From a837a3820985a078834cb6bd9b754572a5c2e4ee Mon Sep 17 00:00:00 2001 From: Ben Pfaff Date: Tue, 12 Aug 2008 14:41:48 -0700 Subject: [PATCH] Implement signal-driven time tracking. Checking the current time only when a periodic timer expires allows us to reduce the number of system calls to obtain the current time to 10 per second (from an arbitrary number) plus one per poll loop. This fixes poll_block() to properly handle being interrupted. Otherwise, a timeout longer than the interval between signals will never complete (because it will restart from the beginning after every signal). --- include/timeval.h | 16 ++++ lib/Makefile.am | 1 + lib/poll-loop.c | 7 +- lib/timeval.c | 229 ++++++++++++++++++++++++++++++++++++++++++++++ 4 files changed, 249 insertions(+), 4 deletions(-) create mode 100644 lib/timeval.c diff --git a/include/timeval.h b/include/timeval.h index 6a30f973..b31cac11 100644 --- a/include/timeval.h +++ b/include/timeval.h @@ -34,9 +34,12 @@ #ifndef TIMEVAL_H #define TIMEVAL_H 1 +#include #include "type-props.h" #include "util.h" +struct pollfd; + /* POSIX allows floating-point time_t, but we don't support it. */ BUILD_ASSERT_DECL(TYPE_IS_INTEGER(time_t)); @@ -47,4 +50,17 @@ BUILD_ASSERT_DECL(TYPE_IS_SIGNED(time_t)); #define TIME_MAX TYPE_MAXIMUM(time_t) #define TIME_MIN TYPE_MINIMUM(time_t) +/* Interval between updates to the time reported by time_gettimeofday(), in ms. + * This should not be adjusted much below 10 ms or so with the current + * implementation, or too much time will be wasted in signal handlers and calls + * to time(0). */ +#define TIME_UPDATE_INTERVAL 100 + +void time_init(void); +void time_refresh(void); +time_t time_now(void); +long long int time_msec(void); +void time_alarm(unsigned int secs); +int time_poll(struct pollfd *, int n_pollfds, int timeout); + #endif /* timeval.h */ diff --git a/lib/Makefile.am b/lib/Makefile.am index 3d2a4ef7..6c02909f 100644 --- a/lib/Makefile.am +++ b/lib/Makefile.am @@ -24,6 +24,7 @@ libopenflow_a_SOURCES = \ random.c \ rconn.c \ socket-util.c \ + timeval.c \ util.c \ vconn-tcp.c \ vconn-unix.c \ diff --git a/lib/poll-loop.c b/lib/poll-loop.c index 71f1e6f2..6bf05ddd 100644 --- a/lib/poll-loop.c +++ b/lib/poll-loop.c @@ -39,6 +39,7 @@ #include #include #include "list.h" +#include "timeval.h" #define THIS_MODULE VLM_poll_loop #include "vlog.h" @@ -143,11 +144,9 @@ poll_block(void) n_pollfds++; } - do { - retval = poll(pollfds, n_pollfds, timeout); - } while (retval < 0 && errno == EINTR); + retval = time_poll(pollfds, n_pollfds, timeout); if (retval < 0) { - VLOG_ERR("poll: %s", strerror(errno)); + VLOG_ERR("poll: %s", strerror(-retval)); } for (node = waiters.next; node != &waiters; ) { diff --git a/lib/timeval.c b/lib/timeval.c new file mode 100644 index 00000000..3fb83200 --- /dev/null +++ b/lib/timeval.c @@ -0,0 +1,229 @@ +/* Copyright (c) 2008 The Board of Trustees of The Leland Stanford + * Junior University + * + * We are making the OpenFlow specification and associated documentation + * (Software) available for public use and benefit with the expectation + * that others will use, modify and enhance the Software and contribute + * those enhancements back to the community. However, since we would + * like to make the Software available for broadest use, with as few + * restrictions as possible permission is hereby granted, free of + * charge, to any person obtaining a copy of this Software to deal in + * the Software under the copyrights without restriction, including + * without limitation the rights to use, copy, modify, merge, publish, + * distribute, sublicense, and/or sell copies of the Software, and to + * permit persons to whom the Software is furnished to do so, subject to + * the following conditions: + * + * The above copyright notice and this permission notice shall be + * included in all copies or substantial portions of the Software. + * + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, + * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF + * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND + * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS + * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN + * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN + * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE + * SOFTWARE. + * + * The name and trademarks of copyright holder(s) may NOT be used in + * advertising or publicity pertaining to the Software or any + * derivatives without specific, written prior permission. + */ + +#include +#include "timeval.h" +#include +#include +#include +#include +#include +#include +#include "fatal-signal.h" +#include "util.h" + +/* Initialized? */ +static bool inited; + +/* Has a timer tick occurred? */ +static volatile sig_atomic_t tick; + +/* The current time, as of the last refresh. */ +static struct timeval now; + +/* Time at which to die with SIGALRM (if not TIME_MIN). */ +static time_t deadline = TIME_MIN; + +static void sigalrm_handler(int); +static void refresh_if_ticked(void); +static time_t time_add(time_t, time_t); +static void block_sigalrm(sigset_t *); +static void unblock_sigalrm(const sigset_t *); + +/* Initializes the timetracking module. */ +void +time_init(void) +{ + struct sigaction sa; + struct itimerval itimer; + + if (inited) { + return; + } + + inited = true; + gettimeofday(&now, NULL); + tick = false; + + /* Set up signal handler. */ + memset(&sa, 0, sizeof sa); + sa.sa_handler = sigalrm_handler; + sigemptyset(&sa.sa_mask); + sa.sa_flags = SA_RESTART; + if (sigaction(SIGALRM, &sa, NULL)) { + fatal(errno, "sigaction(SIGALRM) failed"); + } + + /* Set up periodic timer. */ + itimer.it_interval.tv_sec = 0; + itimer.it_interval.tv_usec = TIME_UPDATE_INTERVAL * 1000; + itimer.it_value = itimer.it_interval; + if (setitimer(ITIMER_REAL, &itimer, NULL)) { + fatal(errno, "setitimer failed"); + } +} + +/* Forces a refresh of the current time from the kernel. It is not usually + * necessary to call this function, since the time will be refreshed + * automatically at least every TIME_UPDATE_INTERVAL milliseconds. */ +void +time_refresh(void) +{ + gettimeofday(&now, NULL); + tick = false; +} + +/* Returns the current time, in seconds. */ +time_t +time_now(void) +{ + refresh_if_ticked(); + return now.tv_sec; +} + +/* Returns the current time, in ms (within TIME_UPDATE_INTERVAL ms). */ +long long int +time_msec(void) +{ + refresh_if_ticked(); + return (long long int) now.tv_sec * 1000 + now.tv_usec / 1000; +} + +/* Configures the program to die with SIGALRM 'secs' seconds from now, if + * 'secs' is nonzero, or disables the feature if 'secs' is zero. */ +void +time_alarm(unsigned int secs) +{ + sigset_t oldsigs; + + time_init(); + block_sigalrm(&oldsigs); + deadline = secs ? time_add(time_now(), secs) : TIME_MIN; + unblock_sigalrm(&oldsigs); +} + +/* Like poll(), except: + * + * - On error, returns a negative error code (instead of setting errno). + * + * - If interrupted by a signal, retries automatically until the original + * 'timeout' expires. (Because of this property, this function will + * never return -EINTR.) + * + * - As a side effect, refreshes the current time (like time_refresh()). + */ +int +time_poll(struct pollfd *pollfds, int n_pollfds, int timeout) +{ + long long int start; + sigset_t oldsigs; + bool blocked; + int retval; + + time_refresh(); + start = time_msec(); + blocked = false; + for (;;) { + int time_left; + if (timeout > 0) { + long long int elapsed = time_msec() - start; + time_left = timeout >= elapsed ? timeout - elapsed : 0; + } else { + time_left = timeout; + } + + retval = poll(pollfds, n_pollfds, time_left); + if (retval < 0) { + retval = -errno; + } + if (retval != -EINTR) { + break; + } + + if (!blocked && deadline == TIME_MIN) { + block_sigalrm(&oldsigs); + blocked = true; + } + time_refresh(); + } + if (blocked) { + unblock_sigalrm(&oldsigs); + } + return retval; +} + +/* Returns the sum of 'a' and 'b', with saturation on overflow or underflow. */ +static time_t +time_add(time_t a, time_t b) +{ + return (a >= 0 + ? (b > TIME_MAX - a ? TIME_MAX : a + b) + : (b < TIME_MIN - a ? TIME_MIN : a + b)); +} + +static void +sigalrm_handler(int sig_nr) +{ + tick = true; + if (deadline != TIME_MIN && time(0) > deadline) { + fatal_signal_handler(sig_nr); + } +} + +static void +refresh_if_ticked(void) +{ + assert(inited); + if (tick) { + time_refresh(); + } +} + +static void +block_sigalrm(sigset_t *oldsigs) +{ + sigset_t sigalrm; + sigemptyset(&sigalrm); + sigaddset(&sigalrm, SIGALRM); + if (sigprocmask(SIG_BLOCK, &sigalrm, oldsigs)) { + fatal(errno, "sigprocmask"); + } +} + +static void +unblock_sigalrm(const sigset_t *oldsigs) +{ + if (sigprocmask(SIG_SETMASK, oldsigs, NULL)) { + fatal(errno, "sigprocmask"); + } +} -- 2.30.2