text: /*
   * Copyright (c) 2018 Apple Inc. All rights reserved.
   *
   * @APPLE_APACHE_LICENSE_HEADER_START@
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   *
   * @APPLE_APACHE_LICENSE_HEADER_END@
   */
  
  #include "internal.h"
  
  DISPATCH_NOINLINE
  static void *
  __DISPATCH_WAIT_FOR_ENQUEUER__(void **ptr, void **tailp)
  {
  	unsigned int spins = 0;
  	void *value;
  	while ((value = os_atomic_load(ptr, relaxed)) == NULL) {
  		/* ptr == &prev->do_next */
  		_dispatch_yield_to_enqueuer(tailp, ++spins);
  	}
  	return value;
  }
  
  void *
  _dispatch_wait_for_enqueuer(void **ptr, void **tailp)
  {
  #if !DISPATCH_HW_CONFIG_UP
  #if defined(__arm__) || defined(__arm64__)
  	int spins = DISPATCH_WAIT_SPINS_WFE;
  	void *value;
  	while (unlikely(spins-- > 0)) {
  		if (likely(value = __builtin_arm_ldrex(ptr))) {
  			__builtin_arm_clrex();
  			return value;
  		}
  		__builtin_arm_wfe();
  	}
  #else
  	int spins = DISPATCH_WAIT_SPINS;
  	void *value;
  	while (unlikely(spins-- > 0)) {
  		if (likely(value = os_atomic_load(ptr, relaxed))) {
  			return value;
  		}
  		dispatch_hardware_pause();
  	}
  #endif
  #endif // DISPATCH_HW_CONFIG_UP
  	return __DISPATCH_WAIT_FOR_ENQUEUER__(ptr, tailp);
  }
  