_MONOTONIC clock.
A call to epoll_wait() will block until either:
timeout 時間はシステムクロックの粒度に切り上げられ、カーネルのスケジューリング遅延により少しだけ長くなる可能性がある点に注意すること。 timeout を -1 に指定すると、 epoll_wait() は無限に停止する。 timeout を 0 に指定すると、 epoll_wait() は利用可能なイベントがなくても、すぐに返る。
struct epoll_event は以下のように定義される。
typedef union epoll_data {
void *ptr;
int fd;
uint32_t u32;
uint64_t u64; } epoll_data_t;
struct epoll_event {
uint32_t events; /* epoll イベント */
epoll_data_t data; /* ユーザーデータ変数 */ };
The data field of each returned epoll_event structure contains the same data as was specified in the most recent call to epoll_ctl(2) (EPOLL_CTL_ADD, EPOLL_CTL_MOD) for the corresponding open file descriptor.
The events field is a bit mask that indicates the events that have occurred for the corresponding open file description. See epoll_ctl(2) for a list of the bits that may appear in this mask.
以下の epoll_pwait() の呼び出しは、
ready = epoll_pwait(epfd, &events, maxevents, timeout, &sigmask);
次の呼び出しを atomic に実行するのと等価である。
sigset_t origmask;
pthread_sigmask(SIG_SETMASK, &sigmask, &origmask); ready = epoll_wait(epfd, &events, maxevents, timeout); pthread_sigmask(SIG_SETMASK, &origmask, NULL);
sigmask 引数には NULL を指定してもよい。 その場合には、 epoll_pwait() は epoll_wait() と等価となる。
epoll_pwait() はカーネル 2.6.19 で Linux に追加された。 ライブラリによるサポートは glibc バージョン 2.6 以降で提供されている。
If more than maxevents file descriptors are ready when epoll_wait() is called, then successive epoll_wait() calls will round robin through the set of ready file descriptors. This behavior helps avoid starvation scenarios, where a process fails to notice that additional file descriptors are ready because it focuses on a set of file descriptors that are already known to be ready.
Note that it is possible to call epoll_wait() on an epoll instance whose interest list is currently empty (or whose interest list becomes empty because file descriptors are closed or removed from the interest in another thread). The call will block until some file descriptor is later added to the interest list (in another thread) and that file descriptor becomes ready.
[man1]
[man2]
[man3]
[man4]
[man5]
[man6]
[man7]
[man8]
[a]
[b]
[c]
[d]
[e]
[f]
[g]
[h]
[i]
[j]
[k]
[l]
[m]
[n]
[o]
[p]
[q]
[r]
[s]
[t]
[u]
[v]
[w]
[x]
[y]
[z]