fixes #530 POSIX pollqs should scale horizontally (epoll)

This should help Linux platforms scale even further with NNG.

Port events and *maybe* poll are the last to do.  Probably select
will remain left in the cold, because honestly select based systems
are already performance constrained.

src/platform/posix/posix_pollq_epoll.c

@@ -40,19 +40,21 @@ typedef struct nni_posix_pollq {
 	int      epfd;  // epoll handle
 	int      evfd;  // event fd (to wake us for other stuff)
 	bool     close; // request for worker to exit
-	nni_thr  thr;   // worker thread
+	bool     init;
+	nni_thr  thr; // worker thread
 	nni_list reapq;
 } nni_posix_pollq;
 
 // single global instance for now.
-static nni_posix_pollq nni_posix_global_pollq;
+static nni_posix_pollq *nni_epoll_pqs;
+static int              nni_epoll_npq;
 
 void
 nni_posix_pfd_init(nni_posix_pfd *pfd, int fd, nni_posix_pfd_cb cb, void *arg)
 {
 	nni_posix_pollq *pq;
 
-	pq = &nni_posix_global_pollq;
+	pq = &nni_epoll_pqs[fd % nni_epoll_npq];
 
 	(void) fcntl(fd, F_SETFD, FD_CLOEXEC);
 	(void) fcntl(fd, F_SETFL, O_NONBLOCK);
@@ -191,7 +193,7 @@ nni_posix_pollq_reap(nni_posix_pollq *pq)
 }
 
 static void
-nni_posix_poll_thr(void *arg)
+nni_epoll_thr(void *arg)
 {
 	nni_posix_pollq   *pq = arg;
 	struct epoll_event events[NNI_MAX_EPOLL_EVENTS];
@@ -245,30 +247,32 @@ nni_posix_poll_thr(void *arg)
 }
 
 static void
-nni_posix_pollq_destroy(nni_posix_pollq *pq)
+nni_epoll_pq_destroy(nni_posix_pollq *pq)
 {
 	uint64_t one = 1;
 
-	nni_mtx_lock(&pq->mtx);
-	pq->close = true;
+	if (pq->init) {
+		nni_mtx_lock(&pq->mtx);
+		pq->close = true;
 
-	if (write(pq->evfd, &one, sizeof(one)) != sizeof(one)) {
-		// This should never occur, and if it does it could
-		// lead to a hang.
-		nni_panic("BUG! unable to write to evfd!");
-	}
-	nni_mtx_unlock(&pq->mtx);
+		if (write(pq->evfd, &one, sizeof(one)) != sizeof(one)) {
+			// This should never occur, and if it does it could
+			// lead to a hang.
+			nni_panic("BUG! unable to write to evfd!");
+		}
+		nni_mtx_unlock(&pq->mtx);
 
-	nni_thr_fini(&pq->thr);
+		nni_thr_fini(&pq->thr);
 
-	close(pq->evfd);
-	close(pq->epfd);
+		close(pq->evfd);
+		close(pq->epfd);
 
-	nni_mtx_fini(&pq->mtx);
+		nni_mtx_fini(&pq->mtx);
+	}
 }
 
 static int
-nni_posix_pollq_add_eventfd(nni_posix_pollq *pq)
+nni_epoll_pq_add_eventfd(nni_posix_pollq *pq)
 {
 	// add event fd so we can wake ourself on exit
 	struct epoll_event ev;
@@ -295,10 +299,16 @@ nni_posix_pollq_add_eventfd(nni_posix_pollq *pq)
 }
 
 static int
-nni_posix_pollq_create(nni_posix_pollq *pq)
+nni_epoll_pq_create(nni_posix_pollq *pq)
 {
 	int rv;
 
+	NNI_LIST_INIT(&pq->reapq, nni_posix_pfd, node);
+	nni_mtx_init(&pq->mtx);
+	nni_cv_init(&pq->cv, &pq->mtx);
+	pq->epfd = -1;
+	pq->init = true;
+
 #if NNG_HAVE_EPOLL_CREATE1
 	if ((pq->epfd = epoll_create1(EPOLL_CLOEXEC)) < 0) {
 		return (nni_plat_errno(errno));
@@ -314,16 +324,12 @@ nni_posix_pollq_create(nni_posix_pollq *pq)
 
 	pq->close = false;
 
-	NNI_LIST_INIT(&pq->reapq, nni_posix_pfd, node);
-	nni_mtx_init(&pq->mtx);
-	nni_cv_init(&pq->cv, &pq->mtx);
-
-	if ((rv = nni_posix_pollq_add_eventfd(pq)) != 0) {
+	if ((rv = nni_epoll_pq_add_eventfd(pq)) != 0) {
 		(void) close(pq->epfd);
 		nni_mtx_fini(&pq->mtx);
 		return (rv);
 	}
-	if ((rv = nni_thr_init(&pq->thr, nni_posix_poll_thr, pq)) != 0) {
+	if ((rv = nni_thr_init(&pq->thr, nni_epoll_thr, pq)) != 0) {
 		(void) close(pq->epfd);
 		(void) close(pq->evfd);
 		nni_mtx_fini(&pq->mtx);
@@ -337,14 +343,46 @@ nni_posix_pollq_create(nni_posix_pollq *pq)
 int
 nni_posix_pollq_sysinit(nng_init_params *params)
 {
-	NNI_ARG_UNUSED(params);
-	return (nni_posix_pollq_create(&nni_posix_global_pollq));
+	int16_t num_thr;
+	int16_t max_thr;
+
+	max_thr = params->max_poller_threads;
+	num_thr = params->num_poller_threads;
+
+	if ((max_thr > 0) && (num_thr > max_thr)) {
+		num_thr = max_thr;
+	}
+	if (num_thr < 1) {
+		num_thr = 1;
+	}
+	params->num_poller_threads = num_thr;
+	if ((nni_epoll_pqs = NNI_ALLOC_STRUCTS(nni_epoll_pqs, num_thr)) ==
+	    NULL) {
+		return (NNG_ENOMEM);
+	}
+
+	nni_epoll_npq = num_thr;
+	for (int i = 0; i < num_thr; i++) {
+		int rv;
+		if ((rv = nni_epoll_pq_create(&nni_epoll_pqs[i])) != 0) {
+			nni_posix_pollq_sysfini();
+			return (rv);
+		}
+	}
+	return (0);
 }
 
 void
 nni_posix_pollq_sysfini(void)
 {
-	nni_posix_pollq_destroy(&nni_posix_global_pollq);
+	if (nni_epoll_npq > 0) {
+		for (int i = 0; i < nni_epoll_npq; i++) {
+			nni_epoll_pq_destroy(&nni_epoll_pqs[i]);
+		}
+		NNI_FREE_STRUCTS(nni_epoll_pqs, nni_epoll_npq);
+		nni_epoll_pqs = NULL;
+		nni_epoll_npq = 0;
+	}
 }
 
 #endif // NNG_HAVE_EPOLL