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_SRC_CORE_UTIL_SPINLOCK_H 20 #define GRPC_SRC_CORE_UTIL_SPINLOCK_H 21 22 #include <grpc/support/atm.h> 23 #include <grpc/support/port_platform.h> 24 25 // Simple spinlock. No backoff strategy, gpr_spinlock_lock is almost always 26 // a concurrency code smell. Code must _never_ block while holding a spinlock 27 // as this could lead to a deadlock under a cooperative multithreading model. 28 struct gpr_spinlock { 29 gpr_atm atm; 30 }; 31 #ifdef __cplusplus 32 #define GPR_SPINLOCK_INITIALIZER (gpr_spinlock{0}) 33 #else 34 #define GPR_SPINLOCK_INITIALIZER ((gpr_spinlock){0}) 35 #endif 36 #define GPR_SPINLOCK_STATIC_INITIALIZER {0} 37 38 #define gpr_spinlock_trylock(lock) (gpr_atm_acq_cas(&(lock)->atm, 0, 1)) 39 #define gpr_spinlock_unlock(lock) (gpr_atm_rel_store(&(lock)->atm, 0)) 40 // Although the following code spins without any library or system calls, it 41 // still functions under cooperative multithreading. The principle is that 42 // the lock holder can't block, so it will be scheduled onto its system thread 43 // for the entire critical section. By the time another thread attempts a lock, 44 // it will either get it immediately or will be scheduled onto another system 45 // thread that is different from the current lockholder. There is no chance of 46 // waiting for a lockholder scheduled to the same system thread. 47 #define gpr_spinlock_lock(lock) \ 48 do { \ 49 } while (!gpr_spinlock_trylock((lock))) 50 51 #endif // GRPC_SRC_CORE_UTIL_SPINLOCK_H 52