man2/sigwaitinfo.2

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  20 .TH SIGWAITINFO 2 2007-07-26 "Linux" "Linux Programmer's Manual"
  21 .SH NAME
  22 sigwaitinfo, sigtimedwait \- synchronously wait for queued signals
  23 .SH SYNOPSIS
  24 .nf
  25 .B #include <signal.h>
  26 .sp
  27 .BI "int sigwaitinfo(const sigset_t *" set ", siginfo_t *" info ");"
  28 .sp
  29 .BI "int sigtimedwait(const sigset_t *" set ", siginfo_t *" info ", "
  30 .BI "                 const struct timespec *" timeout ");"
  31 .fi
  32 .sp
  33 .in -4n
  34 Feature Test Macro Requirements for glibc (see
  35 .BR feature_test_macros (7)):
  36 .in
  37 .sp
  38 .BR sigwaitinfo (),
  39 .BR sigtimedwait ():
  40 _POSIX_C_SOURCE\ >=\ 199309L
  41 .SH DESCRIPTION
  42 .BR sigwaitinfo ()
  43 suspends execution of the calling process until one of the signals in
  44 .I set
  45 is delivered.
  46 (If one of the signals in
  47 .I set
  48 is already pending for the calling process,
  49 .BR sigwaitinfo ()
  50 will return immediately with information about that signal.)
  51
  52 .BR sigwaitinfo ()
  53 removes the delivered signal from the calling process's list of pending
  54 signals and returns the signal number as its function result.
  55 If the
  56 .I info
  57 argument is not NULL,
  58 then it returns a structure of type
  59 .I siginfo_t
  60 (see
  61 .BR sigaction (2))
  62 containing information about the signal.
  63 .PP
  64 Signals returned via
  65 .BR sigwaitinfo ()
  66 are delivered in the usual order; see
  67 .BR signal (7)
  68 for further details.
  69 .PP
  70 .BR sigtimedwait ()
  71 operates in exactly the same way as
  72 .BR sigwaitinfo ()
  73 except that it has an additional argument,
  74 .IR timeout ,
  75 which enables an upper bound to be placed on the time for which
  76 the process is suspended.
  77 This argument is of the following type:
  78 .sp
  79 .in +4n
  80 .nf
  81 struct timespec {
  82     long    tv_sec;         /* seconds */
  83     long    tv_nsec;        /* nanoseconds */
  84 }
  85 .fi
  86 .in
  87 .sp
  88 If both fields of this structure are specified as 0, a poll is performed:
  89 .BR sigtimedwait ()
  90 returns immediately, either with information about a signal that
  91 was pending for the caller, or with an error
  92 if none of the signals in
  93 .I set
  94 was pending.
  95 .SH "RETURN VALUE"
  96 On success, both
  97 .BR sigwaitinfo ()
  98 and
  99 .BR sigtimedwait ()
 100 return a signal number (i.e., a value greater than zero).
 101 On failure both calls return \-1, with
 102 .I errno
 103 set to indicate the error.
 104 .SH ERRORS
 105 .TP
 106 .B EAGAIN
 107 No signal in
 108 .I set
 109 was delivered within the
 110 .I timeout
 111 period specified to
 112 .BR sigtimedwait ().
 113 .TP
 114 .B EINTR
 115 The wait was interrupted by a signal handler.
 116 (This handler was for a signal other than one of those in
 117 .IR set .)
 118 .TP
 119 .B EINVAL
 120 .I timeout
 121 was invalid.
 122 .SH "CONFORMING TO"
 123 POSIX.1-2001
 124 .SH NOTES
 125 In normal usage, the calling program blocks the signals in
 126 .I set
 127 via a prior call to
 128 .BR sigprocmask (2)
 129 (so that the default disposition for these signals does not occur if they
 130 are delivered between successive calls to
 131 .BR sigwaitinfo ()
 132 or
 133 .BR sigtimedwait ())
 134 and does not establish handlers for these signals.
 135 In a multithreaded program,
 136 the signal should be blocked in all threads to prevent
 137 the signal being delivered to a thread other than the one calling
 138 .BR sigwaitinfo ()
 139 or
 140 .BR sigtimedwait ()).
 141 .PP
 142 POSIX leaves the meaning of a NULL value for the
 143 .I timeout
 144 argument of
 145 .BR sigtimedwait ()
 146 unspecified, permitting the possibility that this has the same meaning
 147 as a call to
 148 .BR sigwaitinfo (),
 149 and indeed this is what is done on Linux.
 150
 151 On Linux,
 152 .BR sigwaitinfo ()
 153 is a library function implemented on top of
 154 .BR sigtimedwait ().
 155 .SH "SEE ALSO"
 156 .BR kill (2),
 157 .BR sigaction (2),
 158 .BR signal (2),
 159 .BR sigpending (2),
 160 .BR sigprocmask (2),
 161 .BR sigqueue (2),
 162 .BR sigsetops (3),
 163 .BR signal (7)