Add isc_helper API that adds 1:1 thread for each loop

Add an extra thread that can be used to offload operations that would
affect latency, but are not long-running tasks; those are handled by
isc_work API.

Each isc_loop now has matching isc_helper thread that also built on top
of uv_loop.  In fact, it matches most of the isc_loop functionality, but
only the `isc_helper_run()` asynchronous call is exposed.

lib/isc/Makefile.am

@@ -31,6 +31,7 @@ libisc_la_HEADERS =			\
 	include/isc/hash.h		\
 	include/isc/hashmap.h		\
 	include/isc/heap.h		\
+	include/isc/helper.h		\
 	include/isc/hex.h		\
 	include/isc/histo.h		\
 	include/isc/hmac.h		\
@@ -135,6 +136,7 @@ libisc_la_SOURCES =		\
 	hash.c			\
 	hashmap.c		\
 	heap.c			\
+	helper.c		\
 	hex.c			\
 	histo.c			\
 	hmac.c			\

lib/isc/helper.c

@@ -0,0 +1,68 @@
+/*
+ * Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+ *
+ * SPDX-License-Identifier: MPL-2.0
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, you can obtain one at https://mozilla.org/MPL/2.0/.
+ *
+ * See the COPYRIGHT file distributed with this work for additional
+ * information regarding copyright ownership.
+ */
+
+#include <stdlib.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <isc/atomic.h>
+#include <isc/barrier.h>
+#include <isc/condition.h>
+#include <isc/helper.h>
+#include <isc/job.h>
+#include <isc/loop.h>
+#include <isc/magic.h>
+#include <isc/mem.h>
+#include <isc/mutex.h>
+#include <isc/refcount.h>
+#include <isc/result.h>
+#include <isc/signal.h>
+#include <isc/strerr.h>
+#include <isc/thread.h>
+#include <isc/util.h>
+#include <isc/uv.h>
+#include <isc/work.h>
+
+#include "async_p.h"
+#include "job_p.h"
+#include "loop_p.h"
+
+void
+isc_helper_run(isc_loop_t *loop, isc_job_cb cb, void *cbarg) {
+	REQUIRE(VALID_LOOP(loop));
+	REQUIRE(cb != NULL);
+
+	isc_loop_t *helper = &loop->loopmgr->helpers[loop->tid];
+
+	isc_job_t *job = isc_mem_get(helper->mctx, sizeof(*job));
+	*job = (isc_job_t){
+		.cb = cb,
+		.cbarg = cbarg,
+	};
+
+	cds_wfcq_node_init(&job->wfcq_node);
+
+	/*
+	 * cds_wfcq_enqueue() is non-blocking and enqueues the job to async
+	 * queue.
+	 *
+	 * The function returns 'false' in case the queue was empty - in such
+	 * case we need to trigger the async callback.
+	 */
+	if (!cds_wfcq_enqueue(&helper->async_jobs.head,
+			      &helper->async_jobs.tail, &job->wfcq_node))
+	{
+		int r = uv_async_send(&helper->async_trigger);
+		UV_RUNTIME_CHECK(uv_async_send, r);
+	}
+}

lib/isc/include/isc/helper.h

@@ -0,0 +1,45 @@
+/*
+ * Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+ *
+ * SPDX-License-Identifier: MPL-2.0
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, you can obtain one at https://mozilla.org/MPL/2.0/.
+ *
+ * See the COPYRIGHT file distributed with this work for additional
+ * information regarding copyright ownership.
+ */
+
+/*! \file isc/helper.h */
+
+#pragma once
+
+#include <inttypes.h>
+
+#include <isc/job.h>
+#include <isc/lang.h>
+#include <isc/loop.h>
+#include <isc/mem.h>
+#include <isc/types.h>
+
+ISC_LANG_BEGINDECLS
+
+void
+isc_helper_run(isc_loop_t *loop, isc_job_cb cb, void *cbarg);
+/*%<
+ * Schedule the job callback 'cb' to be run on the 'loop' event loop.
+ *
+ * Requires:
+ *
+ *\li	'loop' is a valid isc event loop
+ *\li	'cb' is a callback function, must be non-NULL
+ *\li	'cbarg' is passed to the 'cb' as the only argument, may be NULL
+ */
+
+#define isc_helper_current(cb, cbarg) isc_async_run(isc_loop(), cb, cbarg)
+/*%<
+ * Helper macro to run the job on the current loop
+ */
+
+ISC_LANG_ENDDECLS

lib/isc/loop.c

@@ -186,7 +186,8 @@ shutdown_cb(uv_async_t *handle) {
 }
 
 static void
-loop_init(isc_loop_t *loop, isc_loopmgr_t *loopmgr, uint32_t tid) {
+loop_init(isc_loop_t *loop, isc_loopmgr_t *loopmgr, uint32_t tid,
+	  const char *kind) {
 	*loop = (isc_loop_t){
 		.tid = tid,
 		.loopmgr = loopmgr,
@@ -225,7 +226,7 @@ loop_init(isc_loop_t *loop, isc_loopmgr_t *loopmgr, uint32_t tid) {
 	uv_handle_set_data(&loop->quiescent, loop);
 
 	char name[16];
-	snprintf(name, sizeof(name), "loop-%08" PRIx32, tid);
+	snprintf(name, sizeof(name), "%s-%08" PRIx32, kind, tid);
 	isc_mem_create(&loop->mctx);
 	isc_mem_setname(loop->mctx, name);
 
@@ -249,6 +250,16 @@ quiescent_cb(uv_prepare_t *handle) {
 #endif
 }
 
+static void
+helper_close(isc_loop_t *loop) {
+	int r = uv_loop_close(&loop->loop);
+	UV_RUNTIME_CHECK(uv_loop_close, r);
+
+	INSIST(cds_wfcq_empty(&loop->async_jobs.head, &loop->async_jobs.tail));
+
+	isc_mem_detach(&loop->mctx);
+}
+
 static void
 loop_close(isc_loop_t *loop) {
 	int r = uv_loop_close(&loop->loop);
@@ -262,9 +273,32 @@ loop_close(isc_loop_t *loop) {
 	isc_mem_detach(&loop->mctx);
 }
 
+static void *
+helper_thread(void *arg) {
+	isc_loop_t *helper = (isc_loop_t *)arg;
+
+	int r = uv_prepare_start(&helper->quiescent, quiescent_cb);
+	UV_RUNTIME_CHECK(uv_prepare_start, r);
+
+	isc_barrier_wait(&helper->loopmgr->starting);
+
+	r = uv_run(&helper->loop, UV_RUN_DEFAULT);
+	UV_RUNTIME_CHECK(uv_run, r);
+
+	/* Invalidate the helper early */
+	helper->magic = 0;
+
+	isc_barrier_wait(&helper->loopmgr->stopping);
+
+	return (NULL);
+}
+
 static void *
 loop_thread(void *arg) {
 	isc_loop_t *loop = (isc_loop_t *)arg;
+	isc_loopmgr_t *loopmgr = loop->loopmgr;
+	isc_loop_t *helper = &loopmgr->helpers[loop->tid];
+	char name[32];
 	/* Initialize the thread_local variables*/
 
 	REQUIRE(isc__loop_local == NULL || isc__loop_local == loop);
@@ -272,10 +306,15 @@ loop_thread(void *arg) {
 
 	isc__tid_init(loop->tid);
 
+	/* Start the helper thread */
+	isc_thread_create(helper_thread, helper, &helper->thread);
+	snprintf(name, sizeof(name), "isc-helper-%04" PRIu32, loop->tid);
+	isc_thread_setname(helper->thread, name);
+
 	int r = uv_prepare_start(&loop->quiescent, quiescent_cb);
 	UV_RUNTIME_CHECK(uv_prepare_start, r);
 
-	isc_barrier_wait(&loop->loopmgr->starting);
+	isc_barrier_wait(&loopmgr->starting);
 
 	enum cds_wfcq_ret ret = __cds_wfcq_splice_blocking(
 		&loop->async_jobs.head, &loop->async_jobs.tail,
@@ -293,7 +332,11 @@ loop_thread(void *arg) {
 	/* Invalidate the loop early */
 	loop->magic = 0;
 
-	isc_barrier_wait(&loop->loopmgr->stopping);
+	/* Shutdown the helper thread */
+	r = uv_async_send(&helper->shutdown_trigger);
+	UV_RUNTIME_CHECK(uv_async_send, r);
+
+	isc_barrier_wait(&loopmgr->stopping);
 
 	return (NULL);
 }
@@ -342,16 +385,24 @@ isc_loopmgr_create(isc_mem_t *mctx, uint32_t nloops, isc_loopmgr_t **loopmgrp) {
 
 	isc_mem_attach(mctx, &loopmgr->mctx);
 
-	isc_barrier_init(&loopmgr->pausing, loopmgr->nloops);
+	/* We need to double the number for loops and helpers */
-	isc_barrier_init(&loopmgr->resuming, loopmgr->nloops);
+	isc_barrier_init(&loopmgr->pausing, loopmgr->nloops * 2);
-	isc_barrier_init(&loopmgr->starting, loopmgr->nloops);
+	isc_barrier_init(&loopmgr->resuming, loopmgr->nloops * 2);
-	isc_barrier_init(&loopmgr->stopping, loopmgr->nloops);
+	isc_barrier_init(&loopmgr->starting, loopmgr->nloops * 2);
+	isc_barrier_init(&loopmgr->stopping, loopmgr->nloops * 2);
 
 	loopmgr->loops = isc_mem_cget(loopmgr->mctx, loopmgr->nloops,
 				      sizeof(loopmgr->loops[0]));
 	for (size_t i = 0; i < loopmgr->nloops; i++) {
 		isc_loop_t *loop = &loopmgr->loops[i];
-		loop_init(loop, loopmgr, i);
+		loop_init(loop, loopmgr, i, "loop");
+	}
+
+	loopmgr->helpers = isc_mem_cget(loopmgr->mctx, loopmgr->nloops,
+					sizeof(loopmgr->helpers[0]));
+	for (size_t i = 0; i < loopmgr->nloops; i++) {
+		isc_loop_t *loop = &loopmgr->helpers[i];
+		loop_init(loop, loopmgr, i, "helper");
 	}
 
 	loopmgr->sigint = isc_signal_new(loopmgr, isc__loopmgr_signal, loopmgr,
@@ -465,6 +516,7 @@ isc_loopmgr_run(isc_loopmgr_t *loopmgr) {
 void
 isc_loopmgr_pause(isc_loopmgr_t *loopmgr) {
 	REQUIRE(VALID_LOOPMGR(loopmgr));
+	REQUIRE(isc_tid() != ISC_TID_UNKNOWN);
 
 	if (isc_log_wouldlog(ISC_LOG_DEBUG(1))) {
 		isc_log_write(ISC_LOGCATEGORY_GENERAL, ISC_LOGMODULE_OTHER,
@@ -472,6 +524,13 @@ isc_loopmgr_pause(isc_loopmgr_t *loopmgr) {
 			      "loop exclusive mode: starting");
 	}
 
+	for (size_t i = 0; i < loopmgr->nloops; i++) {
+		isc_loop_t *helper = &loopmgr->helpers[i];
+
+		int r = uv_async_send(&helper->pause_trigger);
+		UV_RUNTIME_CHECK(uv_async_send, r);
+	}
+
 	for (size_t i = 0; i < loopmgr->nloops; i++) {
 		isc_loop_t *loop = &loopmgr->loops[i];
 
@@ -526,6 +585,12 @@ isc_loopmgr_destroy(isc_loopmgr_t **loopmgrp) {
 	RUNTIME_CHECK(atomic_compare_exchange_strong(&loopmgr->running,
 						     &(bool){ true }, false));
 
+	/* Wait for all helpers to finish */
+	for (size_t i = 0; i < loopmgr->nloops; i++) {
+		isc_loop_t *helper = &loopmgr->helpers[i];
+		isc_thread_join(helper->thread, NULL);
+	}
+
 	/* First wait for all loops to finish */
 	for (size_t i = 1; i < loopmgr->nloops; i++) {
 		isc_loop_t *loop = &loopmgr->loops[i];
@@ -534,6 +599,13 @@ isc_loopmgr_destroy(isc_loopmgr_t **loopmgrp) {
 
 	loopmgr->magic = 0;
 
+	for (size_t i = 0; i < loopmgr->nloops; i++) {
+		isc_loop_t *helper = &loopmgr->helpers[i];
+		helper_close(helper);
+	}
+	isc_mem_cput(loopmgr->mctx, loopmgr->helpers, loopmgr->nloops,
+		     sizeof(loopmgr->helpers[0]));
+
 	for (size_t i = 0; i < loopmgr->nloops; i++) {
 		isc_loop_t *loop = &loopmgr->loops[i];
 		loop_close(loop);

lib/isc/loop_p.h

@@ -110,6 +110,7 @@ struct isc_loopmgr {
 
 	/* per-thread objects */
 	isc_loop_t *loops;
+	isc_loop_t *helpers;
 };
 
 /*