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| author | Michael Kerrisk <mtk.manpages@gmail.com> | 2020-02-18 11:14:45 +0100 |
|---|---|---|
| committer | Michael Kerrisk <mtk.manpages@gmail.com> | 2020-02-18 22:59:35 +0100 |
| commit | c9a275a703d37eea1724f12f95e0d592fbed79c3 (patch) | |
| tree | 2c7d1c77744cde8a274c33eff38f61dffe820234 /man2/select_tut.2 | |
| parent | b3b45b2b16bfb0eb29906cfeb9cea66f3cb79aab (diff) | |
| download | man-pages-c9a275a703d37eea1724f12f95e0d592fbed79c3.tar.gz | |
select_tut.2: DESCRIPTION: defer to select(2)
Avoid duplicating the same information in two pages.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Diffstat (limited to 'man2/select_tut.2')
| -rw-r--r-- | man2/select_tut.2 | 138 |
1 files changed, 9 insertions, 129 deletions
diff --git a/man2/select_tut.2 b/man2/select_tut.2 index eaad9cb117..f608a1f2fb 100644 --- a/man2/select_tut.2 +++ b/man2/select_tut.2 @@ -31,8 +31,7 @@ .\" .TH SELECT_TUT 2 2019-03-06 "Linux" "Linux Programmer's Manual" .SH NAME -select, pselect, FD_CLR, FD_ISSET, FD_SET, FD_ZERO \- -synchronous I/O multiplexing +select, pselect \- synchronous I/O multiplexing .SH SYNOPSIS .PP See @@ -46,135 +45,16 @@ to see if any of them is, or becomes, "ready"; that is, to see whether I/O becomes possible, or an "exceptional condition" has occurred on any of the file descriptors. .PP -Its principal arguments are three "sets" of file descriptors: -\fIreadfds\fP, \fIwritefds\fP, and \fIexceptfds\fP. -Each set is declared as type -.IR fd_set , -and its contents can be manipulated with the macros -.BR FD_CLR (), -.BR FD_ISSET (), -.BR FD_SET (), -and -.BR FD_ZERO (). -A newly declared set should first be cleared using -.BR FD_ZERO (). -.BR select () -modifies the contents of the sets according to the rules -described below; after calling -.BR select () -you can test if a file descriptor is still present in a set with the -.BR FD_ISSET () -macro. -.BR FD_ISSET () -returns nonzero if a specified file descriptor is present in a set -and zero if it is not. -.BR FD_CLR () -removes a file descriptor from a set. -.SS Arguments -.TP -\fIreadfds\fP -This set is watched to see if data is available for reading from any of -its file descriptors. -After +This page provides background and tutorial information +on the use of these system calls. +For details of the arguments and semantics of .BR select () -has returned, \fIreadfds\fP will be -cleared of all file descriptors except for those that -are immediately available for reading. -.TP -\fIwritefds\fP -This set is watched to see if there is space to write data to any of -its file descriptors. -After -.BR select () -has returned, \fIwritefds\fP will be -cleared of all file descriptors except for those that -are immediately available for writing. -.TP -\fIexceptfds\fP -This set is watched for "exceptional conditions". -In practice, only one such exceptional condition is common: -the availability of \fIout-of-band\fP (OOB) data for reading -from a TCP socket. -See -.BR recv (2), -.BR send (2), and -.BR tcp (7) -for more details about OOB data. -(One other less common case where -.BR select (2) -indicates an exceptional condition occurs with pseudoterminals -in packet mode; see -.BR ioctl_tty (2).) -After -.BR select () -has returned, -\fIexceptfds\fP will be cleared of all file descriptors except for those -for which an exceptional condition has occurred. -.TP -\fInfds\fP -This is an integer one more than the maximum of any file descriptor in -any of the sets. -In other words, while adding file descriptors to each of the sets, -you must calculate the maximum integer value of all of them, -then increment this value by one, and then pass this as \fInfds\fP. -.TP -\fIutimeout\fP -This is the longest time -.BR select () -may wait before returning, even if nothing interesting happened. -If this value is passed as NULL, then -.BR select () -blocks indefinitely waiting for a file descriptor to become ready. -\fIutimeout\fP can be set to zero seconds, which causes -.BR select () -to return immediately, with information about the readiness -of file descriptors at the time of the call. -The structure \fIstruct timeval\fP is defined as: -.IP -.in +4n -.EX -struct timeval { - time_t tv_sec; /* seconds */ - long tv_usec; /* microseconds */ -}; -.EE -.in -.TP -\fIntimeout\fP -This argument for -.BR pselect () -has the same meaning as -.IR utimeout , -but -.I "struct timespec" -has nanosecond precision as follows: -.IP -.in +4n -.EX -struct timespec { - long tv_sec; /* seconds */ - long tv_nsec; /* nanoseconds */ -}; -.EE -.in -.TP -\fIsigmask\fP -This argument holds a set of signals that the kernel should unblock -(i.e., remove from the signal mask of the calling thread), -while the caller is blocked inside the -.BR pselect () -call (see -.BR sigaddset (3) -and -.BR sigprocmask (2)). -It may be NULL, -in which case the call does not modify the signal mask on -entry and exit to the function. -In this case, -.BR pselect () -will then behave just like -.BR select (). +.BR pselect (), +see +.BR select (2). +.PP +.\" .SS Combining signal and data events .BR pselect () is useful if you are waiting for a signal as well as |