| /* |
| * 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) |
| { |
| int spins = 0; |
| void *value; |
| while ((value = os_atomic_load(ptr, relaxed)) == NULL) { |
| _dispatch_preemption_yield(++spins); |
| } |
| return value; |
| } |
| |
| void * |
| _dispatch_wait_for_enqueuer(void **ptr) |
| { |
| #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); |
| } |