Merge in some changes from team/russell/autoservice-nochans-1.4

These changes fix up some dubious code that I came across while auditing what
happens in the autoservice thread when there are no channels currently in
autoservice.

1) Change it so that autoservice thread doesn't keep looping around calling
   ast_waitfor_n() on 0 channels twice a second.  Instead, use a thread condition
   so that the thread properly goes to sleep and does not wake up until a
   channel is put into autoservice.

   This actually fixes an interesting bug, as well.  If the autoservice thread
   is already running (almost always is the case), then when the thread goes
   from having 0 channels to have 1 channel to autoservice, that channel would
   have to wait for up to 1/2 of a second to have the first frame read from it.

2) Fix up the code in ast_waitfor_nandfds() for when it gets called with no
   channels and no fds to poll() on, such as was the case with the previous code
   for the autoservice thread.  In this case, the code would call alloca(0), and
   pass the result as the first argument to poll().  In this case, the 2nd
   argument to poll() specified that there were no fds, so this invalid pointer
   shouldn't actually get dereferenced, but, this code makes it explicit and
   ensures the pointers are NULL unless we have valid data to put there.

(related to issue #12116)


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@105563 65c4cc65-6c06-0410-ace0-fbb531ad65f3

include/asterisk.h

@@ -75,6 +75,7 @@ void dnsmgr_start_refresh(void);		/*!< Provided by dnsmgr.c */
 int dnsmgr_reload(void);			/*!< Provided by dnsmgr.c */
 void threadstorage_init(void);			/*!< Provided by threadstorage.c */
 int astobj2_init(void);				/*! Provided by astobj2.c */
+void ast_autoservice_init(void);    /*!< Provided by autoservice.c */
 
 /* Many headers need 'ast_channel' to be defined */
 struct ast_channel;

main/asterisk.c

@@ -2896,6 +2896,8 @@ int main(int argc, char *argv[])
 
 	astobj2_init();
 
+	ast_autoservice_init();
+
 	if (load_modules(1)) {
 		printf(term_quit());
 		exit(1);

main/autoservice.c

@@ -64,6 +64,7 @@ struct asent {
 };
 
 static AST_LIST_HEAD_STATIC(aslist, asent);
+static ast_cond_t as_cond;
 
 static pthread_t asthread = AST_PTHREADT_NULL;
 
@@ -98,6 +99,9 @@ static void *autoservice_run(void *ign)
 		 * to get used again. */
 		as_chan_list_state++;
 
+		if (AST_LIST_EMPTY(&aslist))
+			ast_cond_wait(&as_cond, &aslist.lock);
+
 		AST_LIST_TRAVERSE(&aslist, as, list) {
 			if (!as->chan->_softhangup) {
 				if (x < MAX_AUTOMONS)
@@ -106,6 +110,7 @@ static void *autoservice_run(void *ign)
 					ast_log(LOG_WARNING, "Exceeded maximum number of automatic monitoring events.  Fix autoservice.c\n");
 			}
 		}
+
 		AST_LIST_UNLOCK(&aslist);
 
 		chan = ast_waitfor_n(mons, x, &ms);
@@ -194,6 +199,8 @@ int ast_autoservice_start(struct ast_channel *chan)
 	ast_channel_unlock(chan);
 
 	AST_LIST_LOCK(&aslist);
+	if (AST_LIST_EMPTY(&aslist))
+		ast_cond_signal(&as_cond);
 	AST_LIST_INSERT_HEAD(&aslist, as, list);
 	AST_LIST_UNLOCK(&aslist);
 
@@ -276,3 +283,8 @@ int ast_autoservice_stop(struct ast_channel *chan)
 
 	return res;
 }
+
+void ast_autoservice_init(void)
+{
+	ast_cond_init(&as_cond, NULL);
+}

main/channel.c

@@ -1616,7 +1616,7 @@ struct ast_channel *ast_waitfor_nandfds(struct ast_channel **c, int n, int *fds,
 	int *exception, int *outfd, int *ms)
 {
 	struct timeval start = { 0 , 0 };
-	struct pollfd *pfds;
+	struct pollfd *pfds = NULL;
 	int res;
 	long rms;
 	int x, y, max;
@@ -1627,11 +1627,12 @@ struct ast_channel *ast_waitfor_nandfds(struct ast_channel **c, int n, int *fds,
 	struct fdmap {
 		int chan;
 		int fdno;
-	} *fdmap;
+	} *fdmap = NULL;
 
-	sz = n * AST_MAX_FDS + nfds;
-	pfds = alloca(sizeof(*pfds) * sz);
-	fdmap = alloca(sizeof(*fdmap) * sz);
+	if ((sz = n * AST_MAX_FDS + nfds)) {
+		pfds = alloca(sizeof(*pfds) * sz);
+		fdmap = alloca(sizeof(*fdmap) * sz);
+	}
 
 	if (outfd)
 		*outfd = -99999;