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最新推荐文章于 2025-05-11 17:35:37 发布

转载最新推荐文章于 2025-05-11 17:35:37 发布 · 897 阅读

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1. epoll_create

NAME
       epoll_create open an epoll file descriptor

SYNOPSIS
       #include <sys/epoll.h>
       int epoll_create(int size);

DESCRIPTION
       epoll_create() creates an epoll "instance", requesting the kernel to allocate an event backing store dimen‐
       sioned for size descriptors. The size is not the maximum size of the backing store but just a hint to the
       kernel about how to dimension internal structures. (Nowadays, size is ignored; see NOTES below.)

       epoll_create() returns a file descriptor referring to the new epoll instance. This file descriptor is used
       for all the subsequent calls to the epoll interface. When no longer required, the file descriptor returned by
       epoll_create() should be closed by using close(2). When all file descriptors referring to an epoll instance
       have been closed, the kernel destroys the instance and releases the associated resources for re-use.

RETURN VALUE
       On success, these system calls return a non-negative file descriptor. On error, -1 is returned, and errno is
       set to indicate the error.

2. poll_ctl

NAME
       epoll_ctl - control interface for an epoll descriptor

SYNOPSIS
       #include <sys/epoll.h>
       int epoll_ctl(int epfd, int op, int fd, struct epoll_event *event);

DESCRIPTION
       This system call performs control operations on the epoll instance referred to by the file descriptor epfd.
       It requests that the operation op be performed for the target file descriptor, fd.

       Valid values for the op argument are :

       EPOLL_CTL_ADD
              Register the target file descriptor fd on the epoll instance referred to by the file descriptor epfd
              and associate the event event with the internal file linked to fd.

       EPOLL_CTL_MOD
              Change the event event associated with the target file descriptor fd.

       EPOLL_CTL_DEL
              Remove (deregister) the target file descriptor fd from the epoll instance referred to by epfd. The
              event is ignored and can be NULL (but see BUGS below).

       The event argument describes the object linked to the file descriptor fd. The struct epoll_event is defined
       as :

           typedef union epoll_data {
               void        *ptr;
               int          fd;
               __uint32_t   u32;
               __uint64_t   u64;
           } epoll_data_t;

           struct epoll_event {
               __uint32_t   events;      /* Epoll events */
               epoll_data_t data;        /* User data variable */
           };

       The events member is a bit set composed using the following available event types:

       EPOLLIN
              The associated file is available for read(2) operations.

       EPOLLOUT
              The associated file is available for write(2) operations.

       EPOLLRDHUP (since Linux 2.6.17)
              Stream socket peer closed connection, or shut down writing half of connection. (This flag is espe‐
              cially useful for writing simple code to detect peer shutdown when using Edge Triggered monitoring.)

       EPOLLPRI
              There is urgent data available for read(2) operations.

       EPOLLERR
              Error condition happened on the associated file descriptor. epoll_wait(2) will always wait for this
              event; it is not necessary to set it in events.

       EPOLLHUP
              Hang up happened on the associated file descriptor. epoll_wait(2) will always wait for this event; it
              is not necessary to set it in events.

       EPOLLET
              Sets the Edge Triggered behavior for the associated file descriptor. The default behavior for epoll is
              Level Triggered. See epoll(7) for more detailed information about Edge and Level Triggered event dis‐
              tribution architectures.

       EPOLLONESHOT (since Linux 2.6.2)
              Sets the one-shot behavior for the associated file descriptor. This means that after an event is
              pulled out with epoll_wait(2) the associated file descriptor is internally disabled and no other events
              will be reported by the epoll interface. The user must call epoll_ctl() with EPOLL_CTL_MOD to re-arm
              the file descriptor with a new event mask.

RETURN VALUE
       When successful, epoll_ctl() returns zero.   When an error occurs, epoll_ctl() returns -1 and errno is set
       appropriately.

3. epoll_wait

NAME
       epoll_wait - wait for an I/O event on an epoll file descriptor

SYNOPSIS
       #include <sys/epoll.h>
       int epoll_wait(int epfd, struct epoll_event *events,
                      int maxevents, int timeout);

DESCRIPTION
       The epoll_wait() system call waits for events on the epoll instance referred to by the file descriptor epfd.
       The memory area pointed to by events will contain the events that will be available for the caller.   Up to
       maxevents are returned by epoll_wait(). The maxevents argument must be greater than zero.

       The call waits for a maximum time of timeout milliseconds. Specifying a timeout of -1 makes epoll_wait() wait
       indefinitely, while specifying a timeout equal to zero makes epoll_wait() to return immediately even if no
       events are available (return code equal to zero).

       The data of each returned structure will contain the same data the user set with an epoll_ctl(2)
       (EPOLL_CTL_ADD,EPOLL_CTL_MOD) while the events member will contain the returned event bit field.

RETURN VALUE
       When successful, epoll_wait() returns the number of file descriptors ready for the requested I/O, or zero if
       no file descriptor became ready during the requested timeout milliseconds. When an error occurs, epoll_wait()
       returns -1 and errno is set appropriately.