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28 .\" @(#)siginterrupt.3 8.1 (Berkeley) 6/4/93

29 .\" $FreeBSD: src/lib/libc/gen/siginterrupt.3,v 1.15 2007/01/09 00:27:55 imp Exp $

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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

44 The

45 .Fn siginterrupt

46 function

47 is used to change the system call restart

48 behavior when a system call is interrupted by the specified signal.

49 If the flag is false (0), then system calls will be restarted if

50 they are interrupted by the specified signal

51 and no data has been transferred yet.

52 System call restart has been the default behavior since

53 .Bx 4.2 ,

54 and is the default behaviour for

55 .Xr signal 3

56 on

57 .Fx .

58 .Pp

59 If the flag is true (1),

60 then restarting of system calls is disabled.

61 If a system call is interrupted by the specified signal

62 and no data has been transferred,

63 the system call will return \-1 with the global variable

64 .Va errno

65 set to

66 .Er EINTR .

67 Interrupted system calls that have started transferring

68 data will return the amount of data actually transferred.

69 System call interrupt is the signal behavior found on

70 .Bx 4.1

71 and

72 .At V

73 systems.

74 .Pp

75 Note that the new

76 .Bx 4.2

77 signal handling semantics are not

78 altered in any other way.

79 Most notably, signal handlers always remain installed until

80 explicitly changed by a subsequent

81 .Xr sigaction 2

82 call, and the signal mask operates as documented in

83 .Xr sigaction 2 .

84 Programs may switch between restartable and interruptible

85 system call operation as often as desired in the execution of a program.

86 .Pp

87 Issuing a

88 .Fn siginterrupt 3

89 call during the execution of a signal handler will cause

90 the new action to take place on the next signal to be caught.

91 .Sh NOTES

92 This library routine uses an extension of the

93 .Xr sigaction 2

94 system call that is not available in

95 .Bx 4.2 ;

96 hence, it should not be used if backward compatibility is needed.

97 .Sh RETURN VALUES

98 .Rv -std siginterrupt

99 .Sh ERRORS

100 The

101 .Fn siginterrupt

102 call fails if:

103 .Bl -tag -width Er

104 .It Bq Er EINVAL

105 The

106 .Fa sig

107 argument

108 is not a valid signal number.

109 .El

110 .Sh SEE ALSO

111 .Xr sigaction 2 ,

112 .Xr sigblock 2 ,

113 .Xr sigpause 2 ,

114 .Xr sigsetmask 2 ,

115 .Xr signal 3

116 .Sh HISTORY

117 The

118 .Fn siginterrupt

119 function appeared in

120 .Bx 4.3 .