xref: /freebsd/lib/libc/gen/siginterrupt.3 (revision 8ddb146abcdf061be9f2c0db7e391697dafad85c)
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28.\"     @(#)siginterrupt.3	8.1 (Berkeley) 6/4/93
29.\" $FreeBSD$
30.\"
31.Dd June 4, 1993
32.Dt SIGINTERRUPT 3
33.Os
34.Sh NAME
35.Nm siginterrupt
36.Nd allow signals to interrupt system calls
37.Sh LIBRARY
38.Lb libc
39.Sh SYNOPSIS
40.In signal.h
41.Ft int
42.Fn siginterrupt "int sig" "int flag"
43.Sh DESCRIPTION
44The
45.Fn siginterrupt
46function
47is used to change the system call restart
48behavior when a system call is interrupted by the specified signal.
49If the flag is false (0), then system calls will be restarted if
50they are interrupted by the specified signal
51and no data has been transferred yet.
52System call restart has been the default behavior since
53.Bx 4.2 ,
54and is the default behaviour for
55.Xr signal 3
56on
57.Fx .
58.Pp
59If the flag is true (1),
60then restarting of system calls is disabled.
61If a system call is interrupted by the specified signal
62and no data has been transferred,
63the system call will return \-1 with the global variable
64.Va errno
65set to
66.Er EINTR .
67Interrupted system calls that have started transferring
68data will return the amount of data actually transferred.
69System call interrupt is the signal behavior found on
70.Bx 4.1
71and
72.At V
73systems.
74.Pp
75Note that the new
76.Bx 4.2
77signal handling semantics are not
78altered in any other way.
79Most notably, signal handlers always remain installed until
80explicitly changed by a subsequent
81.Xr sigaction 2
82call, and the signal mask operates as documented in
83.Xr sigaction 2 .
84Programs may switch between restartable and interruptible
85system call operation as often as desired in the execution of a program.
86.Pp
87Issuing a
88.Fn siginterrupt 3
89call during the execution of a signal handler will cause
90the new action to take place on the next signal to be caught.
91.Sh NOTES
92This library routine uses an extension of the
93.Xr sigaction 2
94system call that is not available in
95.Bx 4.2 ,
96hence it should not be used if backward compatibility is needed.
97.Sh RETURN VALUES
98.Rv -std siginterrupt
99.Sh ERRORS
100The
101.Fn siginterrupt
102call fails if:
103.Bl -tag -width Er
104.It Bq Er EINVAL
105The
106.Fa sig
107argument
108is not a valid signal number.
109.El
110.Sh SEE ALSO
111.Xr sigaction 2 ,
112.Xr sigprocmask 2 ,
113.Xr sigsuspend 2 ,
114.Xr signal 3
115.Sh HISTORY
116The
117.Fn siginterrupt
118function appeared in
119.Bx 4.3 .
120