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 * sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */

#include "uv-common.h"

#if !defined(_WIN32)
# include "unix/internal.h"
#endif

#include <stdlib.h>

#define MAX_THREADPOOL_SIZE 128

static uv_once_t once = UV_ONCE_INIT;
static uv_cond_t cond;
static uv_mutex_t mutex;
static unsigned int idle_threads;
static unsigned int slow_io_work_running;
static unsigned int nthreads;
static uv_thread_t* threads;
static uv_thread_t default_threads[4];
static QUEUE exit_message;
static QUEUE wq;
static QUEUE run_slow_work_message;
static QUEUE slow_io_pending_wq;

static unsigned int slow_work_thread_threshold(void) {
  return (nthreads + 1) / 2;
}

static void uv__cancelled(struct uv__work* w) {
  abort();
}


/* To avoid deadlock with uv_cancel() it's crucial that the worker
 * never holds the global mutex and the loop-local mutex at the same time.
 */
static void worker(void* arg) {
  struct uv__work* w;
  QUEUE* q;
  int is_slow_work;

  uv_sem_post((uv_sem_t*) arg);
  arg = NULL;

  uv_mutex_lock(&mutex);
  for (;;) {
    /* `mutex` should always be locked at this point. */

    /* Keep waiting while either no work is present or only slow I/O
       and we're at the threshold for that. */
    while (QUEUE_EMPTY(&wq) ||
           (QUEUE_HEAD(&wq) == &run_slow_work_message &&
            QUEUE_NEXT(&run_slow_work_message) == &wq &&
            slow_io_work_running >= slow_work_thread_threshold())) {
      idle_threads += 1;
      uv_cond_wait(&cond, &mutex);
      idle_threads -= 1;
    }

    q = QUEUE_HEAD(&wq);
    if (q == &exit_message) {
      uv_cond_signal(&cond);
      uv_mutex_unlock(&mutex);
      break;
    }

    QUEUE_REMOVE(q);
    QUEUE_INIT(q);  /* Signal uv_cancel() that the work req is executing. */

    is_slow_work = 0;
    if (q == &run_slow_work_message) {
      /* If we're at the slow I/O threshold, re-schedule until after all
         other work in the queue is done. */
      if (slow_io_work_running >= slow_work_thread_threshold()) {
        QUEUE_INSERT_TAIL(&wq, q);
        continue;
      }

      /* If we encountered a request to run slow I/O work but there is none
         to run, that means it's cancelled => Start over. */
      if (QUEUE_EMPTY(&slow_io_pending_wq))
        continue;

      is_slow_work = 1;
      slow_io_work_running++;

      q = QUEUE_HEAD(&slow_io_pending_wq);
      QUEUE_REMOVE(q);
      QUEUE_INIT(q);

      /* If there is more slow I/O work, schedule it to be run as well. */
      if (!QUEUE_EMPTY(&slow_io_pending_wq)) {
        QUEUE_INSERT_TAIL(&wq, &run_slow_work_message);
        if (idle_threads > 0)
          uv_cond_signal(&cond);
      }
    }

    uv_mutex_unlock(&mutex);

    w = QUEUE_DATA(q, struct uv__work, wq);
    w->work(w);

    uv_mutex_lock(&w->loop->wq_mutex);
    w->work = NULL;  /* Signal uv_cancel() that the work req is done
                        executing. */
    QUEUE_INSERT_TAIL(&w->loop->wq, &w->wq);