thread_sync.c

root/thread_sync.c

/* */
DEFINITIONS

This source file includes following definitions.
mutex_free
mutex_memsize
rb_obj_is_mutex
mutex_alloc
mutex_initialize
rb_mutex_new
rb_mutex_locked_p
mutex_locked
rb_mutex_trylock
lock_func
lock_interrupt
rb_mutex_lock
rb_mutex_owned_p
rb_mutex_unlock_th
rb_mutex_unlock
rb_mutex_abandon_keeping_mutexes
rb_mutex_abandon_locking_mutex
rb_mutex_abandon_all
rb_mutex_sleep_forever
rb_mutex_wait_for
rb_mutex_sleep
mutex_sleep
rb_mutex_synchronize
rb_mutex_synchronize_m
rb_mutex_allow_trap
ary_buf_new
get_array
wakeup_first_thread
wakeup_all_threads
queue_length
queue_num_waiting
szqueue_num_waiting_producer
queue_closed_p
raise_closed_queue_error
queue_closed_result
queue_do_close
rb_queue_initialize
queue_do_push
rb_queue_close
rb_queue_closed_p
rb_queue_push
queue_delete_from_waiting
queue_sleep
queue_do_pop
queue_pop_should_block
rb_queue_pop
rb_queue_empty_p
rb_queue_clear
rb_queue_length
rb_queue_num_waiting
rb_szqueue_initialize
rb_szqueue_close
rb_szqueue_max_get
rb_szqueue_max_set
szqueue_push_should_block
rb_szqueue_push
szqueue_do_pop
rb_szqueue_pop
rb_szqueue_clear
rb_szqueue_num_waiting
rb_condvar_initialize
do_sleep
delete_current_thread
rb_condvar_wait
rb_condvar_signal
rb_condvar_broadcast
undumpable
Init_thread_sync
/* included by thread.c */

static VALUE rb_cMutex, rb_cQueue, rb_cSizedQueue, rb_cConditionVariable;
static VALUE rb_eClosedQueueError;

/* Mutex */

typedef struct rb_mutex_struct {
    rb_nativethread_lock_t lock;
    rb_nativethread_cond_t cond;
    struct rb_thread_struct volatile *th;
    struct rb_mutex_struct *next_mutex;
    int cond_waiting;
    int allow_trap;
} rb_mutex_t;

#if defined(HAVE_WORKING_FORK)
static void rb_mutex_abandon_all(rb_mutex_t *mutexes);
static void rb_mutex_abandon_keeping_mutexes(rb_thread_t *th);
static void rb_mutex_abandon_locking_mutex(rb_thread_t *th);
#endif
static const char* rb_mutex_unlock_th(rb_mutex_t *mutex, rb_thread_t volatile *th);

/*
 *  Document-class: Mutex
 *
 *  Mutex implements a simple semaphore that can be used to coordinate access to
 *  shared data from multiple concurrent threads.
 *
 *  Example:
 *
 *    require 'thread'
 *    semaphore = Mutex.new
 *
 *    a = Thread.new {
 *      semaphore.synchronize {
 *        # access shared resource
 *      }
 *    }
 *
 *    b = Thread.new {
 *      semaphore.synchronize {
 *        # access shared resource
 *      }
 *    }
 *
 */

#define GetMutexPtr(obj, tobj) \
    TypedData_Get_Struct((obj), rb_mutex_t, &mutex_data_type, (tobj))

#define mutex_mark NULL

static void
mutex_free(void *ptr)
{
    if (ptr) {
        rb_mutex_t *mutex = ptr;
        if (mutex->th) {
            /* rb_warn("free locked mutex"); */
            const char *err = rb_mutex_unlock_th(mutex, mutex->th);
            if (err) rb_bug("%s", err);
        }
        native_mutex_destroy(&mutex->lock);
        native_cond_destroy(&mutex->cond);
    }
    ruby_xfree(ptr);
}

static size_t
mutex_memsize(const void *ptr)
{
    return sizeof(rb_mutex_t);
}

static const rb_data_type_t mutex_data_type = {
    "mutex",
    {mutex_mark, mutex_free, mutex_memsize,},
    0, 0, RUBY_TYPED_FREE_IMMEDIATELY
};

VALUE
rb_obj_is_mutex(VALUE obj)
{
    if (rb_typeddata_is_kind_of(obj, &mutex_data_type)) {
        return Qtrue;
    }
    else {
        return Qfalse;
    }
}

static VALUE
mutex_alloc(VALUE klass)
{
    VALUE obj;
    rb_mutex_t *mutex;

    obj = TypedData_Make_Struct(klass, rb_mutex_t, &mutex_data_type, mutex);
    native_mutex_initialize(&mutex->lock);
    native_cond_initialize(&mutex->cond, RB_CONDATTR_CLOCK_MONOTONIC);
    return obj;
}

/*
 *  call-seq:
 *     Mutex.new   -> mutex
 *
 *  Creates a new Mutex
 */
static VALUE
mutex_initialize(VALUE self)
{
    return self;
}

VALUE
rb_mutex_new(void)
{
    return mutex_alloc(rb_cMutex);
}

/*
 * call-seq:
 *    mutex.locked?  -> true or false
 *
 * Returns +true+ if this lock is currently held by some thread.
 */
VALUE
rb_mutex_locked_p(VALUE self)
{
    rb_mutex_t *mutex;
    GetMutexPtr(self, mutex);
    return mutex->th ? Qtrue : Qfalse;
}

static void
mutex_locked(rb_thread_t *th, VALUE self)
{
    rb_mutex_t *mutex;
    GetMutexPtr(self, mutex);

    if (th->keeping_mutexes) {
        mutex->next_mutex = th->keeping_mutexes;
    }
    th->keeping_mutexes = mutex;
}

/*
 * call-seq:
 *    mutex.try_lock  -> true or false
 *
 * Attempts to obtain the lock and returns immediately. Returns +true+ if the
 * lock was granted.
 */
VALUE
rb_mutex_trylock(VALUE self)
{
    rb_mutex_t *mutex;
    VALUE locked = Qfalse;
    GetMutexPtr(self, mutex);

    native_mutex_lock(&mutex->lock);
    if (mutex->th == 0) {
        rb_thread_t *th = GET_THREAD();
        mutex->th = th;
        locked = Qtrue;

        mutex_locked(th, self);
    }
    native_mutex_unlock(&mutex->lock);

    return locked;
}

static int
lock_func(rb_thread_t *th, rb_mutex_t *mutex, int timeout_ms)
{
    int interrupted = 0;
    int err = 0;

    mutex->cond_waiting++;
    for (;;) {
        if (!mutex->th) {
            mutex->th = th;
            break;
        }
        if (RUBY_VM_INTERRUPTED(th)) {
            interrupted = 1;
            break;
        }
        if (err == ETIMEDOUT) {
            interrupted = 2;
            break;
        }

        if (timeout_ms) {
            struct timespec timeout_rel;
            struct timespec timeout;

            timeout_rel.tv_sec = 0;
            timeout_rel.tv_nsec = timeout_ms * 1000 * 1000;
            timeout = native_cond_timeout(&mutex->cond, timeout_rel);
            err = native_cond_timedwait(&mutex->cond, &mutex->lock, &timeout);
        }
        else {
            native_cond_wait(&mutex->cond, &mutex->lock);
            err = 0;
        }
    }
    mutex->cond_waiting--;

    return interrupted;
}

static void
lock_interrupt(void *ptr)
{
    rb_mutex_t *mutex = (rb_mutex_t *)ptr;
    native_mutex_lock(&mutex->lock);
    if (mutex->cond_waiting > 0)
        native_cond_broadcast(&mutex->cond);
    native_mutex_unlock(&mutex->lock);
}

/*
 * At maximum, only one thread can use cond_timedwait and watch deadlock
 * periodically. Multiple polling thread (i.e. concurrent deadlock check)
 * introduces new race conditions. [Bug #6278] [ruby-core:44275]
 */
static const rb_thread_t *patrol_thread = NULL;

/*
 * call-seq:
 *    mutex.lock  -> self
 *
 * Attempts to grab the lock and waits if it isn't available.
 * Raises +ThreadError+ if +mutex+ was locked by the current thread.
 */
VALUE
rb_mutex_lock(VALUE self)
{
    rb_thread_t *th = GET_THREAD();
    rb_mutex_t *mutex;
    GetMutexPtr(self, mutex);

    /* When running trap handler */
    if (!mutex->allow_trap && th->interrupt_mask & TRAP_INTERRUPT_MASK) {
        rb_raise(rb_eThreadError, "can't be called from trap context");
    }

    if (rb_mutex_trylock(self) == Qfalse) {
        if (mutex->th == th) {
            rb_raise(rb_eThreadError, "deadlock; recursive locking");
        }

        while (mutex->th != th) {
            int interrupted;
            enum rb_thread_status prev_status = th->status;
            volatile int timeout_ms = 0;
            struct rb_unblock_callback oldubf;

            set_unblock_function(th, lock_interrupt, mutex, &oldubf, FALSE);
            th->status = THREAD_STOPPED_FOREVER;
            th->locking_mutex = self;

            native_mutex_lock(&mutex->lock);
            th->vm->sleeper++;
            /*
             * Carefully! while some contended threads are in lock_func(),
             * vm->sleepr is unstable value. we have to avoid both deadlock
             * and busy loop.
             */
            if ((vm_living_thread_num(th->vm) == th->vm->sleeper) &&
                !patrol_thread) {
                timeout_ms = 100;
                patrol_thread = th;
            }

            GVL_UNLOCK_BEGIN();
            interrupted = lock_func(th, mutex, (int)timeout_ms);
            native_mutex_unlock(&mutex->lock);
            GVL_UNLOCK_END();

            if (patrol_thread == th)
                patrol_thread = NULL;

            reset_unblock_function(th, &oldubf);

            th->locking_mutex = Qfalse;
            if (mutex->th && interrupted == 2) {
                rb_check_deadlock(th->vm);
            }
            if (th->status == THREAD_STOPPED_FOREVER) {
                th->status = prev_status;
            }
            th->vm->sleeper--;

            if (mutex->th == th) mutex_locked(th, self);

            if (interrupted) {
                RUBY_VM_CHECK_INTS_BLOCKING(th);
            }
        }
    }
    return self;
}

/*
 * call-seq:
 *    mutex.owned?  -> true or false
 *
 * Returns +true+ if this lock is currently held by current thread.
 */
VALUE
rb_mutex_owned_p(VALUE self)
{
    VALUE owned = Qfalse;
    rb_thread_t *th = GET_THREAD();
    rb_mutex_t *mutex;

    GetMutexPtr(self, mutex);

    if (mutex->th == th)
        owned = Qtrue;

    return owned;
}

static const char *
rb_mutex_unlock_th(rb_mutex_t *mutex, rb_thread_t volatile *th)
{
    const char *err = NULL;

    native_mutex_lock(&mutex->lock);

    if (mutex->th == 0) {
        err = "Attempt to unlock a mutex which is not locked";
    }
    else if (mutex->th != th) {
        err = "Attempt to unlock a mutex which is locked by another thread";
    }
    else {
        mutex->th = 0;
        if (mutex->cond_waiting > 0)
            native_cond_signal(&mutex->cond);
    }

    native_mutex_unlock(&mutex->lock);

    if (!err) {
        rb_mutex_t *volatile *th_mutex = &th->keeping_mutexes;
        while (*th_mutex != mutex) {
            th_mutex = &(*th_mutex)->next_mutex;
        }
        *th_mutex = mutex->next_mutex;
        mutex->next_mutex = NULL;
    }

    return err;
}

/*
 * call-seq:
 *    mutex.unlock    -> self
 *
 * Releases the lock.
 * Raises +ThreadError+ if +mutex+ wasn't locked by the current thread.
 */
VALUE
rb_mutex_unlock(VALUE self)
{
    const char *err;
    rb_mutex_t *mutex;
    GetMutexPtr(self, mutex);

    err = rb_mutex_unlock_th(mutex, GET_THREAD());
    if (err) rb_raise(rb_eThreadError, "%s", err);

    return self;
}

#if defined(HAVE_WORKING_FORK)
static void
rb_mutex_abandon_keeping_mutexes(rb_thread_t *th)
{
    if (th->keeping_mutexes) {
        rb_mutex_abandon_all(th->keeping_mutexes);
    }
    th->keeping_mutexes = NULL;
}

static void
rb_mutex_abandon_locking_mutex(rb_thread_t *th)
{
    rb_mutex_t *mutex;

    if (!th->locking_mutex) return;

    GetMutexPtr(th->locking_mutex, mutex);
    if (mutex->th == th)
        rb_mutex_abandon_all(mutex);
    th->locking_mutex = Qfalse;
}

static void
rb_mutex_abandon_all(rb_mutex_t *mutexes)
{
    rb_mutex_t *mutex;

    while (mutexes) {
        mutex = mutexes;
        mutexes = mutex->next_mutex;
        mutex->th = 0;
        mutex->next_mutex = 0;
    }
}
#endif

static VALUE
rb_mutex_sleep_forever(VALUE time)
{
    sleep_forever(GET_THREAD(), 1, 0); /* permit spurious check */
    return Qnil;
}

static VALUE
rb_mutex_wait_for(VALUE time)
{
    struct timeval *t = (struct timeval *)time;
    sleep_timeval(GET_THREAD(), *t, 0); /* permit spurious check */
    return Qnil;
}

VALUE
rb_mutex_sleep(VALUE self, VALUE timeout)
{
    time_t beg, end;
    struct timeval t;

    if (!NIL_P(timeout)) {
        t = rb_time_interval(timeout);
    }
    rb_mutex_unlock(self);
    beg = time(0);
    if (NIL_P(timeout)) {
        rb_ensure(rb_mutex_sleep_forever, Qnil, rb_mutex_lock, self);
    }
    else {
        rb_ensure(rb_mutex_wait_for, (VALUE)&t, rb_mutex_lock, self);
    }
    end = time(0) - beg;
    return INT2FIX(end);
}

/*
 * call-seq:
 *    mutex.sleep(timeout = nil)    -> number
 *
 * Releases the lock and sleeps +timeout+ seconds if it is given and
 * non-nil or forever.  Raises +ThreadError+ if +mutex+ wasn't locked by
 * the current thread.
 *
 * When the thread is next woken up, it will attempt to reacquire
 * the lock.
 *
 * Note that this method can wakeup without explicit Thread#wakeup call.
 * For example, receiving signal and so on.
 */
static VALUE
mutex_sleep(int argc, VALUE *argv, VALUE self)
{
    VALUE timeout;

    rb_scan_args(argc, argv, "01", &timeout);
    return rb_mutex_sleep(self, timeout);
}

/*
 * call-seq:
 *    mutex.synchronize { ... }    -> result of the block
 *
 * Obtains a lock, runs the block, and releases the lock when the block
 * completes.  See the example under +Mutex+.
 */

VALUE
rb_mutex_synchronize(VALUE mutex, VALUE (*func)(VALUE arg), VALUE arg)
{
    rb_mutex_lock(mutex);
    return rb_ensure(func, arg, rb_mutex_unlock, mutex);
}

/*
 * call-seq:
 *    mutex.synchronize { ... }    -> result of the block
 *
 * Obtains a lock, runs the block, and releases the lock when the block
 * completes.  See the example under +Mutex+.
 */
static VALUE
rb_mutex_synchronize_m(VALUE self, VALUE args)
{
    if (!rb_block_given_p()) {
        rb_raise(rb_eThreadError, "must be called with a block");
    }

    return rb_mutex_synchronize(self, rb_yield, Qundef);
}

void rb_mutex_allow_trap(VALUE self, int val)
{
    rb_mutex_t *m;
    GetMutexPtr(self, m);

    m->allow_trap = val;
}

/* Queue */

enum {
    QUEUE_QUE,
    QUEUE_WAITERS,
    SZQUEUE_WAITERS,
    SZQUEUE_MAX,
    END_QUEUE
};

#define QUEUE_CLOSED          FL_USER5

#define GET_QUEUE_QUE(q)        get_array((q), QUEUE_QUE)
#define GET_QUEUE_WAITERS(q)    get_array((q), QUEUE_WAITERS)
#define GET_SZQUEUE_WAITERS(q)  get_array((q), SZQUEUE_WAITERS)
#define GET_SZQUEUE_MAX(q)      RSTRUCT_GET((q), SZQUEUE_MAX)
#define GET_SZQUEUE_ULONGMAX(q) NUM2ULONG(GET_SZQUEUE_MAX(q))

static VALUE
ary_buf_new(void)
{
    return rb_ary_tmp_new(1);
}

static VALUE
get_array(VALUE obj, int idx)
{
    VALUE ary = RSTRUCT_GET(obj, idx);
    if (!RB_TYPE_P(ary, T_ARRAY)) {
        rb_raise(rb_eTypeError, "%+"PRIsVALUE" not initialized", obj);
    }
    return ary;
}

static void
wakeup_first_thread(VALUE list)
{
    VALUE thread;

    while (!NIL_P(thread = rb_ary_shift(list))) {
        if (RTEST(rb_thread_wakeup_alive(thread))) break;
    }
}

static void
wakeup_all_threads(VALUE list)
{
    VALUE thread;
    long i;

    for (i=0; i<RARRAY_LEN(list); i++) {
        thread = RARRAY_AREF(list, i);
        rb_thread_wakeup_alive(thread);
    }
    rb_ary_clear(list);
}

static unsigned long
queue_length(VALUE self)
{
    VALUE que = GET_QUEUE_QUE(self);
    return RARRAY_LEN(que);
}

static unsigned long
queue_num_waiting(VALUE self)
{
    VALUE waiters = GET_QUEUE_WAITERS(self);
    return RARRAY_LEN(waiters);
}

static unsigned long
szqueue_num_waiting_producer(VALUE self)
{
    VALUE waiters = GET_SZQUEUE_WAITERS(self);
    return RARRAY_LEN(waiters);
}

static int
queue_closed_p(VALUE self)
{
    return FL_TEST_RAW(self, QUEUE_CLOSED) != 0;
}

static void
raise_closed_queue_error(VALUE self)
{
    rb_raise(rb_eClosedQueueError, "queue closed");
}

static VALUE
queue_closed_result(VALUE self)
{
    assert(queue_length(self) == 0);
    return Qnil;
}

static VALUE
queue_do_close(VALUE self, int is_szq)
{
    if (!queue_closed_p(self)) {
        FL_SET(self, QUEUE_CLOSED);

        if (queue_num_waiting(self) > 0) {
            VALUE waiters = GET_QUEUE_WAITERS(self);
            wakeup_all_threads(waiters);
        }

        if (is_szq && szqueue_num_waiting_producer(self) > 0) {
            VALUE waiters = GET_SZQUEUE_WAITERS(self);
            wakeup_all_threads(waiters);
        }
    }

    return self;
}

/*
 *  Document-class: Queue
 *
 *  The Queue class implements multi-producer, multi-consumer queues.
 *  It is especially useful in threaded programming when information
 *  must be exchanged safely between multiple threads. The Queue class
 *  implements all the required locking semantics.
 *
 *  The class implements FIFO type of queue. In a FIFO queue, the first
 *  tasks added are the first retrieved.
 *
 *  Example:
 *
 *      require 'thread'
 *      queue = Queue.new
 *
 *      producer = Thread.new do
 *        5.times do |i|
 *           sleep rand(i) # simulate expense
 *           queue << i
 *           puts "#{i} produced"
 *        end
 *      end
 *
 *      consumer = Thread.new do
 *        5.times do |i|
 *           value = queue.pop
 *           sleep rand(i/2) # simulate expense
 *           puts "consumed #{value}"
 *        end
 *      end
 *
 */

/*
 * Document-method: Queue::new
 *
 * Creates a new queue instance.
 */

static VALUE
rb_queue_initialize(VALUE self)
{
    RSTRUCT_SET(self, QUEUE_QUE, ary_buf_new());
    RSTRUCT_SET(self, QUEUE_WAITERS, ary_buf_new());
    return self;
}

static VALUE
queue_do_push(VALUE self, VALUE obj)
{
    if (queue_closed_p(self)) {
        raise_closed_queue_error(self);
    }
    rb_ary_push(GET_QUEUE_QUE(self), obj);
    wakeup_first_thread(GET_QUEUE_WAITERS(self));
    return self;
}

/*
 * Document-method: Queue#close
 * call-seq:
 *   close
 *
 * Closes the queue. A closed queue cannot be re-opened.
 *
 * After the call to close completes, the following are true:
 *
 * - +closed?+ will return true
 *
 * - +close+ will be ignored.
 *
 * - calling enq/push/<< will return nil.
 *
 * - when +empty?+ is false, calling deq/pop/shift will return an object
 *   from the queue as usual.
 *
 * ClosedQueueError is inherited from StopIteration, so that you can break loop block.
 *
 *  Example:
 *
 *      q = Queue.new
 *      Thread.new{
 *        while e = q.deq # wait for nil to break loop
 *          # ...
 *        end
 *      }
 *      q.close
 */

static VALUE
rb_queue_close(VALUE self)
{
    return queue_do_close(self, FALSE);
}

/*
 * Document-method: Queue#closed?
 * call-seq: closed?
 *
 * Returns +true+ if the queue is closed.
 */

static VALUE
rb_queue_closed_p(VALUE self)
{
    return queue_closed_p(self) ? Qtrue : Qfalse;
}

/*
 * Document-method: Queue#push
 * call-seq:
 *   push(object)
 *   enq(object)
 *   <<(object)
 *
 * Pushes the given +object+ to the queue.
 */

static VALUE
rb_queue_push(VALUE self, VALUE obj)
{
    return queue_do_push(self, obj);
}

struct waiting_delete {
    VALUE waiting;
    VALUE th;
};

static VALUE
queue_delete_from_waiting(struct waiting_delete *p)
{
    rb_ary_delete(p->waiting, p->th);
    return Qnil;
}

static VALUE
queue_sleep(VALUE arg)
{
    rb_thread_sleep_deadly();
    return Qnil;
}

static VALUE
queue_do_pop(VALUE self, int should_block)
{
    struct waiting_delete args;
    args.waiting = GET_QUEUE_WAITERS(self);
    args.th      = rb_thread_current();

    while (queue_length(self) == 0) {
        if (!should_block) {
            rb_raise(rb_eThreadError, "queue empty");
        }
        else if (queue_closed_p(self)) {
            return queue_closed_result(self);
        }
        else {
            assert(queue_length(self) == 0);
            assert(queue_closed_p(self) == 0);

            rb_ary_push(args.waiting, args.th);
            rb_ensure(queue_sleep, Qfalse, queue_delete_from_waiting, (VALUE)&args);
        }
    }

    return rb_ary_shift(GET_QUEUE_QUE(self));
}

static int
queue_pop_should_block(int argc, const VALUE *argv)
{
    int should_block = 1;
    rb_check_arity(argc, 0, 1);
    if (argc > 0) {
        should_block = !RTEST(argv[0]);
    }
    return should_block;
}

/*
 * Document-method: Queue#pop
 * call-seq:
 *   pop(non_block=false)
 *   deq(non_block=false)
 *   shift(non_block=false)
 *
 * Retrieves data from the queue.
 *
 * If the queue is empty, the calling thread is suspended until data is pushed
 * onto the queue. If +non_block+ is true, the thread isn't suspended, and an
 * exception is raised.
 */

static VALUE
rb_queue_pop(int argc, VALUE *argv, VALUE self)
{
    int should_block = queue_pop_should_block(argc, argv);
    return queue_do_pop(self, should_block);
}

/*
 * Document-method: Queue#empty?
 * call-seq: empty?
 *
 * Returns +true+ if the queue is empty.
 */

static VALUE
rb_queue_empty_p(VALUE self)
{
    return queue_length(self) == 0 ? Qtrue : Qfalse;
}

/*
 * Document-method: Queue#clear
 *
 * Removes all objects from the queue.
 */

static VALUE
rb_queue_clear(VALUE self)
{
    rb_ary_clear(GET_QUEUE_QUE(self));
    return self;
}

/*
 * Document-method: Queue#length
 * call-seq:
 *   length
 *   size
 *
 * Returns the length of the queue.
 */

static VALUE
rb_queue_length(VALUE self)
{
    unsigned long len = queue_length(self);
    return ULONG2NUM(len);
}

/*
 * Document-method: Queue#num_waiting
 *
 * Returns the number of threads waiting on the queue.
 */

static VALUE
rb_queue_num_waiting(VALUE self)
{
    unsigned long len = queue_num_waiting(self);
    return ULONG2NUM(len);
}

/*
 *  Document-class: SizedQueue
 *
 * This class represents queues of specified size capacity.  The push operation
 * may be blocked if the capacity is full.
 *
 * See Queue for an example of how a SizedQueue works.
 */

/*
 * Document-method: SizedQueue::new
 * call-seq: new(max)
 *
 * Creates a fixed-length queue with a maximum size of +max+.
 */

static VALUE
rb_szqueue_initialize(VALUE self, VALUE vmax)
{
    long max;

    max = NUM2LONG(vmax);
    if (max <= 0) {
        rb_raise(rb_eArgError, "queue size must be positive");
    }

    RSTRUCT_SET(self, QUEUE_QUE, ary_buf_new());
    RSTRUCT_SET(self, QUEUE_WAITERS, ary_buf_new());
    RSTRUCT_SET(self, SZQUEUE_WAITERS, ary_buf_new());
    RSTRUCT_SET(self, SZQUEUE_MAX, vmax);

    return self;
}

/*
 * Document-method: SizedQueue#close
 * call-seq:
 *   close
 *
 * Similar to Queue#close.
 *
 * The difference is behavior with waiting enqueuing threads.
 *
 * If there are waiting enqueuing threads, they are interrupted by
 * raising ClosedQueueError('queue closed').
 */
static VALUE
rb_szqueue_close(VALUE self)
{
    return queue_do_close(self, TRUE);
}

/*
 * Document-method: SizedQueue#max
 *
 * Returns the maximum size of the queue.
 */

static VALUE
rb_szqueue_max_get(VALUE self)
{
    return GET_SZQUEUE_MAX(self);
}

/*
 * Document-method: SizedQueue#max=
 * call-seq: max=(number)
 *
 * Sets the maximum size of the queue to the given +number+.
 */

static VALUE
rb_szqueue_max_set(VALUE self, VALUE vmax)
{
    long max = NUM2LONG(vmax), diff = 0;
    VALUE t;

    if (max <= 0) {
        rb_raise(rb_eArgError, "queue size must be positive");
    }
    if ((unsigned long)max > GET_SZQUEUE_ULONGMAX(self)) {
        diff = max - GET_SZQUEUE_ULONGMAX(self);
    }
    RSTRUCT_SET(self, SZQUEUE_MAX, vmax);
    while (diff-- > 0 && !NIL_P(t = rb_ary_shift(GET_SZQUEUE_WAITERS(self)))) {
        rb_thread_wakeup_alive(t);
    }
    return vmax;
}

static int
szqueue_push_should_block(int argc, const VALUE *argv)
{
    int should_block = 1;
    rb_check_arity(argc, 1, 2);
    if (argc > 1) {
        should_block = !RTEST(argv[1]);
    }
    return should_block;
}

/*
 * Document-method: SizedQueue#push
 * call-seq:
 *   push(object, non_block=false)
 *   enq(object, non_block=false)
 *   <<(object)
 *
 * Pushes +object+ to the queue.
 *
 * If there is no space left in the queue, waits until space becomes
 * available, unless +non_block+ is true.  If +non_block+ is true, the
 * thread isn't suspended, and an exception is raised.
 */

static VALUE
rb_szqueue_push(int argc, VALUE *argv, VALUE self)
{
    struct waiting_delete args;
    int should_block = szqueue_push_should_block(argc, argv);
    args.waiting = GET_SZQUEUE_WAITERS(self);
    args.th      = rb_thread_current();

    while (queue_length(self) >= GET_SZQUEUE_ULONGMAX(self)) {
        if (!should_block) {
            rb_raise(rb_eThreadError, "queue full");
        }
        else if (queue_closed_p(self)) {
            goto closed;
        }
        else {
            rb_ary_push(args.waiting, args.th);
            rb_ensure(queue_sleep, Qfalse, queue_delete_from_waiting, (VALUE)&args);
        }
    }

    if (queue_closed_p(self)) {
      closed:
        raise_closed_queue_error(self);
    }

    return queue_do_push(self, argv[0]);
}

static VALUE
szqueue_do_pop(VALUE self, int should_block)
{
    VALUE retval = queue_do_pop(self, should_block);

    if (queue_length(self) < GET_SZQUEUE_ULONGMAX(self)) {
        wakeup_first_thread(GET_SZQUEUE_WAITERS(self));
    }

    return retval;
}

/*
 * Document-method: SizedQueue#pop
 * call-seq:
 *   pop(non_block=false)
 *   deq(non_block=false)
 *   shift(non_block=false)
 *
 * Retrieves data from the queue.
 *
 * If the queue is empty, the calling thread is suspended until data is pushed
 * onto the queue. If +non_block+ is true, the thread isn't suspended, and an
 * exception is raised.
 */

static VALUE
rb_szqueue_pop(int argc, VALUE *argv, VALUE self)
{
    int should_block = queue_pop_should_block(argc, argv);
    return szqueue_do_pop(self, should_block);
}

/*
 * Document-method: Queue#clear
 *
 * Removes all objects from the queue.
 */

static VALUE
rb_szqueue_clear(VALUE self)
{
    rb_ary_clear(GET_QUEUE_QUE(self));
    wakeup_all_threads(GET_SZQUEUE_WAITERS(self));
    return self;
}

/*
 * Document-method: SizedQueue#num_waiting
 *
 * Returns the number of threads waiting on the queue.
 */

static VALUE
rb_szqueue_num_waiting(VALUE self)
{
    long len = queue_num_waiting(self) + szqueue_num_waiting_producer(self);
    return ULONG2NUM(len);
}

/* ConditionalVariable */

enum {
    CONDVAR_WAITERS,
    END_CONDVAR
};

#define GET_CONDVAR_WAITERS(cv) get_array((cv), CONDVAR_WAITERS)

/*
 *  Document-class: ConditionVariable
 *
 *  ConditionVariable objects augment class Mutex. Using condition variables,
 *  it is possible to suspend while in the middle of a critical section until a
 *  resource becomes available.
 *
 *  Example:
 *
 *    require 'thread'
 *
 *    mutex = Mutex.new
 *    resource = ConditionVariable.new
 *
 *    a = Thread.new {
 *       mutex.synchronize {
 *         # Thread 'a' now needs the resource
 *         resource.wait(mutex)
 *         # 'a' can now have the resource
 *       }
 *    }
 *
 *    b = Thread.new {
 *       mutex.synchronize {
 *         # Thread 'b' has finished using the resource
 *         resource.signal
 *       }
 *    }
 */

/*
 * Document-method: ConditionVariable::new
 *
 * Creates a new condition variable instance.
 */

static VALUE
rb_condvar_initialize(VALUE self)
{
    RSTRUCT_SET(self, CONDVAR_WAITERS, ary_buf_new());
    return self;
}

struct sleep_call {
    VALUE mutex;
    VALUE timeout;
};

static ID id_sleep;

static VALUE
do_sleep(VALUE args)
{
    struct sleep_call *p = (struct sleep_call *)args;
    return rb_funcall2(p->mutex, id_sleep, 1, &p->timeout);
}

static VALUE
delete_current_thread(VALUE ary)
{
    return rb_ary_delete(ary, rb_thread_current());
}

/*
 * Document-method: ConditionVariable#wait
 * call-seq: wait(mutex, timeout=nil)
 *
 * Releases the lock held in +mutex+ and waits; reacquires the lock on wakeup.
 *
 * If +timeout+ is given, this method returns after +timeout+ seconds passed,
 * even if no other thread doesn't signal.
 */

static VALUE
rb_condvar_wait(int argc, VALUE *argv, VALUE self)
{
    VALUE waiters = GET_CONDVAR_WAITERS(self);
    VALUE mutex, timeout;
    struct sleep_call args;

    rb_scan_args(argc, argv, "11", &mutex, &timeout);

    args.mutex   = mutex;
    args.timeout = timeout;
    rb_ary_push(waiters, rb_thread_current());
    rb_ensure(do_sleep, (VALUE)&args, delete_current_thread, waiters);

    return self;
}

/*
 * Document-method: ConditionVariable#signal
 *
 * Wakes up the first thread in line waiting for this lock.
 */

static VALUE
rb_condvar_signal(VALUE self)
{
    wakeup_first_thread(GET_CONDVAR_WAITERS(self));
    return self;
}

/*
 * Document-method: ConditionVariable#broadcast
 *
 * Wakes up all threads waiting for this lock.
 */

static VALUE
rb_condvar_broadcast(VALUE self)
{
    wakeup_all_threads(GET_CONDVAR_WAITERS(self));
    return self;
}

/* :nodoc: */
static VALUE
undumpable(VALUE obj)
{
    rb_raise(rb_eTypeError, "can't dump %"PRIsVALUE, rb_obj_class(obj));
    UNREACHABLE;
}

static void
Init_thread_sync(void)
{
#if 0
    rb_cConditionVariable = rb_define_class("ConditionVariable", rb_cObject); /* teach rdoc ConditionVariable */
    rb_cQueue = rb_define_class("Queue", rb_cObject); /* teach rdoc Queue */
    rb_cSizedQueue = rb_define_class("SizedQueue", rb_cObject); /* teach rdoc SizedQueue */
#endif

    /* Mutex */
    rb_cMutex = rb_define_class_under(rb_cThread, "Mutex", rb_cObject);
    rb_define_alloc_func(rb_cMutex, mutex_alloc);
    rb_define_method(rb_cMutex, "initialize", mutex_initialize, 0);
    rb_define_method(rb_cMutex, "locked?", rb_mutex_locked_p, 0);
    rb_define_method(rb_cMutex, "try_lock", rb_mutex_trylock, 0);
    rb_define_method(rb_cMutex, "lock", rb_mutex_lock, 0);
    rb_define_method(rb_cMutex, "unlock", rb_mutex_unlock, 0);
    rb_define_method(rb_cMutex, "sleep", mutex_sleep, -1);
    rb_define_method(rb_cMutex, "synchronize", rb_mutex_synchronize_m, 0);
    rb_define_method(rb_cMutex, "owned?", rb_mutex_owned_p, 0);

    /* Queue */
    rb_cQueue = rb_struct_define_without_accessor_under(
        rb_cThread,
        "Queue", rb_cObject, rb_struct_alloc_noinit,
        "que", "waiters", NULL);

    rb_eClosedQueueError = rb_define_class("ClosedQueueError", rb_eStopIteration);

    rb_define_method(rb_cQueue, "initialize", rb_queue_initialize, 0);
    rb_undef_method(rb_cQueue, "initialize_copy");
    rb_define_method(rb_cQueue, "marshal_dump", undumpable, 0);
    rb_define_method(rb_cQueue, "close", rb_queue_close, 0);
    rb_define_method(rb_cQueue, "closed?", rb_queue_closed_p, 0);
    rb_define_method(rb_cQueue, "push", rb_queue_push, 1);
    rb_define_method(rb_cQueue, "pop", rb_queue_pop, -1);
    rb_define_method(rb_cQueue, "empty?", rb_queue_empty_p, 0);
    rb_define_method(rb_cQueue, "clear", rb_queue_clear, 0);
    rb_define_method(rb_cQueue, "length", rb_queue_length, 0);
    rb_define_method(rb_cQueue, "num_waiting", rb_queue_num_waiting, 0);

    rb_define_alias(rb_cQueue, "enq", "push");    /* Alias for #push. */
    rb_define_alias(rb_cQueue, "<<", "push");     /* Alias for #push. */
    rb_define_alias(rb_cQueue, "deq", "pop");     /* Alias for #pop. */
    rb_define_alias(rb_cQueue, "shift", "pop");   /* Alias for #pop. */
    rb_define_alias(rb_cQueue, "size", "length"); /* Alias for #length. */

    rb_cSizedQueue = rb_struct_define_without_accessor_under(
        rb_cThread,
        "SizedQueue", rb_cQueue, rb_struct_alloc_noinit,
        "que", "waiters", "queue_waiters", "size", NULL);

    rb_define_method(rb_cSizedQueue, "initialize", rb_szqueue_initialize, 1);
    rb_define_method(rb_cSizedQueue, "close", rb_szqueue_close, 0);
    rb_define_method(rb_cSizedQueue, "max", rb_szqueue_max_get, 0);
    rb_define_method(rb_cSizedQueue, "max=", rb_szqueue_max_set, 1);
    rb_define_method(rb_cSizedQueue, "push", rb_szqueue_push, -1);
    rb_define_method(rb_cSizedQueue, "pop", rb_szqueue_pop, -1);
    rb_define_method(rb_cSizedQueue, "clear", rb_szqueue_clear, 0);
    rb_define_method(rb_cSizedQueue, "num_waiting", rb_szqueue_num_waiting, 0);

    rb_define_alias(rb_cSizedQueue, "enq", "push");  /* Alias for #push. */
    rb_define_alias(rb_cSizedQueue, "<<", "push");   /* Alias for #push. */
    rb_define_alias(rb_cSizedQueue, "deq", "pop");   /* Alias for #pop. */
    rb_define_alias(rb_cSizedQueue, "shift", "pop"); /* Alias for #pop. */

    /* CVar */
    rb_cConditionVariable = rb_struct_define_without_accessor_under(
        rb_cThread,
        "ConditionVariable", rb_cObject, rb_struct_alloc_noinit,
        "waiters", NULL);

    id_sleep = rb_intern("sleep");

    rb_define_method(rb_cConditionVariable, "initialize", rb_condvar_initialize, 0);
    rb_undef_method(rb_cConditionVariable, "initialize_copy");
    rb_define_method(rb_cConditionVariable, "marshal_dump", undumpable, 0);
    rb_define_method(rb_cConditionVariable, "wait", rb_condvar_wait, -1);
    rb_define_method(rb_cConditionVariable, "signal", rb_condvar_signal, 0);
    rb_define_method(rb_cConditionVariable, "broadcast", rb_condvar_broadcast, 0);

#define ALIAS_GLOBAL_CONST(name) \
    rb_define_const(rb_cObject, #name, rb_c##name)

    ALIAS_GLOBAL_CONST(Mutex);
    ALIAS_GLOBAL_CONST(Queue);
    ALIAS_GLOBAL_CONST(SizedQueue);
    ALIAS_GLOBAL_CONST(ConditionVariable);
    rb_provide("thread.rb");
}
/* */