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git://git.code.sf.net/p/cdesktopenv/code
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On SVR4 platforms, select is a sometimes erroneous wrapper around the poll system call, so call poll directly for efficiency purposes if it implies no loss in precision. See, e.g., http://bugs.motifzone.net/long_list.cgi?buglist=129 . src/lib/libast/features/tvlib: - For systems lacking nanosleep, test whether select is truly more precise than poll. src/lib/libast/tm/tvsleep.c: - Verify that tv argument is not null. - Immediately return if asked to sleep for a duration of zero. - Immediately initialize timespec in the nanosleep case. - Revise variable names to use Apps Hungarian. - Use poll instead of select when there is no loss in precision. - Check for overflow in the poll case. - Improve comments. - Revise arithmetic to work with unsigned types, rather than casting to long. - Do not return non-zero if we have slept for a sufficient time.
This commit is contained in:
Lev Kujawski
GitHub
parent
350b52ea4e
commit
4e47f89b06
2 changed files with 121 additions and 45 deletions
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@ -43,6 +43,38 @@ lib utimets link{
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}
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}end
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tst prefer_poll note{ is select less precise than 1 ms }end execute{
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#include <sys/types.h>
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#include <sys/time.h>
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#if _sys_select
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# include <sys/select.h>
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#else
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# include <sys/socket.h>
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#endif
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int
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main()
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{
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struct timeval tvSleep = { 0, 1 }, tvBefore, tvAfter;
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int i;
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/* Take a few measurements to prevent a fluke. */
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for (i = 0; i < 5; ++i)
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{
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gettimeofday(&tvBefore, NULL);
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select(0, NULL, NULL, NULL, &tvSleep);
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gettimeofday(&tvAfter, NULL);
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if (tvAfter.tv_sec == tvBefore.tv_sec + 1)
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{
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--tvAfter.tv_sec;
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tvAfter.tv_usec += 1000000;
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}
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if ((tvAfter.tv_sec == tvBefore.tv_sec) &&
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tvAfter.tv_usec - tvBefore.tv_usec < 1000)
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return -1;
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}
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return 0;
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}
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}end
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tst - -DN=1 - -DN=2 - -DN=3 - -DN=4 output{
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#include <sys/types.h>
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#include <sys/time.h>
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@ -21,14 +21,15 @@
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***********************************************************************/
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#pragma prototyped
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#include <assert.h>
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#include <tv.h>
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#include <tm.h>
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#include <error.h>
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#include "FEATURE/tvlib"
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#if !_lib_nanosleep && !_lib_usleep
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# if _lib_select
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#if !_lib_nanosleep
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# if _lib_select && !_prefer_poll
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# if _sys_select
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# include <sys/select.h>
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# else
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@ -41,7 +42,8 @@
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# endif
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#endif
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#define NANOSECONDS 1000000000L
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#define NANOSECONDS 1000000000L
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#define MILLISECONDS 1000
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/*
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* sleep for tv
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@ -54,16 +56,21 @@
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int
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tvsleep(register const Tv_t* tv, register Tv_t* rv)
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{
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assert(tv); /* Validate argument */
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int r;
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/* Return immediately if asked to sleep for no duration. */
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if (!tv->tv_sec && !tv->tv_nsec)
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return 0;
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{
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#if _lib_nanosleep
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struct timespec stv;
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/* PRECISION: nanoseconds */
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struct timespec stv = { tv->tv_sec, tv->tv_nsec };
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struct timespec srv;
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int r;
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stv.tv_sec = tv->tv_sec;
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stv.tv_nsec = tv->tv_nsec;
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if ((r = nanosleep(&stv, &srv)) && errno == EINTR && rv)
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{
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rv->tv_sec = srv.tv_sec;
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@ -71,20 +78,45 @@ tvsleep(register const Tv_t* tv, register Tv_t* rv)
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}
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return r;
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}
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#else
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Tv_t bv;
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Tv_t tvBefore;
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tvgettime(&bv);
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tvgettime(&tvBefore);
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{
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#if _lib_select
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#if _lib_select && !_prefer_poll
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/* PRECISION: microseconds */
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struct timeval tvSleep = { tv->tv_sec, tv->tv_nsec / 1000 };
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if (tv->tv_nsec % 1000)
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++tvSleep.tv_usec;
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(void)select(0, NiL, NiL, NiL, &tvSleep);
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r = select(0, NiL, NiL, NiL, &tvSleep);
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#elif _lib_poll
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/* PRECISION: milliseconds
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*
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* We can sleep for up to 24 days with a single call to poll
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* on systems with 32-bit integers, so calling sleep first
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* only worsens precision with little gain. For example, the
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* UnixWare manual page for usleep warns that a single call of
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* that function requires eight system calls, but poll only
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* requires one.
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*/
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struct pollfd dummy;
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int timeout = INT_MAX; /* expose bugs */
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if (tv->tv_sec <= (INT_MAX / MILLISECONDS))
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{
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timeout = tv->tv_sec * MILLISECONDS +
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tv->tv_nsec / 1000000;
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if (timeout < INT_MAX && tv->tv_nsec % 1000000)
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++timeout;
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}
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(void)poll(&dummy, 0, timeout);
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#else
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@ -156,59 +188,71 @@ tvsleep(register const Tv_t* tv, register Tv_t* rv)
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}
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}
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#elif _lib_poll
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struct pollfd pfd;
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int t;
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if (!(t = (n + 999999L) / 1000000L))
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t = 1;
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r = poll(&pfd, 0, t);
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#endif
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#endif
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}
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/* Ascertain whether we actually slept for a sufficient time.
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* It is preferable to sleep a little more than necessary than too little.
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/* Unfortunately, some operating systems return success for select
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* or poll without having slept for the specified duration, so check
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* the clock.
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*
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* Although time discrepancies when sleeping are inevitable, tvsleep
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* can guarantee that they always lie on or after the time specified,
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* which is much more useful from the point of view of predictability
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* than if they could also occur before.
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*/
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{
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struct timespec tsAfter;
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long sec, nsec;
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Tv_t tvAfter;
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tvgettime(&tsAfter);
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tvgettime(&tvAfter);
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/* Calculate seconds left to sleep */
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sec = (long)(tv->tv_sec + tv->tv_nsec / NANOSECONDS) -
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((long)tsAfter.tv_sec - (long)bv.tv_sec);
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/* Calculate nanoseconds left to sleep */
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nsec = (long)(tv->tv_nsec % NANOSECONDS) -
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((long)tsAfter.tv_nsec - (long)bv.tv_nsec);
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if (nsec >= NANOSECONDS)
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if (tvAfter.tv_nsec < tvBefore.tv_nsec)
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{
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++sec;
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nsec -= NANOSECONDS;
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if (!tvAfter.tv_sec)
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return 0;
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--tvAfter.tv_sec;
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tvAfter.tv_nsec += (NANOSECONDS - tvBefore.tv_nsec);
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}
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else if (nsec < 0)
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else
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{
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--sec;
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nsec += NANOSECONDS;
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tvAfter.tv_nsec -= tvBefore.tv_nsec;
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}
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if (tvAfter.tv_sec < tvBefore.tv_sec)
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return 0;
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tvAfter.tv_sec -= tvBefore.tv_sec;
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/* tvAfter now holds the non-negative time slept */
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if (sec >= 0 && (sec > 0 || nsec > 0))
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tvBefore = *tv;
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/* Normalize the time to sleep so that ns < 10e9 */
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tvBefore.tv_sec += tvBefore.tv_nsec / NANOSECONDS;
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tvBefore.tv_nsec %= NANOSECONDS;
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if (tvBefore.tv_nsec < tvAfter.tv_nsec)
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{
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if (!tvBefore.tv_sec)
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return 0;
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--tvBefore.tv_sec;
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tvBefore.tv_nsec += (NANOSECONDS - tvAfter.tv_nsec);
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}
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else
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{
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tvBefore.tv_nsec -= tvAfter.tv_nsec;
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}
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if (tvBefore.tv_sec < tvAfter.tv_sec)
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return 0;
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tvBefore.tv_sec -= tvAfter.tv_sec;
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if (tvBefore.tv_sec > 0 || tvBefore.tv_nsec > 0)
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{
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if (rv)
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{
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rv->tv_sec = sec;
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rv->tv_nsec = nsec;
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}
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*rv = tvBefore;
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return -1;
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}
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}
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return r;
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}
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return 0;
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#endif
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