thread*.c: waiting on sigwait_fd performs periodic ubf wakeups

We need to be able to perform periodic ubf_list wakeups when a
thread is sleeping and waiting on signals.

[ruby-core:88088] [Misc #14937] [Bug #5343]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@64115 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 54 insertions, 17 deletions

diff --git a/thread.c b/thread.c
index 75d31cfb7a..161f16365c 100644
--- a/thread.c
+++ b/thread.c
@@ -110,8 +110,8 @@ static int timespec_cmp(const struct timespec *a, const struct timespec *b);
 static int timespec_update_expire(struct timespec *, const struct timespec *);
 static void getclockofday(struct timespec *);
 NORETURN(static void async_bug_fd(const char *mesg, int errno_arg, int fd));
-static void consume_communication_pipe(int fd);
-static void check_signals_nogvl(rb_thread_t *, int sigwait_fd);
+static int consume_communication_pipe(int fd);
+static int check_signals_nogvl(rb_thread_t *, int sigwait_fd);
 void rb_sigwait_fd_migrate(rb_vm_t *); /* process.c */
 
 #define eKillSignal INT2FIX(0)
@@ -385,6 +385,15 @@ ubf_sigwait(void *ignore)
 #error "unsupported thread type"
 #endif
 
+/*
+ * TODO: somebody with win32 knowledge should be able to get rid of
+ * timer-thread by busy-waiting on signals.  And it should be possible
+ * to make the GVL in thread_pthread.c be platform-independent.
+ */
+#ifndef BUSY_WAIT_SIGNALS
+#  define BUSY_WAIT_SIGNALS (0)
+#endif
+
 #if THREAD_DEBUG
 static int debug_mutex_initialized = 1;
 static rb_nativethread_lock_t debug_mutex;
@@ -2173,7 +2182,7 @@ rb_threadptr_execute_interrupts(rb_thread_t *th, int blocking_timing)
 	    int sigwait_fd = rb_sigwait_fd_get(th);
 
 	    if (sigwait_fd >= 0) {
-		consume_communication_pipe(sigwait_fd);
+		(void)consume_communication_pipe(sigwait_fd);
 		ruby_sigchld_handler(th->vm);
 		rb_sigwait_fd_put(th, sigwait_fd);
 		rb_sigwait_fd_migrate(th->vm);
@@ -3885,6 +3894,21 @@ select_set_free(VALUE p)
     return Qfalse;
 }
 
+static const struct timespec *
+sigwait_timeout(rb_thread_t *th, int sigwait_fd, const struct timespec *orig,
+                int *drained_p)
+{
+    static const struct timespec quantum = { 0, TIME_QUANTUM_USEC * 1000 };
+
+    if (sigwait_fd >= 0 && (!ubf_threads_empty() || BUSY_WAIT_SIGNALS)) {
+        *drained_p = check_signals_nogvl(th, sigwait_fd);
+        if (!orig || timespec_cmp(orig, &quantum) > 0)
+            return &quantum;
+    }
+
+    return orig;
+}
+
 static VALUE
 do_select(VALUE p)
 {
@@ -3892,6 +3916,8 @@ do_select(VALUE p)
     int MAYBE_UNUSED(result);
     int lerrno;
     struct timespec ts, end, *tsp;
+    const struct timespec *to;
+    struct timeval tv;
 
     timeout_prepare(&tsp, &ts, &end, set->timeout);
 #define restore_fdset(dst, src) \
@@ -3903,17 +3929,20 @@ do_select(VALUE p)
      TRUE)
 
     do {
+	int drained;
 	lerrno = 0;
 
 	BLOCKING_REGION(set->th, {
+	    to = sigwait_timeout(set->th, set->sigwait_fd, tsp, &drained);
 	    result = native_fd_select(set->max, set->rset, set->wset, set->eset,
-				      timeval_for(set->timeout, tsp), set->th);
+				      timeval_for(&tv, to), set->th);
 	    if (result < 0) lerrno = errno;
 	}, set->sigwait_fd >= 0 ? ubf_sigwait : ubf_select, set->th, FALSE);
 
-        if (set->sigwait_fd >= 0 && rb_fd_isset(set->sigwait_fd, set->rset)) {
-            result--;
-            check_signals_nogvl(set->th, set->sigwait_fd);
+        if (set->sigwait_fd >= 0) {
+            if (result > 0 && rb_fd_isset(set->sigwait_fd, set->rset))
+                result--;
+            (void)check_signals_nogvl(set->th, set->sigwait_fd);
         }
 
         RUBY_VM_CHECK_INTS_BLOCKING(set->th->ec); /* may raise */
@@ -4042,6 +4071,8 @@ rb_wait_for_single_fd(int fd, int events, struct timeval *timeout)
     struct pollfd fds[2];
     int result = 0, lerrno;
     struct timespec ts, end, *tsp;
+    const struct timespec *to;
+    int drained;
     rb_thread_t *th = GET_THREAD();
     nfds_t nfds;
     rb_unblock_function_t *ubf;
@@ -4066,16 +4097,17 @@ rb_wait_for_single_fd(int fd, int events, struct timeval *timeout)
 
         lerrno = 0;
         BLOCKING_REGION(th, {
-            result = ppoll(fds, nfds, tsp, NULL);
+            to = sigwait_timeout(th, fds[1].fd, tsp, &drained);
+            result = ppoll(fds, nfds, to, NULL);
             if (result < 0) lerrno = errno;
         }, ubf, th, FALSE);
 
         if (fds[1].fd >= 0) {
-            if (fds[1].revents) {
+            if (result > 0 && fds[1].revents) {
                 result--;
-                check_signals_nogvl(th, fds[1].fd);
                 fds[1].revents = 0;
             }
+            (void)check_signals_nogvl(th, fds[1].fd);
             rb_sigwait_fd_put(th, fds[1].fd);
             rb_sigwait_fd_migrate(th->vm);
         }
@@ -4228,18 +4260,22 @@ async_bug_fd(const char *mesg, int errno_arg, int fd)
 }
 
 /* VM-dependent API is not available for this function */
-static void
+static int
 consume_communication_pipe(int fd)
 {
 #define CCP_READ_BUFF_SIZE 1024
     /* buffer can be shared because no one refers to them. */
     static char buff[CCP_READ_BUFF_SIZE];
     ssize_t result;
+    int ret = FALSE; /* for rb_sigwait_sleep */
 
     while (1) {
 	result = read(fd, buff, sizeof(buff));
-	if (result == 0) {
-	    return;
+	if (result > 0) {
+	    ret = TRUE;
+	}
+	else if (result == 0) {
+	    return ret;
 	}
 	else if (result < 0) {
 	    int e = errno;
@@ -4250,7 +4286,7 @@ consume_communication_pipe(int fd)
 #if defined(EWOULDBLOCK) && EWOULDBLOCK != EAGAIN
 	      case EWOULDBLOCK:
 #endif
-		return;
+		return ret;
 	      default:
 		async_bug_fd("consume_communication_pipe: read", e, fd);
 	    }
@@ -4258,12 +4294,11 @@ consume_communication_pipe(int fd)
     }
 }
 
-static void
+static int
 check_signals_nogvl(rb_thread_t *th, int sigwait_fd)
 {
     rb_vm_t *vm = GET_VM(); /* th may be 0 */
-
-    consume_communication_pipe(sigwait_fd);
+    int ret = consume_communication_pipe(sigwait_fd);
     ubf_wakeup_all_threads();
     ruby_sigchld_handler(vm);
     if (rb_signal_buff_size()) {
@@ -4272,7 +4307,9 @@ check_signals_nogvl(rb_thread_t *th, int sigwait_fd)
             RUBY_VM_SET_TRAP_INTERRUPT(th->ec);
         else
             threadptr_trap_interrupt(vm->main_thread);
+        ret = TRUE; /* for SIGCHLD_LOSSY && rb_sigwait_sleep */
     }
+    return ret;
 }
 
 void