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30 .\" @(#)getitimer.2 8.3 (Berkeley) 5/16/95
31 .\"
32 .Dd April 30, 2010
33 .Dt GETITIMER 2
34 .Os
35 .Sh NAME
36 .Nm getitimer ,
37 .Nm setitimer
38 .Nd get/set value of interval timer
39 .Sh LIBRARY
40 .Lb libc
41 .Sh SYNOPSIS
42 .In sys/time.h
43 .Fd #define ITIMER_REAL 0
44 .Fd #define ITIMER_VIRTUAL 1
45 .Fd #define ITIMER_PROF 2
46 .Ft int
47 .Fn getitimer "int which" "struct itimerval *value"
48 .Ft int
49 .Fn setitimer "int which" "const struct itimerval * restrict value" "struct itimerval * restrict ovalue"
50 .Sh DESCRIPTION
51 The system provides each process with three interval timers,
52 defined in
53 .Ao Pa sys/time.h Ac .
54 The
55 .Fn getitimer
56 call returns the current value for the timer specified in
57 .Fa which
58 in the structure at
59 .Fa value .
60 The
61 .Fn setitimer
62 call sets a timer to the specified
63 .Fa value
64 (returning the previous value of the timer if
65 .Fa ovalue
66 is non-nil).
67 .Pp
68 A timer value is defined by the
69 .Fa itimerval
70 structure:
71 .Bd -literal -offset indent
72 struct itimerval {
73 struct timeval it_interval; /* timer interval */
74 struct timeval it_value; /* current value */
75 };
76 .Ed
77 .Pp
78 If
79 .Fa it_value
80 is non-zero, it indicates the time to the next timer expiration.
81 If
82 .Fa it_interval
83 is non-zero, it specifies a value to be used in reloading
84 .Fa it_value
85 when the timer expires.
86 Setting
87 .Fa it_value
88 to 0 disables a timer.
89 Setting
90 .Fa it_interval
91 to 0 causes a timer to be disabled after its next expiration (assuming
92 .Fa it_value
93 is non-zero).
94 .Pp
95 Time values smaller than the resolution of the
96 system clock are rounded up to this resolution
97 (typically 10 milliseconds).
98 .Pp
99 The
100 .Dv ITIMER_REAL
101 timer decrements in real time.
102 A
103 .Dv SIGALRM
104 signal is
105 delivered when this timer expires.
106 .Pp
107 The
108 .Dv ITIMER_VIRTUAL
109 timer decrements in process virtual time.
110 It runs only when the process is executing.
111 A
112 .Dv SIGVTALRM
113 signal
114 is delivered when it expires.
115 .Pp
116 The
117 .Dv ITIMER_PROF
118 timer decrements both in process virtual time and
119 when the system is running on behalf of the process.
120 It is designed to be used by interpreters in statistically profiling
121 the execution of interpreted programs.
122 Each time the
123 .Dv ITIMER_PROF
124 timer expires, the
125 .Dv SIGPROF
126 signal is
127 delivered.
128 Because this signal may interrupt in-progress
129 system calls, programs using this timer must be prepared to
130 restart interrupted system calls.
131 .Sh NOTES
132 Macros for manipulating time values are defined in the
133 .In sys/time.h
134 header;
135 .Fn timerclear
136 sets a time value to zero,
137 .Fn timerisset
138 tests if a time value is non-zero,
139 .Fn timercmp
140 compares two time values,
141 .Fn timeradd
142 adds a time value to another time value,
143 .Fn timersub
144 computes the time difference between two time values.
145 For additional details, see
146 .Xr timeradd 3 .
147 .Sh RETURN VALUES
148 If the calls succeed, a value of 0 is returned.
149 If an error occurs, the value \-1 is returned, and a more precise error
150 code is placed in the global variable
151 .Va errno .
152 .Sh ERRORS
153 .Fn getitimer
154 and
155 .Fn setitimer
156 will fail if:
157 .Bl -tag -width Er
158 .It Bq Er EFAULT
159 The
160 .Fa value
161 parameter specified a bad address.
162 .It Bq Er EINVAL
163 A
164 .Fa value
165 parameter specified a time that was too large
166 to be handled.
167 .El
168 .Sh SEE ALSO
169 .Xr gettimeofday 2 ,
170 .Xr poll 2 ,
171 .Xr select 2 ,
172 .Xr sigaction 2
173 .Sh STANDARDS
174 The
175 .Fn getitimer
176 and
177 .Fn setitimer
178 functions conform to
179 .St -p1003.1-2001 .
180 The later
181 .St -p1003.1-2008
182 revision however marked both functions as obsolescent,
183 recommending the use of
184 .Xr timer_gettime 2
185 and
186 .Xr timer_settime 2
187 instead.
188 .Sh HISTORY
189 The
190 .Fn getitimer
191 function call appeared in
192 .Bx 4.2 .