1 /* -----------------------------------------------------------------------------
2 * $Id: Select.c,v 1.4 1999/11/03 15:04:25 simonmar Exp $
4 * (c) The GHC Team 1995-1999
6 * Support for concurrent non-blocking I/O and thread waiting.
8 * ---------------------------------------------------------------------------*/
10 /* we're outside the realms of POSIX here... */
11 #define NON_POSIX_SOURCE
20 # if defined(HAVE_SYS_TYPES_H)
21 # include <sys/types.h>
24 # ifdef HAVE_SYS_TIME_H
25 # include <sys/time.h>
28 nat ticks_since_select = 0;
30 /* Argument 'wait' says whether to wait for I/O to become available,
31 * or whether to just check and return immediately. If there are
32 * other threads ready to run, we normally do the non-waiting variety,
33 * otherwise we wait (see Schedule.c).
35 * SMP note: must be called with sched_mutex locked.
38 awaitEvent(rtsBool wait)
40 #ifdef mingw32_TARGET_OS
42 * Win32 doesn't support select(). ToDo: use MsgWaitForMultipleObjects()
43 * to achieve (similar) effect.
49 StgTSO *tso, *prev, *next;
52 int min, numFound, delta;
56 #ifndef linux_TARGET_OS
57 struct timeval tv_before,tv_after;
60 IF_DEBUG(scheduler,belch("Checking for threads blocked on I/O...\n"));
62 /* see how long it's been since we last checked the blocked queue.
63 * ToDo: make this check atomic, so we don't lose any ticks.
65 delta = ticks_since_select;
66 ticks_since_select = 0;
67 delta = delta * TICK_MILLISECS * 1000;
69 min = wait == rtsTrue ? 0x7fffffff : 0;
72 * Collect all of the fd's that we're interested in, and capture
73 * the minimum waiting time (in microseconds) for the delayed threads.
78 for(tso = blocked_queue_hd; tso != END_TSO_QUEUE; tso = next) {
81 switch (tso->why_blocked) {
84 int fd = tso->block_info.fd;
85 maxfd = (fd > maxfd) ? fd : maxfd;
92 int fd = tso->block_info.fd;
93 maxfd = (fd > maxfd) ? fd : maxfd;
100 if ((int)tso->block_info.delay < min)
101 min = tso->block_info.delay;
110 /* Release the scheduler lock while we do the poll.
111 * this means that someone might muck with the blocked_queue
112 * while we do this, but it shouldn't matter:
114 * - another task might poll for I/O and remove one
115 * or more threads from the blocked_queue.
116 * - more I/O threads may be added to blocked_queue.
117 * - more delayed threads may be added to blocked_queue. We'll
118 * just subtract delta from their delays after the poll.
120 * I believe none of these cases lead to trouble --SDM.
122 RELEASE_LOCK(&sched_mutex);
124 /* Check for any interesting events */
126 tv.tv_sec = min / 1000000;
127 tv.tv_usec = min % 1000000;
129 #ifndef linux_TARGET_OS
130 gettimeofday(&tv_before, (struct timezone *) NULL);
133 while ((numFound = select(maxfd+1, &rfd, &wfd, NULL, &tv)) < 0) {
134 if (errno != EINTR) {
135 /* fflush(stdout); */
136 fprintf(stderr, "awaitEvent: select failed\n");
137 stg_exit(EXIT_FAILURE);
139 ACQUIRE_LOCK(&sched_mutex);
140 /* We got a signal; could be one of ours. If so, we need
141 * to start up the signal handler straight away, otherwise
142 * we could block for a long time before the signal is
145 if (signals_pending()) {
146 start_signal_handlers();
150 /* If new runnable threads have arrived, stop waiting for
153 if (run_queue_hd != END_TSO_QUEUE) {
156 RELEASE_LOCK(&sched_mutex);
161 File descriptors ready, but we don't know how much time was spent
162 in the select(). To interpolate, we compare the time before
163 and after the select().
166 #ifdef linux_TARGET_OS
167 /* on Linux, tv is set to indicate the amount of time not
168 * slept, so we don't need to gettimeofday() to find out.
170 delta += min - (tv.tv_sec * 1000000 + tv.tv_usec);
172 gettimeofday(&tv_after, (struct timezone *) NULL);
173 delta += (tv_after.tv_sec - tv_before.tv_sec) * 1000000 +
174 tv_after.tv_usec - tv_before.tv_usec;
180 ACQUIRE_LOCK(&sched_mutex);
183 Step through the waiting queue, unblocking every thread that now has
184 a file descriptor in a ready state.
186 For the delayed threads, decrement the number of microsecs
187 we've been blocked for. Unblock the threads that have thusly expired.
191 for(tso = blocked_queue_hd; tso != END_TSO_QUEUE; tso = next) {
193 switch (tso->why_blocked) {
195 ready = FD_ISSET(tso->block_info.fd, &rfd);
199 ready = FD_ISSET(tso->block_info.fd, &wfd);
203 tso->block_info.delay -= delta;
204 ready = (tso->block_info.delay <= 0);
212 IF_DEBUG(scheduler,belch("Waking up thread %d\n", tso->id));
213 tso->why_blocked = NotBlocked;
214 tso->link = END_TSO_QUEUE;
215 PUSH_ON_RUN_QUEUE(tso);
218 blocked_queue_hd = tso;
226 blocked_queue_hd = blocked_queue_tl = END_TSO_QUEUE;
228 prev->link = END_TSO_QUEUE;
229 blocked_queue_tl = prev;