Adding upstream version 1:9.18.19.upstream/1%9.18.19upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1368 insertions, 0 deletions

diff --git a/lib/isc/task.c b/lib/isc/task.c
new file mode 100644
index 0000000..439d430
--- /dev/null
+++ b/lib/isc/task.c
@@ -0,0 +1,1368 @@
+/*
+ * 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 */
+
+/*
+ * XXXRTH  Need to document the states a task can be in, and the rules
+ * for changing states.
+ */
+
+#include <stdbool.h>
+#include <unistd.h>
+
+#include <isc/app.h>
+#include <isc/atomic.h>
+#include <isc/condition.h>
+#include <isc/event.h>
+#include <isc/log.h>
+#include <isc/magic.h>
+#include <isc/mem.h>
+#include <isc/once.h>
+#include <isc/print.h>
+#include <isc/random.h>
+#include <isc/refcount.h>
+#include <isc/string.h>
+#include <isc/task.h>
+#include <isc/thread.h>
+#include <isc/time.h>
+#include <isc/util.h>
+
+#ifdef HAVE_LIBXML2
+#include <libxml/xmlwriter.h>
+#define ISC_XMLCHAR (const xmlChar *)
+#endif /* HAVE_LIBXML2 */
+
+#ifdef HAVE_JSON_C
+#include <json_object.h>
+#endif /* HAVE_JSON_C */
+
+#include "task_p.h"
+
+/*
+ * Task manager is built around 'as little locking as possible' concept.
+ * Each thread has his own queue of tasks to be run, if a task is in running
+ * state it will stay on the runner it's currently on, if a task is in idle
+ * state it can be woken up on a specific runner with isc_task_sendto - that
+ * helps with data locality on CPU.
+ *
+ * To make load even some tasks (from task pools) are bound to specific
+ * queues using isc_task_create_bound. This way load balancing between
+ * CPUs/queues happens on the higher layer.
+ */
+
+#ifdef ISC_TASK_TRACE
+#define XTRACE(m) \
+	fprintf(stderr, "task %p thread %zu: %s\n", task, isc_tid_v, (m))
+#define XTTRACE(t, m) \
+	fprintf(stderr, "task %p thread %zu: %s\n", (t), isc_tid_v, (m))
+#define XTHREADTRACE(m) fprintf(stderr, "thread %zu: %s\n", isc_tid_v, (m))
+#else /* ifdef ISC_TASK_TRACE */
+#define XTRACE(m)
+#define XTTRACE(t, m)
+#define XTHREADTRACE(m)
+#endif /* ifdef ISC_TASK_TRACE */
+
+/***
+ *** Types.
+ ***/
+
+typedef enum {
+	task_state_idle,    /* not doing anything, events queue empty */
+	task_state_ready,   /* waiting in worker's queue */
+	task_state_running, /* actively processing events */
+	task_state_done	    /* shutting down, no events or references */
+} task_state_t;
+
+#if defined(HAVE_LIBXML2) || defined(HAVE_JSON_C)
+static const char *statenames[] = {
+	"idle",
+	"ready",
+	"running",
+	"done",
+};
+#endif /* if defined(HAVE_LIBXML2) || defined(HAVE_JSON_C) */
+
+#define TASK_MAGIC    ISC_MAGIC('T', 'A', 'S', 'K')
+#define VALID_TASK(t) ISC_MAGIC_VALID(t, TASK_MAGIC)
+
+struct isc_task {
+	/* Not locked. */
+	unsigned int magic;
+	isc_taskmgr_t *manager;
+	isc_mutex_t lock;
+	/* Locked by task lock. */
+	int threadid;
+	task_state_t state;
+	isc_refcount_t references;
+	isc_refcount_t running;
+	isc_eventlist_t events;
+	isc_eventlist_t on_shutdown;
+	unsigned int nevents;
+	unsigned int quantum;
+	isc_stdtime_t now;
+	isc_time_t tnow;
+	char name[16];
+	void *tag;
+	bool bound;
+	/* Protected by atomics */
+	atomic_bool shuttingdown;
+	atomic_bool privileged;
+	/* Locked by task manager lock. */
+	LINK(isc_task_t) link;
+};
+
+#define TASK_SHUTTINGDOWN(t) (atomic_load_acquire(&(t)->shuttingdown))
+#define TASK_PRIVILEGED(t)   (atomic_load_acquire(&(t)->privileged))
+
+#define TASK_MANAGER_MAGIC ISC_MAGIC('T', 'S', 'K', 'M')
+#define VALID_MANAGER(m)   ISC_MAGIC_VALID(m, TASK_MANAGER_MAGIC)
+
+struct isc_taskmgr {
+	/* Not locked. */
+	unsigned int magic;
+	isc_refcount_t references;
+	isc_mem_t *mctx;
+	isc_mutex_t lock;
+	atomic_uint_fast32_t tasks_count;
+	isc_nm_t *netmgr;
+
+	/* Locked by task manager lock. */
+	unsigned int default_quantum;
+	LIST(isc_task_t) tasks;
+	atomic_uint_fast32_t mode;
+	atomic_bool exclusive_req;
+	bool exiting;
+	isc_task_t *excl;
+};
+
+#define DEFAULT_DEFAULT_QUANTUM 25
+
+/*%
+ * The following are intended for internal use (indicated by "isc__"
+ * prefix) but are not declared as static, allowing direct access from
+ * unit tests etc.
+ */
+
+bool
+isc_task_purgeevent(isc_task_t *task, isc_event_t *event);
+void
+isc_taskmgr_setexcltask(isc_taskmgr_t *mgr, isc_task_t *task);
+isc_result_t
+isc_taskmgr_excltask(isc_taskmgr_t *mgr, isc_task_t **taskp);
+
+/***
+ *** Tasks.
+ ***/
+
+static void
+task_finished(isc_task_t *task) {
+	isc_taskmgr_t *manager = task->manager;
+	isc_mem_t *mctx = manager->mctx;
+	REQUIRE(EMPTY(task->events));
+	REQUIRE(task->nevents == 0);
+	REQUIRE(EMPTY(task->on_shutdown));
+	REQUIRE(task->state == task_state_done);
+
+	XTRACE("task_finished");
+
+	isc_refcount_destroy(&task->running);
+	isc_refcount_destroy(&task->references);
+
+	LOCK(&manager->lock);
+	UNLINK(manager->tasks, task, link);
+	atomic_fetch_sub(&manager->tasks_count, 1);
+	UNLOCK(&manager->lock);
+
+	isc_mutex_destroy(&task->lock);
+	task->magic = 0;
+	isc_mem_put(mctx, task, sizeof(*task));
+
+	isc_taskmgr_detach(&manager);
+}
+
+isc_result_t
+isc_task_create(isc_taskmgr_t *manager, unsigned int quantum,
+		isc_task_t **taskp) {
+	return (isc_task_create_bound(manager, quantum, taskp, -1));
+}
+
+isc_result_t
+isc_task_create_bound(isc_taskmgr_t *manager, unsigned int quantum,
+		      isc_task_t **taskp, int threadid) {
+	isc_task_t *task = NULL;
+	bool exiting;
+
+	REQUIRE(VALID_MANAGER(manager));
+	REQUIRE(taskp != NULL && *taskp == NULL);
+
+	XTRACE("isc_task_create");
+
+	task = isc_mem_get(manager->mctx, sizeof(*task));
+	*task = (isc_task_t){ 0 };
+
+	isc_taskmgr_attach(manager, &task->manager);
+
+	if (threadid == -1) {
+		/*
+		 * Task is not pinned to a queue, it's threadid will be
+		 * chosen when first task will be sent to it - either
+		 * randomly or specified by isc_task_sendto.
+		 */
+		task->bound = false;
+		task->threadid = -1;
+	} else {
+		/*
+		 * Task is pinned to a queue, it'll always be run
+		 * by a specific thread.
+		 */
+		task->bound = true;
+		task->threadid = threadid;
+	}
+
+	isc_mutex_init(&task->lock);
+	task->state = task_state_idle;
+
+	isc_refcount_init(&task->references, 1);
+	isc_refcount_init(&task->running, 0);
+	INIT_LIST(task->events);
+	INIT_LIST(task->on_shutdown);
+	task->nevents = 0;
+	task->quantum = (quantum > 0) ? quantum : manager->default_quantum;
+	atomic_init(&task->shuttingdown, false);
+	atomic_init(&task->privileged, false);
+	task->now = 0;
+	isc_time_settoepoch(&task->tnow);
+	memset(task->name, 0, sizeof(task->name));
+	task->tag = NULL;
+	INIT_LINK(task, link);
+	task->magic = TASK_MAGIC;
+
+	LOCK(&manager->lock);
+	exiting = manager->exiting;
+	if (!exiting) {
+		APPEND(manager->tasks, task, link);
+		atomic_fetch_add(&manager->tasks_count, 1);
+	}
+	UNLOCK(&manager->lock);
+
+	if (exiting) {
+		isc_refcount_destroy(&task->running);
+		isc_refcount_decrement(&task->references);
+		isc_refcount_destroy(&task->references);
+		isc_mutex_destroy(&task->lock);
+		isc_taskmgr_detach(&task->manager);
+		isc_mem_put(manager->mctx, task, sizeof(*task));
+		return (ISC_R_SHUTTINGDOWN);
+	}
+
+	*taskp = task;
+
+	return (ISC_R_SUCCESS);
+}
+
+void
+isc_task_attach(isc_task_t *source, isc_task_t **targetp) {
+	/*
+	 * Attach *targetp to source.
+	 */
+
+	REQUIRE(VALID_TASK(source));
+	REQUIRE(targetp != NULL && *targetp == NULL);
+
+	XTTRACE(source, "isc_task_attach");
+
+	isc_refcount_increment(&source->references);
+
+	*targetp = source;
+}
+
+static bool
+task_shutdown(isc_task_t *task) {
+	bool was_idle = false;
+	isc_event_t *event, *prev;
+
+	/*
+	 * Caller must be holding the task's lock.
+	 */
+
+	XTRACE("task_shutdown");
+
+	if (atomic_compare_exchange_strong(&task->shuttingdown,
+					   &(bool){ false }, true))
+	{
+		XTRACE("shutting down");
+		if (task->state == task_state_idle) {
+			INSIST(EMPTY(task->events));
+			task->state = task_state_ready;
+			was_idle = true;
+		}
+		INSIST(task->state == task_state_ready ||
+		       task->state == task_state_running);
+
+		/*
+		 * Note that we post shutdown events LIFO.
+		 */
+		for (event = TAIL(task->on_shutdown); event != NULL;
+		     event = prev)
+		{
+			prev = PREV(event, ev_link);
+			DEQUEUE(task->on_shutdown, event, ev_link);
+			ENQUEUE(task->events, event, ev_link);
+			task->nevents++;
+		}
+	}
+
+	return (was_idle);
+}
+
+/*
+ * Moves a task onto the appropriate run queue.
+ *
+ * Caller must NOT hold queue lock.
+ */
+static void
+task_ready(isc_task_t *task) {
+	isc_taskmgr_t *manager = task->manager;
+	REQUIRE(VALID_MANAGER(manager));
+
+	XTRACE("task_ready");
+
+	isc_refcount_increment0(&task->running);
+	LOCK(&task->lock);
+	isc_nm_task_enqueue(manager->netmgr, task, task->threadid);
+	UNLOCK(&task->lock);
+}
+
+void
+isc_task_ready(isc_task_t *task) {
+	task_ready(task);
+}
+
+static bool
+task_detach(isc_task_t *task) {
+	/*
+	 * Caller must be holding the task lock.
+	 */
+
+	XTRACE("detach");
+
+	if (isc_refcount_decrement(&task->references) == 1 &&
+	    task->state == task_state_idle)
+	{
+		INSIST(EMPTY(task->events));
+		/*
+		 * There are no references to this task, and no
+		 * pending events.  We could try to optimize and
+		 * either initiate shutdown or clean up the task,
+		 * depending on its state, but it's easier to just
+		 * make the task ready and allow run() or the event
+		 * loop to deal with shutting down and termination.
+		 */
+		task->state = task_state_ready;
+		return (true);
+	}
+
+	return (false);
+}
+
+void
+isc_task_detach(isc_task_t **taskp) {
+	isc_task_t *task;
+	bool was_idle;
+
+	/*
+	 * Detach *taskp from its task.
+	 */
+
+	REQUIRE(taskp != NULL);
+	task = *taskp;
+	REQUIRE(VALID_TASK(task));
+
+	XTRACE("isc_task_detach");
+
+	LOCK(&task->lock);
+	was_idle = task_detach(task);
+	UNLOCK(&task->lock);
+
+	if (was_idle) {
+		task_ready(task);
+	}
+
+	*taskp = NULL;
+}
+
+static bool
+task_send(isc_task_t *task, isc_event_t **eventp, int c) {
+	bool was_idle = false;
+	isc_event_t *event;
+
+	/*
+	 * Caller must be holding the task lock.
+	 */
+
+	REQUIRE(eventp != NULL);
+	event = *eventp;
+	*eventp = NULL;
+	REQUIRE(event != NULL);
+	REQUIRE(event->ev_type > 0);
+	REQUIRE(task->state != task_state_done);
+	REQUIRE(!ISC_LINK_LINKED(event, ev_ratelink));
+
+	XTRACE("task_send");
+
+	if (task->bound) {
+		c = task->threadid;
+	} else if (c < 0) {
+		c = -1;
+	}
+
+	if (task->state == task_state_idle) {
+		was_idle = true;
+		task->threadid = c;
+		INSIST(EMPTY(task->events));
+		task->state = task_state_ready;
+	}
+	INSIST(task->state == task_state_ready ||
+	       task->state == task_state_running);
+	ENQUEUE(task->events, event, ev_link);
+	task->nevents++;
+
+	return (was_idle);
+}
+
+void
+isc_task_send(isc_task_t *task, isc_event_t **eventp) {
+	isc_task_sendto(task, eventp, -1);
+}
+
+void
+isc_task_sendanddetach(isc_task_t **taskp, isc_event_t **eventp) {
+	isc_task_sendtoanddetach(taskp, eventp, -1);
+}
+
+void
+isc_task_sendto(isc_task_t *task, isc_event_t **eventp, int c) {
+	bool was_idle;
+
+	/*
+	 * Send '*event' to 'task'.
+	 */
+
+	REQUIRE(VALID_TASK(task));
+	XTRACE("isc_task_send");
+
+	/*
+	 * We're trying hard to hold locks for as short a time as possible.
+	 * We're also trying to hold as few locks as possible.  This is why
+	 * some processing is deferred until after the lock is released.
+	 */
+	LOCK(&task->lock);
+	was_idle = task_send(task, eventp, c);
+	UNLOCK(&task->lock);
+
+	if (was_idle) {
+		/*
+		 * We need to add this task to the ready queue.
+		 *
+		 * We've waited until now to do it because making a task
+		 * ready requires locking the manager.  If we tried to do
+		 * this while holding the task lock, we could deadlock.
+		 *
+		 * We've changed the state to ready, so no one else will
+		 * be trying to add this task to the ready queue.  The
+		 * only way to leave the ready state is by executing the
+		 * task.  It thus doesn't matter if events are added,
+		 * removed, or a shutdown is started in the interval
+		 * between the time we released the task lock, and the time
+		 * we add the task to the ready queue.
+		 */
+		task_ready(task);
+	}
+}
+
+void
+isc_task_sendtoanddetach(isc_task_t **taskp, isc_event_t **eventp, int c) {
+	bool idle1, idle2;
+	isc_task_t *task;
+
+	/*
+	 * Send '*event' to '*taskp' and then detach '*taskp' from its
+	 * task.
+	 */
+
+	REQUIRE(taskp != NULL);
+	task = *taskp;
+	REQUIRE(VALID_TASK(task));
+	XTRACE("isc_task_sendanddetach");
+
+	LOCK(&task->lock);
+	idle1 = task_send(task, eventp, c);
+	idle2 = task_detach(task);
+	UNLOCK(&task->lock);
+
+	/*
+	 * If idle1, then idle2 shouldn't be true as well since we're holding
+	 * the task lock, and thus the task cannot switch from ready back to
+	 * idle.
+	 */
+	INSIST(!(idle1 && idle2));
+
+	if (idle1 || idle2) {
+		task_ready(task);
+	}
+
+	*taskp = NULL;
+}
+
+#define PURGE_OK(event) (((event)->ev_attributes & ISC_EVENTATTR_NOPURGE) == 0)
+
+static unsigned int
+dequeue_events(isc_task_t *task, void *sender, isc_eventtype_t first,
+	       isc_eventtype_t last, void *tag, isc_eventlist_t *events,
+	       bool purging) {
+	isc_event_t *event, *next_event;
+	unsigned int count = 0;
+
+	REQUIRE(VALID_TASK(task));
+	REQUIRE(last >= first);
+
+	XTRACE("dequeue_events");
+
+	/*
+	 * Events matching 'sender', whose type is >= first and <= last, and
+	 * whose tag is 'tag' will be dequeued.  If 'purging', matching events
+	 * which are marked as unpurgable will not be dequeued.
+	 *
+	 * sender == NULL means "any sender", and tag == NULL means "any tag".
+	 */
+
+	LOCK(&task->lock);
+
+	for (event = HEAD(task->events); event != NULL; event = next_event) {
+		next_event = NEXT(event, ev_link);
+		if (event->ev_type >= first && event->ev_type <= last &&
+		    (sender == NULL || event->ev_sender == sender) &&
+		    (tag == NULL || event->ev_tag == tag) &&
+		    (!purging || PURGE_OK(event)))
+		{
+			DEQUEUE(task->events, event, ev_link);
+			task->nevents--;
+			ENQUEUE(*events, event, ev_link);
+			count++;
+		}
+	}
+
+	UNLOCK(&task->lock);
+
+	return (count);
+}
+
+unsigned int
+isc_task_purgerange(isc_task_t *task, void *sender, isc_eventtype_t first,
+		    isc_eventtype_t last, void *tag) {
+	unsigned int count;
+	isc_eventlist_t events;
+	isc_event_t *event, *next_event;
+	REQUIRE(VALID_TASK(task));
+
+	/*
+	 * Purge events from a task's event queue.
+	 */
+
+	XTRACE("isc_task_purgerange");
+
+	ISC_LIST_INIT(events);
+
+	count = dequeue_events(task, sender, first, last, tag, &events, true);
+
+	for (event = HEAD(events); event != NULL; event = next_event) {
+		next_event = NEXT(event, ev_link);
+		ISC_LIST_UNLINK(events, event, ev_link);
+		isc_event_free(&event);
+	}
+
+	/*
+	 * Note that purging never changes the state of the task.
+	 */
+
+	return (count);
+}
+
+unsigned int
+isc_task_purge(isc_task_t *task, void *sender, isc_eventtype_t type,
+	       void *tag) {
+	/*
+	 * Purge events from a task's event queue.
+	 */
+	REQUIRE(VALID_TASK(task));
+
+	XTRACE("isc_task_purge");
+
+	return (isc_task_purgerange(task, sender, type, type, tag));
+}
+
+bool
+isc_task_purgeevent(isc_task_t *task, isc_event_t *event) {
+	bool found = false;
+
+	/*
+	 * Purge 'event' from a task's event queue.
+	 */
+
+	REQUIRE(VALID_TASK(task));
+
+	/*
+	 * If 'event' is on the task's event queue, it will be purged,
+	 * unless it is marked as unpurgeable.  'event' does not have to be
+	 * on the task's event queue; in fact, it can even be an invalid
+	 * pointer.  Purging only occurs if the event is actually on the task's
+	 * event queue.
+	 *
+	 * Purging never changes the state of the task.
+	 */
+
+	LOCK(&task->lock);
+	if (ISC_LINK_LINKED(event, ev_link)) {
+		DEQUEUE(task->events, event, ev_link);
+		task->nevents--;
+		found = true;
+	}
+	UNLOCK(&task->lock);
+
+	if (!found) {
+		return (false);
+	}
+
+	isc_event_free(&event);
+
+	return (true);
+}
+
+unsigned int
+isc_task_unsend(isc_task_t *task, void *sender, isc_eventtype_t type, void *tag,
+		isc_eventlist_t *events) {
+	/*
+	 * Remove events from a task's event queue.
+	 */
+
+	XTRACE("isc_task_unsend");
+
+	return (dequeue_events(task, sender, type, type, tag, events, false));
+}
+
+isc_result_t
+isc_task_onshutdown(isc_task_t *task, isc_taskaction_t action, void *arg) {
+	bool disallowed = false;
+	isc_result_t result = ISC_R_SUCCESS;
+	isc_event_t *event;
+
+	/*
+	 * Send a shutdown event with action 'action' and argument 'arg' when
+	 * 'task' is shutdown.
+	 */
+
+	REQUIRE(VALID_TASK(task));
+	REQUIRE(action != NULL);
+
+	event = isc_event_allocate(task->manager->mctx, NULL,
+				   ISC_TASKEVENT_SHUTDOWN, action, arg,
+				   sizeof(*event));
+
+	if (TASK_SHUTTINGDOWN(task)) {
+		disallowed = true;
+		result = ISC_R_SHUTTINGDOWN;
+	} else {
+		LOCK(&task->lock);
+		ENQUEUE(task->on_shutdown, event, ev_link);
+		UNLOCK(&task->lock);
+	}
+
+	if (disallowed) {
+		isc_mem_put(task->manager->mctx, event, sizeof(*event));
+	}
+
+	return (result);
+}
+
+void
+isc_task_shutdown(isc_task_t *task) {
+	bool was_idle;
+
+	/*
+	 * Shutdown 'task'.
+	 */
+
+	REQUIRE(VALID_TASK(task));
+
+	LOCK(&task->lock);
+	was_idle = task_shutdown(task);
+	UNLOCK(&task->lock);
+
+	if (was_idle) {
+		task_ready(task);
+	}
+}
+
+void
+isc_task_destroy(isc_task_t **taskp) {
+	/*
+	 * Destroy '*taskp'.
+	 */
+
+	REQUIRE(taskp != NULL);
+
+	isc_task_shutdown(*taskp);
+	isc_task_detach(taskp);
+}
+
+void
+isc_task_setname(isc_task_t *task, const char *name, void *tag) {
+	/*
+	 * Name 'task'.
+	 */
+
+	REQUIRE(VALID_TASK(task));
+
+	LOCK(&task->lock);
+	strlcpy(task->name, name, sizeof(task->name));
+	task->tag = tag;
+	UNLOCK(&task->lock);
+}
+
+const char *
+isc_task_getname(isc_task_t *task) {
+	REQUIRE(VALID_TASK(task));
+
+	return (task->name);
+}
+
+void *
+isc_task_gettag(isc_task_t *task) {
+	REQUIRE(VALID_TASK(task));
+
+	return (task->tag);
+}
+
+isc_nm_t *
+isc_task_getnetmgr(isc_task_t *task) {
+	REQUIRE(VALID_TASK(task));
+
+	return (task->manager->netmgr);
+}
+
+void
+isc_task_setquantum(isc_task_t *task, unsigned int quantum) {
+	REQUIRE(VALID_TASK(task));
+
+	LOCK(&task->lock);
+	task->quantum = (quantum > 0) ? quantum
+				      : task->manager->default_quantum;
+	UNLOCK(&task->lock);
+}
+
+/***
+ *** Task Manager.
+ ***/
+
+static isc_result_t
+task_run(isc_task_t *task) {
+	unsigned int dispatch_count = 0;
+	bool finished = false;
+	isc_event_t *event = NULL;
+	isc_result_t result = ISC_R_SUCCESS;
+	uint32_t quantum;
+
+	REQUIRE(VALID_TASK(task));
+
+	LOCK(&task->lock);
+	quantum = task->quantum;
+
+	if (task->state != task_state_ready) {
+		goto done;
+	}
+
+	INSIST(task->state == task_state_ready);
+	task->state = task_state_running;
+	XTRACE("running");
+	XTRACE(task->name);
+	TIME_NOW(&task->tnow);
+	task->now = isc_time_seconds(&task->tnow);
+
+	while (true) {
+		if (!EMPTY(task->events)) {
+			event = HEAD(task->events);
+			DEQUEUE(task->events, event, ev_link);
+			task->nevents--;
+
+			/*
+			 * Execute the event action.
+			 */
+			XTRACE("execute action");
+			XTRACE(task->name);
+			if (event->ev_action != NULL) {
+				UNLOCK(&task->lock);
+				(event->ev_action)(task, event);
+				LOCK(&task->lock);
+			}
+			XTRACE("execution complete");
+			dispatch_count++;
+		}
+
+		if (isc_refcount_current(&task->references) == 0 &&
+		    EMPTY(task->events) && !TASK_SHUTTINGDOWN(task))
+		{
+			/*
+			 * There are no references and no pending events for
+			 * this task, which means it will not become runnable
+			 * again via an external action (such as sending an
+			 * event or detaching).
+			 *
+			 * We initiate shutdown to prevent it from becoming a
+			 * zombie.
+			 *
+			 * We do this here instead of in the "if
+			 * EMPTY(task->events)" block below because:
+			 *
+			 *	If we post no shutdown events, we want the task
+			 *	to finish.
+			 *
+			 *	If we did post shutdown events, will still want
+			 *	the task's quantum to be applied.
+			 */
+			INSIST(!task_shutdown(task));
+		}
+
+		if (EMPTY(task->events)) {
+			/*
+			 * Nothing else to do for this task right now.
+			 */
+			XTRACE("empty");
+			if (isc_refcount_current(&task->references) == 0 &&
+			    TASK_SHUTTINGDOWN(task))
+			{
+				/*
+				 * The task is done.
+				 */
+				XTRACE("done");
+				task->state = task_state_done;
+			} else if (task->state == task_state_running) {
+				XTRACE("idling");
+				task->state = task_state_idle;
+			}
+			break;
+		} else if (dispatch_count >= quantum) {
+			/*
+			 * Our quantum has expired, but there is more work to be
+			 * done.  We'll requeue it to the ready queue later.
+			 *
+			 * We don't check quantum until dispatching at least one
+			 * event, so the minimum quantum is one.
+			 */
+			XTRACE("quantum");
+			task->state = task_state_ready;
+			result = ISC_R_QUOTA;
+			break;
+		}
+	}
+
+done:
+	if (isc_refcount_decrement(&task->running) == 1 &&
+	    task->state == task_state_done)
+	{
+		finished = true;
+	}
+	UNLOCK(&task->lock);
+
+	if (finished) {
+		task_finished(task);
+	}
+
+	return (result);
+}
+
+isc_result_t
+isc_task_run(isc_task_t *task) {
+	return (task_run(task));
+}
+
+static void
+manager_free(isc_taskmgr_t *manager) {
+	isc_refcount_destroy(&manager->references);
+	isc_nm_detach(&manager->netmgr);
+
+	isc_mutex_destroy(&manager->lock);
+	manager->magic = 0;
+	isc_mem_putanddetach(&manager->mctx, manager, sizeof(*manager));
+}
+
+void
+isc_taskmgr_attach(isc_taskmgr_t *source, isc_taskmgr_t **targetp) {
+	REQUIRE(VALID_MANAGER(source));
+	REQUIRE(targetp != NULL && *targetp == NULL);
+
+	isc_refcount_increment(&source->references);
+
+	*targetp = source;
+}
+
+void
+isc_taskmgr_detach(isc_taskmgr_t **managerp) {
+	REQUIRE(managerp != NULL);
+	REQUIRE(VALID_MANAGER(*managerp));
+
+	isc_taskmgr_t *manager = *managerp;
+	*managerp = NULL;
+
+	if (isc_refcount_decrement(&manager->references) == 1) {
+		manager_free(manager);
+	}
+}
+
+isc_result_t
+isc__taskmgr_create(isc_mem_t *mctx, unsigned int default_quantum, isc_nm_t *nm,
+		    isc_taskmgr_t **managerp) {
+	isc_taskmgr_t *manager;
+
+	/*
+	 * Create a new task manager.
+	 */
+
+	REQUIRE(managerp != NULL && *managerp == NULL);
+	REQUIRE(nm != NULL);
+
+	manager = isc_mem_get(mctx, sizeof(*manager));
+	*manager = (isc_taskmgr_t){ .magic = TASK_MANAGER_MAGIC };
+
+	isc_mutex_init(&manager->lock);
+
+	if (default_quantum == 0) {
+		default_quantum = DEFAULT_DEFAULT_QUANTUM;
+	}
+	manager->default_quantum = default_quantum;
+
+	if (nm != NULL) {
+		isc_nm_attach(nm, &manager->netmgr);
+	}
+
+	INIT_LIST(manager->tasks);
+	atomic_init(&manager->mode, isc_taskmgrmode_normal);
+	atomic_init(&manager->exclusive_req, false);
+	atomic_init(&manager->tasks_count, 0);
+
+	isc_mem_attach(mctx, &manager->mctx);
+
+	isc_refcount_init(&manager->references, 1);
+
+	*managerp = manager;
+
+	return (ISC_R_SUCCESS);
+}
+
+void
+isc__taskmgr_shutdown(isc_taskmgr_t *manager) {
+	isc_task_t *task;
+
+	REQUIRE(VALID_MANAGER(manager));
+
+	XTHREADTRACE("isc_taskmgr_shutdown");
+	/*
+	 * Only one non-worker thread may ever call this routine.
+	 * If a worker thread wants to initiate shutdown of the
+	 * task manager, it should ask some non-worker thread to call
+	 * isc_taskmgr_destroy(), e.g. by signalling a condition variable
+	 * that the startup thread is sleeping on.
+	 */
+
+	/*
+	 * Unlike elsewhere, we're going to hold this lock a long time.
+	 * We need to do so, because otherwise the list of tasks could
+	 * change while we were traversing it.
+	 *
+	 * This is also the only function where we will hold both the
+	 * task manager lock and a task lock at the same time.
+	 */
+	LOCK(&manager->lock);
+	if (manager->excl != NULL) {
+		isc_task_detach((isc_task_t **)&manager->excl);
+	}
+
+	/*
+	 * Make sure we only get called once.
+	 */
+	INSIST(manager->exiting == false);
+	manager->exiting = true;
+
+	/*
+	 * Post shutdown event(s) to every task (if they haven't already been
+	 * posted).
+	 */
+	for (task = HEAD(manager->tasks); task != NULL; task = NEXT(task, link))
+	{
+		bool was_idle;
+
+		LOCK(&task->lock);
+		was_idle = task_shutdown(task);
+		UNLOCK(&task->lock);
+
+		if (was_idle) {
+			task_ready(task);
+		}
+	}
+
+	UNLOCK(&manager->lock);
+}
+
+void
+isc__taskmgr_destroy(isc_taskmgr_t **managerp) {
+	REQUIRE(managerp != NULL && VALID_MANAGER(*managerp));
+	XTHREADTRACE("isc_taskmgr_destroy");
+
+#ifdef ISC_TASK_TRACE
+	int counter = 0;
+	while (isc_refcount_current(&(*managerp)->references) > 1 &&
+	       counter++ < 1000)
+	{
+		usleep(10 * 1000);
+	}
+	INSIST(counter < 1000);
+#else
+	while (isc_refcount_current(&(*managerp)->references) > 1) {
+		usleep(10 * 1000);
+	}
+#endif
+
+	isc_taskmgr_detach(managerp);
+}
+
+void
+isc_taskmgr_setexcltask(isc_taskmgr_t *mgr, isc_task_t *task) {
+	REQUIRE(VALID_MANAGER(mgr));
+	REQUIRE(VALID_TASK(task));
+
+	LOCK(&task->lock);
+	REQUIRE(task->threadid == 0);
+	UNLOCK(&task->lock);
+
+	LOCK(&mgr->lock);
+	if (mgr->excl != NULL) {
+		isc_task_detach(&mgr->excl);
+	}
+	isc_task_attach(task, &mgr->excl);
+	UNLOCK(&mgr->lock);
+}
+
+isc_result_t
+isc_taskmgr_excltask(isc_taskmgr_t *mgr, isc_task_t **taskp) {
+	isc_result_t result;
+
+	REQUIRE(VALID_MANAGER(mgr));
+	REQUIRE(taskp != NULL && *taskp == NULL);
+
+	LOCK(&mgr->lock);
+	if (mgr->excl != NULL) {
+		isc_task_attach(mgr->excl, taskp);
+		result = ISC_R_SUCCESS;
+	} else if (mgr->exiting) {
+		result = ISC_R_SHUTTINGDOWN;
+	} else {
+		result = ISC_R_NOTFOUND;
+	}
+	UNLOCK(&mgr->lock);
+
+	return (result);
+}
+
+isc_result_t
+isc_task_beginexclusive(isc_task_t *task) {
+	isc_taskmgr_t *manager;
+
+	REQUIRE(VALID_TASK(task));
+
+	manager = task->manager;
+
+	REQUIRE(task->state == task_state_running);
+
+	LOCK(&manager->lock);
+	REQUIRE(task == manager->excl ||
+		(manager->exiting && manager->excl == NULL));
+	UNLOCK(&manager->lock);
+
+	if (!atomic_compare_exchange_strong(&manager->exclusive_req,
+					    &(bool){ false }, true))
+	{
+		return (ISC_R_LOCKBUSY);
+	}
+
+	if (isc_log_wouldlog(isc_lctx, ISC_LOG_DEBUG(1))) {
+		isc_log_write(isc_lctx, ISC_LOGCATEGORY_GENERAL,
+			      ISC_LOGMODULE_OTHER, ISC_LOG_DEBUG(1),
+			      "exclusive task mode: %s", "starting");
+	}
+
+	isc_nm_pause(manager->netmgr);
+
+	if (isc_log_wouldlog(isc_lctx, ISC_LOG_DEBUG(1))) {
+		isc_log_write(isc_lctx, ISC_LOGCATEGORY_GENERAL,
+			      ISC_LOGMODULE_OTHER, ISC_LOG_DEBUG(1),
+			      "exclusive task mode: %s", "started");
+	}
+
+	return (ISC_R_SUCCESS);
+}
+
+void
+isc_task_endexclusive(isc_task_t *task) {
+	isc_taskmgr_t *manager = NULL;
+
+	REQUIRE(VALID_TASK(task));
+	REQUIRE(task->state == task_state_running);
+
+	manager = task->manager;
+
+	if (isc_log_wouldlog(isc_lctx, ISC_LOG_DEBUG(1))) {
+		isc_log_write(isc_lctx, ISC_LOGCATEGORY_GENERAL,
+			      ISC_LOGMODULE_OTHER, ISC_LOG_DEBUG(1),
+			      "exclusive task mode: %s", "ending");
+	}
+
+	isc_nm_resume(manager->netmgr);
+
+	if (isc_log_wouldlog(isc_lctx, ISC_LOG_DEBUG(1))) {
+		isc_log_write(isc_lctx, ISC_LOGCATEGORY_GENERAL,
+			      ISC_LOGMODULE_OTHER, ISC_LOG_DEBUG(1),
+			      "exclusive task mode: %s", "ended");
+	}
+
+	atomic_compare_exchange_enforced(&manager->exclusive_req,
+					 &(bool){ true }, false);
+}
+
+void
+isc_taskmgr_setmode(isc_taskmgr_t *manager, isc_taskmgrmode_t mode) {
+	atomic_store(&manager->mode, mode);
+}
+
+isc_taskmgrmode_t
+isc_taskmgr_mode(isc_taskmgr_t *manager) {
+	return (atomic_load(&manager->mode));
+}
+
+void
+isc_task_setprivilege(isc_task_t *task, bool priv) {
+	REQUIRE(VALID_TASK(task));
+
+	atomic_store_release(&task->privileged, priv);
+}
+
+bool
+isc_task_getprivilege(isc_task_t *task) {
+	REQUIRE(VALID_TASK(task));
+
+	return (TASK_PRIVILEGED(task));
+}
+
+bool
+isc_task_privileged(isc_task_t *task) {
+	REQUIRE(VALID_TASK(task));
+
+	return (isc_taskmgr_mode(task->manager) && TASK_PRIVILEGED(task));
+}
+
+bool
+isc_task_exiting(isc_task_t *task) {
+	REQUIRE(VALID_TASK(task));
+
+	return (TASK_SHUTTINGDOWN(task));
+}
+
+#ifdef HAVE_LIBXML2
+#define TRY0(a)                     \
+	do {                        \
+		xmlrc = (a);        \
+		if (xmlrc < 0)      \
+			goto error; \
+	} while (0)
+int
+isc_taskmgr_renderxml(isc_taskmgr_t *mgr, void *writer0) {
+	isc_task_t *task = NULL;
+	int xmlrc;
+	xmlTextWriterPtr writer = (xmlTextWriterPtr)writer0;
+
+	LOCK(&mgr->lock);
+
+	/*
+	 * Write out the thread-model, and some details about each depending
+	 * on which type is enabled.
+	 */
+	TRY0(xmlTextWriterStartElement(writer, ISC_XMLCHAR "thread-model"));
+	TRY0(xmlTextWriterStartElement(writer, ISC_XMLCHAR "type"));
+	TRY0(xmlTextWriterWriteString(writer, ISC_XMLCHAR "threaded"));
+	TRY0(xmlTextWriterEndElement(writer)); /* type */
+
+	TRY0(xmlTextWriterStartElement(writer, ISC_XMLCHAR "default-quantum"));
+	TRY0(xmlTextWriterWriteFormatString(writer, "%d",
+					    mgr->default_quantum));
+	TRY0(xmlTextWriterEndElement(writer)); /* default-quantum */
+
+	TRY0(xmlTextWriterEndElement(writer)); /* thread-model */
+
+	TRY0(xmlTextWriterStartElement(writer, ISC_XMLCHAR "tasks"));
+	task = ISC_LIST_HEAD(mgr->tasks);
+	while (task != NULL) {
+		LOCK(&task->lock);
+		TRY0(xmlTextWriterStartElement(writer, ISC_XMLCHAR "task"));
+
+		if (task->name[0] != 0) {
+			TRY0(xmlTextWriterStartElement(writer,
+						       ISC_XMLCHAR "name"));
+			TRY0(xmlTextWriterWriteFormatString(writer, "%s",
+							    task->name));
+			TRY0(xmlTextWriterEndElement(writer)); /* name */
+		}
+
+		TRY0(xmlTextWriterStartElement(writer, ISC_XMLCHAR "reference"
+								   "s"));
+		TRY0(xmlTextWriterWriteFormatString(
+			writer, "%" PRIuFAST32,
+			isc_refcount_current(&task->references)));
+		TRY0(xmlTextWriterEndElement(writer)); /* references */
+
+		TRY0(xmlTextWriterStartElement(writer, ISC_XMLCHAR "id"));
+		TRY0(xmlTextWriterWriteFormatString(writer, "%p", task));
+		TRY0(xmlTextWriterEndElement(writer)); /* id */
+
+		TRY0(xmlTextWriterStartElement(writer, ISC_XMLCHAR "state"));
+		TRY0(xmlTextWriterWriteFormatString(writer, "%s",
+						    statenames[task->state]));
+		TRY0(xmlTextWriterEndElement(writer)); /* state */
+
+		TRY0(xmlTextWriterStartElement(writer, ISC_XMLCHAR "quantum"));
+		TRY0(xmlTextWriterWriteFormatString(writer, "%d",
+						    task->quantum));
+		TRY0(xmlTextWriterEndElement(writer)); /* quantum */
+
+		TRY0(xmlTextWriterStartElement(writer, ISC_XMLCHAR "events"));
+		TRY0(xmlTextWriterWriteFormatString(writer, "%d",
+						    task->nevents));
+		TRY0(xmlTextWriterEndElement(writer)); /* events */
+
+		TRY0(xmlTextWriterEndElement(writer));
+
+		UNLOCK(&task->lock);
+		task = ISC_LIST_NEXT(task, link);
+	}
+	TRY0(xmlTextWriterEndElement(writer)); /* tasks */
+
+error:
+	if (task != NULL) {
+		UNLOCK(&task->lock);
+	}
+	UNLOCK(&mgr->lock);
+
+	return (xmlrc);
+}
+#endif /* HAVE_LIBXML2 */
+
+#ifdef HAVE_JSON_C
+#define CHECKMEM(m)                              \
+	do {                                     \
+		if (m == NULL) {                 \
+			result = ISC_R_NOMEMORY; \
+			goto error;              \
+		}                                \
+	} while (0)
+
+isc_result_t
+isc_taskmgr_renderjson(isc_taskmgr_t *mgr, void *tasks0) {
+	isc_result_t result = ISC_R_SUCCESS;
+	isc_task_t *task = NULL;
+	json_object *obj = NULL, *array = NULL, *taskobj = NULL;
+	json_object *tasks = (json_object *)tasks0;
+
+	LOCK(&mgr->lock);
+
+	/*
+	 * Write out the thread-model, and some details about each depending
+	 * on which type is enabled.
+	 */
+	obj = json_object_new_string("threaded");
+	CHECKMEM(obj);
+	json_object_object_add(tasks, "thread-model", obj);
+
+	obj = json_object_new_int(mgr->default_quantum);
+	CHECKMEM(obj);
+	json_object_object_add(tasks, "default-quantum", obj);
+
+	array = json_object_new_array();
+	CHECKMEM(array);
+
+	for (task = ISC_LIST_HEAD(mgr->tasks); task != NULL;
+	     task = ISC_LIST_NEXT(task, link))
+	{
+		char buf[255];
+
+		LOCK(&task->lock);
+
+		taskobj = json_object_new_object();
+		CHECKMEM(taskobj);
+		json_object_array_add(array, taskobj);
+
+		snprintf(buf, sizeof(buf), "%p", task);
+		obj = json_object_new_string(buf);
+		CHECKMEM(obj);
+		json_object_object_add(taskobj, "id", obj);
+
+		if (task->name[0] != 0) {
+			obj = json_object_new_string(task->name);
+			CHECKMEM(obj);
+			json_object_object_add(taskobj, "name", obj);
+		}
+
+		obj = json_object_new_int(
+			isc_refcount_current(&task->references));
+		CHECKMEM(obj);
+		json_object_object_add(taskobj, "references", obj);
+
+		obj = json_object_new_string(statenames[task->state]);
+		CHECKMEM(obj);
+		json_object_object_add(taskobj, "state", obj);
+
+		obj = json_object_new_int(task->quantum);
+		CHECKMEM(obj);
+		json_object_object_add(taskobj, "quantum", obj);
+
+		obj = json_object_new_int(task->nevents);
+		CHECKMEM(obj);
+		json_object_object_add(taskobj, "events", obj);
+
+		UNLOCK(&task->lock);
+	}
+
+	json_object_object_add(tasks, "tasks", array);
+	array = NULL;
+	result = ISC_R_SUCCESS;
+
+error:
+	if (array != NULL) {
+		json_object_put(array);
+	}
+
+	if (task != NULL) {
+		UNLOCK(&task->lock);
+	}
+	UNLOCK(&mgr->lock);
+
+	return (result);
+}
+#endif /* ifdef HAVE_JSON_C */