1 /* 2 * 3 * Copyright 2015 gRPC authors. 4 * 5 * Licensed under the Apache License, Version 2.0 (the "License"); 6 * you may not use this file except in compliance with the License. 7 * You may obtain a copy of the License at 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 11 * Unless required by applicable law or agreed to in writing, software 12 * distributed under the License is distributed on an "AS IS" BASIS, 13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 * See the License for the specific language governing permissions and 15 * limitations under the License. 16 * 17 */ 18 19 #ifndef GRPC_CORE_LIB_GPR_SPINLOCK_H 20 #define GRPC_CORE_LIB_GPR_SPINLOCK_H 21 22 #include <grpc/support/port_platform.h> 23 24 #include <grpc/support/atm.h> 25 26 // Simple spinlock. No backoff strategy, gpr_spinlock_lock is almost always 27 // a concurrency code smell. Code must _never_ block while holding a spinlock 28 // as this could lead to a deadlock under a cooperative multithreading model. 29 struct gpr_spinlock { 30 gpr_atm atm; 31 }; 32 #ifdef __cplusplus 33 #define GPR_SPINLOCK_INITIALIZER (gpr_spinlock{0}) 34 #else 35 #define GPR_SPINLOCK_INITIALIZER ((gpr_spinlock){0}) 36 #endif 37 #define GPR_SPINLOCK_STATIC_INITIALIZER \ 38 { 0 } 39 40 #define gpr_spinlock_trylock(lock) (gpr_atm_acq_cas(&(lock)->atm, 0, 1)) 41 #define gpr_spinlock_unlock(lock) (gpr_atm_rel_store(&(lock)->atm, 0)) 42 // Although the following code spins without any library or system calls, it 43 // still functions under cooperative multithreading. The principle is that 44 // the lock holder can't block, so it will be scheduled onto its system thread 45 // for the entire critical section. By the time another thread attempts a lock, 46 // it will either get it immediately or will be scheduled onto another system 47 // thread that is different from the current lockholder. There is no chance of 48 // waiting for a lockholder scheduled to the same system thread. 49 #define gpr_spinlock_lock(lock) \ 50 do { \ 51 } while (!gpr_spinlock_trylock((lock))) 52 53 #endif /* GRPC_CORE_LIB_GPR_SPINLOCK_H */ 54