r20938: use a double counter trick to avoid the need for atomic increment

diff --git a/source/lib/events/events_signal.c b/source/lib/events/events_signal.c
index 7dd22e89723ae2052bc6d8b0e5df899212315e4a..b6ff3b04ac28991fc0d29ae668c63cd765d7ac17 100644 (file)
--- a/source/lib/events/events_signal.c
+++ b/source/lib/events/events_signal.c
@@ -32,14 +32,24 @@
 /* maximum number of SA_SIGINFO signals to hold in the queue */
 #define SA_INFO_QUEUE_COUNT 10
 
+struct sigcounter {
+       uint32_t count;
+       uint32_t seen;
+};
+
+#define SIG_INCREMENT(s) (s).count++
+#define SIG_SEEN(s, n) (s).seen += (n)
+#define SIG_PENDING(s) ((s).seen != (s).count)
+
+
 /*
   the poor design of signals means that this table must be static global
 */
 static struct {
        struct signal_event *sig_handlers[NUM_SIGNALS];
        struct sigaction oldact[NUM_SIGNALS];
-       uint32_t signal_count[NUM_SIGNALS];
-       uint32_t got_signal;
+       struct sigcounter signal_count[NUM_SIGNALS];
+       struct sigcounter got_signal;
        int pipe_hack[2];
 #ifdef SA_SIGINFO
        /* with SA_SIGINFO we get quite a lot of info per signal */
@@ -47,6 +57,16 @@ static struct {
 #endif
 } sig_state;
 
+/*
+  return number of sigcounter events not processed yet
+*/
+static uint32_t sig_count(struct sigcounter s)
+{
+       if (s.count >= s.seen) {
+               return s.count - s.seen;
+       }
+       return 1 + (0xFFFFFFFF & ~(s.seen - s.count));
+}
 
 /*
   signal handler - redirects to registered signals
@@ -54,8 +74,8 @@ static struct {
 static void signal_handler(int signum)
 {
        char c = 0;
-       sig_state.signal_count[signum]++;
-       sig_state.got_signal++;
+       SIG_INCREMENT(sig_state.signal_count[signum]);
+       SIG_INCREMENT(sig_state.got_signal);
        /* doesn't matter if this pipe overflows */
        write(sig_state.pipe_hack[1], &c, 1);
 }
@@ -66,12 +86,13 @@ static void signal_handler(int signum)
 */
 static void signal_handler_info(int signum, siginfo_t *info, void *uctx)
 {
-       sig_state.sig_info[signum][sig_state.signal_count[signum]] = *info;
+       uint32_t count = sig_count(sig_state.signal_count[signum]);
+       sig_state.sig_info[signum][count] = *info;
 
        signal_handler(signum);
 
        /* handle SA_SIGINFO */
-       if (sig_state.signal_count[signum] == SA_INFO_QUEUE_COUNT) {
+       if (count+1 == SA_INFO_QUEUE_COUNT) {
                /* we've filled the info array - block this signal until
                   these ones are delivered */
                sigset_t set;
@@ -180,13 +201,13 @@ struct signal_event *common_event_add_signal(struct event_context *ev,
 int common_event_check_signal(struct event_context *ev)
 {
        int i;
-       if (sig_state.got_signal == 0) {
+       if (!SIG_PENDING(sig_state.got_signal)) {
                return 0;
        }
        
        for (i=0;i<NUM_SIGNALS+1;i++) {
                struct signal_event *se, *next;
-               uint32_t count = sig_state.signal_count[i];
+               uint32_t count = sig_count(sig_state.signal_count[i]);
 
                if (count == 0) {
                        continue;
@@ -217,8 +238,8 @@ int common_event_check_signal(struct event_context *ev)
                                talloc_free(se);
                        }
                }
-               sig_state.signal_count[i] -= count;
-               sig_state.got_signal -= count;
+               SIG_SEEN(sig_state.signal_count[i], count);
+               SIG_SEEN(sig_state.got_signal, count);
        }
 
        return 1;