task.c revision a790a11730ee7c8ea702194694da9edae39dfc13
/*
* Copyright (C) 1998, 1999 Internet Software Consortium.
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM DISCLAIMS
* ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE
* CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
* DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
* PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
* ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
* SOFTWARE.
*/
/*
* Principal Author: Bob Halley
*/
/*
* XXXRTH Need to document the states a task can be in, and the rules
* for changing states.
*/
#include <config.h>
#include <string.h>
#include <isc/assertions.h>
#include <isc/condition.h>
#define ISC_TASK_NAMES 1
#ifdef ISC_TASK_TRACE
task, isc_thread_self(), (m))
(t), isc_thread_self(), (m))
isc_thread_self(), (m))
#else
#define XTRACE(m)
#define XTTRACE(t, m)
#define XTHREADTRACE(m)
#endif
/***
*** Types.
***/
typedef enum {
} task_state_t;
#define VALID_TASK(t) ((t) != NULL && \
(t)->magic == TASK_MAGIC)
struct isc_task {
/* Not locked. */
unsigned int magic;
/* Locked by task lock. */
unsigned int references;
unsigned int quantum;
unsigned int flags;
#ifdef ISC_TASK_NAMES
char name[16];
void * tag;
#endif
/* Locked by task manager lock. */
};
#define TASK_F_SHUTTINGDOWN 0x01
!= 0)
#define VALID_MANAGER(m) ((m) != NULL && \
(m)->magic == TASK_MANAGER_MAGIC)
struct isc_taskmgr {
/* Not locked. */
unsigned int magic;
unsigned int workers;
/* Locked by task manager lock. */
unsigned int default_quantum;
};
#define DEFAULT_DEFAULT_QUANTUM 5
/***
*** Tasks.
***/
static void
XTRACE("task_finished");
/*
* All tasks have completed and the
* task manager is exiting. Wake up
* any idle worker threads so they
* can exit.
*/
}
}
isc_task_t **taskp)
{
return (ISC_R_NOMEMORY);
XTRACE("create");
"isc_mutex_init() failed");
return (ISC_R_UNEXPECTED);
}
#ifdef ISC_TASK_NAMES
#endif
} else
if (exiting) {
return (ISC_R_SHUTTINGDOWN);
}
return (ISC_R_SUCCESS);
}
void
/*
* Attach *targetp to source.
*/
source->references++;
}
static inline isc_boolean_t
/*
* Caller must be holding the task's lock.
*/
XTRACE("task_shutdown");
if (! TASK_SHUTTINGDOWN(task)) {
XTRACE("shutting down");
}
/*
* Note that we post shutdown events LIFO.
*/
}
}
return (was_idle);
}
static inline void
XTRACE("task_ready");
}
static inline isc_boolean_t
/*
* Caller must be holding the task lock.
*/
XTRACE("detach");
task->references--;
/*
* 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() to deal with
* shutting down and termination.
*/
return (ISC_TRUE);
}
return (ISC_FALSE);
}
void
/*
* Detach *taskp from its task.
*/
XTRACE("isc_task_detach");
if (was_idle)
}
/*
* Get the task's memory context.
*/
}
static inline isc_boolean_t
/*
* Caller must be holding the task lock.
*/
XTRACE("task_send");
}
return (was_idle);
}
void
/*
* Send '*event' to '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.
*/
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.
*/
}
}
void
/*
* Send '*event' to '*taskp' and then detach '*taskp' from its
* task.
*/
XTRACE("isc_task_sendanddetach");
/*
* 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.
*/
}
static unsigned int
{
unsigned int count = 0;
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".
*/
count++;
}
}
return (count);
}
unsigned int
{
unsigned int count;
/*
* Purge events from a task's event queue.
*/
XTRACE("isc_task_purgerange");
ISC_TRUE);
}
/*
* Note that purging never changes the state of the task.
*/
return (count);
}
unsigned int
void *tag)
{
/*
* Purge events from a task's event queue.
*/
XTRACE("isc_task_purge");
}
/*
* Purge 'event' from a task's event queue.
*
* XXXRTH: WARNING: This method may be removed before beta.
*/
/*
* 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.
*/
curr_event != NULL;
curr_event = next_event) {
break;
}
}
if (curr_event == NULL)
return (ISC_FALSE);
return (ISC_TRUE);
}
unsigned int
{
/*
* Remove events from a task's event queue.
*/
XTRACE("isc_task_unsendrange");
ISC_FALSE));
}
unsigned int
{
/*
* Remove events from a task's event queue.
*/
XTRACE("isc_task_unsend");
ISC_FALSE));
}
/*
* Send a shutdown event with action 'action' and argument 'arg' when
* 'task' is shutdown.
*/
NULL,
arg,
sizeof *event);
return (ISC_R_NOMEMORY);
if (TASK_SHUTTINGDOWN(task)) {
} else
if (disallowed)
return (result);
}
void
/*
* Shutdown 'task'.
*/
if (was_idle)
}
void
/*
* Destroy '*taskp'.
*/
}
void
/*
* Name 'task'.
*/
#ifdef ISC_TASK_NAMES
#else
(void)name;
(void)tag;
#endif
}
/***
*** Task Manager.
***/
static isc_threadresult_t
#ifdef _WIN32
#endif
XTHREADTRACE("start");
/*
* Again we're trying to hold the lock for as short a time as possible
* and to do as little locking and unlocking as possible.
*
* In both while loops, the appropriate lock must be held before the
* while body starts. Code which acquired the lock at the top of
* the loop would be more readable, but would result in a lot of
* extra locking. Compare:
*
* Straightforward:
*
* LOCK();
* ...
* UNLOCK();
* while (expression) {
* LOCK();
* ...
* UNLOCK();
*
* Unlocked part here...
*
* LOCK();
* ...
* UNLOCK();
* }
*
* Note how if the loop continues we unlock and then immediately lock.
* For N iterations of the loop, this code does 2N+1 locks and 2N+1
* unlocks. Also note that the lock is not held when the while
* condition is tested, which may or may not be important, depending
* on the expression.
*
* As written:
*
* LOCK();
* while (expression) {
* ...
* UNLOCK();
*
* Unlocked part here...
*
* LOCK();
* ...
* }
* UNLOCK();
*
* For N iterations of the loop, this code does N+1 locks and N+1
* unlocks. The while expression is always protected by the lock.
*/
/*
* For reasons similar to those given in the comment in
* isc_task_send() above, it is safe for us to dequeue
* the task while only holding the manager lock, and then
* change the task to running state while only holding the
* task lock.
*/
XTHREADTRACE("wait");
XTHREADTRACE("awake");
}
XTHREADTRACE("working");
unsigned int dispatch_count = 0;
/*
* Note we only unlock the manager lock if we actually
* have a task to do. We must reacquire the manager
* lock before exiting the 'if (task != NULL)' block.
*/
XTRACE("running");
do {
/*
* Execute the event action.
*/
XTRACE("execute action");
}
}
if (task->references == 0 &&
!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.
*/
}
/*
* Nothing else to do for this task
* right now.
*/
XTRACE("empty");
if (task->references == 0 &&
/*
* The task is done.
*/
XTRACE("done");
} else
/*
* 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");
}
} while (!done);
if (finished)
if (requeue) {
/*
* We know we're awake, so we don't have
* to wakeup any sleeping threads if the
* ready queue is empty before we requeue.
*
* A possible optimization if the queue is
* empty is to 'goto' the 'if (task != NULL)'
* block, avoiding the ENQUEUE of the task
* and the subsequent immediate DEQUEUE
* (since it is the only executable task).
* We don't do this because then we'd be
* skipping the exit_requested check. The
* cost of ENQUEUE is low anyway, especially
* when you consider that we'd have to do
* an extra EMPTY check to see if we could
* do the optimization. If the ready queue
* were usually nonempty, the 'optimization'
* might even hurt rather than help.
*/
}
}
}
XTHREADTRACE("exit");
return ((isc_threadresult_t)0);
}
static void
}
{
unsigned int i, started = 0;
/*
* Create a new task manager.
*/
return (ISC_R_NOMEMORY);
return (ISC_R_NOMEMORY);
}
"isc_mutex_init() failed");
return (ISC_R_UNEXPECTED);
}
if (default_quantum == 0)
"isc_condition_init() failed");
return (ISC_R_UNEXPECTED);
}
/*
* Start workers.
*/
for (i = 0; i < workers; i++) {
started++;
}
}
if (started == 0) {
return (ISC_R_NOTHREADS);
}
return (ISC_R_SUCCESS);
}
void
unsigned int i;
/*
* Destroy '*managerp'.
*/
XTHREADTRACE("isc_taskmgr_destroy");
/*
* 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.
*/
/*
* Make sure we only get called once.
*/
/*
* Post shutdown event(s) to every task (if they haven't already been
* posted).
*/
if (task_shutdown(task))
}
/*
* Wake up any sleeping workers. This ensures we get work done if
* there's work left to do, and if there are already no tasks left
* it will cause the workers to see manager->exiting.
*/
/*
* Wait for all the worker threads to exit.
*/
}