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select

SYNOPSIS

int select(int numfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);

Macro utilities:

FD_CLR(int fd, fd_set *set);

FD_ISSET(int fd, fd_set *set);

FD_SET(int fd, fd_set *set);

FD_ZERO(fd_set *set);

PARAMETERS

numfds: [in] the number of file descriptors to watch.

readfds: [in out] on entry, the file descriptor to watch for readability. On exit, the file descriptors that are readable.

writefds: [in out] on entry, the file descriptors to watch for writability. On exit, the file descriptors that are writable.

exceptfds: [in out] on entry, the file descriptor to watch exceptions. On exit, the file descriptors have exceptions raised.

timeout: [in out] on entry, the timeout value. On return, contains the remaining time.

DESCRIPTION

Makes the calling task sleep until some conditions on the file descriptors become true or until a timeout value expires. There are three conditions for which files may be tested:

• with readfds: Can the file be read?
• with writefds: Can the file be written?
• with exceptfds: Is there any exception pending on the file?

Whenever one of the conditions on one the specified files is true, the call returns.

There are four utilities provided for manipulation of the file descriptor sets:

FD_SET

sets the specified file descriptor flag.

FD_CLR

clears the specified file descriptor flag.

FD_ZERO

clears the set.

FD_ISSET

returns true if the file descriptor flag is set.

RETURN VALUE

On success, returns zero. On error, returns -1 and sets errno to one of the following value:

• EBADF, EINTR, EINVAL or ENOMEM

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