#ifndef _SPINLOCK_H #define _SPINLOCK_H #include #ifdef DEBUG #define DEBUG_SPINLOCKS #endif // DEBUG #if defined DEBUG_SPINLOCKS && defined IN_SHIM #define DEBUG_SPINLOCKS_SHIM #include pid_t shim_do_gettid(void); #endif // defined DEBUG_SPINLOCKS && defined IN_SHIM typedef struct { int lock; #ifdef DEBUG_SPINLOCKS_SHIM pid_t owner; #endif // DEBUG_SPINLOCKS_SHIM } spinlock_t; /* Use this to initialize spinlocks with *static* storage duration. * According to C standard, there only guarantee we have is that this initialization will happen * before main, which by itself is not enough (such store might not be visible before fist lock * acquire). Fortunately on gcc global zeroed variables will just end up in .bss - zeroed memory * mapped during process creation, hence we are fine. * * Rest of the struct is zeroed implicitly, hence no need for ifdef here. */ #define INIT_SPINLOCK_UNLOCKED { .lock = 0 } #ifdef DEBUG_SPINLOCKS_SHIM static inline void debug_spinlock_take_ownership(spinlock_t* lock) { __atomic_store_n(&lock->owner, shim_do_gettid(), __ATOMIC_RELAXED); } static inline void debug_spinlock_giveup_ownership(spinlock_t* lock) { __atomic_store_n(&lock->owner, 0, __ATOMIC_RELAXED); } #else static inline void debug_spinlock_take_ownership(spinlock_t* lock) { __UNUSED(lock); } static inline void debug_spinlock_giveup_ownership(spinlock_t* lock) { __UNUSED(lock); } #endif // DEBUG_SPINLOCKS_SHIM /* Use this to initialize spinlocks with *dynamic* storage duration. */ static inline void spinlock_init(spinlock_t *lock) { debug_spinlock_giveup_ownership(lock); __atomic_store_n(&lock->lock, 0, __ATOMIC_RELAXED); } /* Returns 0 if taking the lock succeded, 1 if it was already taken */ static inline int spinlock_trylock(spinlock_t* lock) { if (__atomic_exchange_n(&lock->lock, 1, __ATOMIC_ACQUIRE) == 0) { debug_spinlock_take_ownership(lock); return 0; } return 1; } static inline void spinlock_lock(spinlock_t* lock) { int val; /* First check if lock is already free. */ if (__atomic_exchange_n(&lock->lock, 1, __ATOMIC_ACQUIRE) == 0) { goto out; } do { /* This check imposes no inter-thread ordering, thus does not slow other threads. */ while (__atomic_load_n(&lock->lock, __ATOMIC_RELAXED) != 0) { __asm__ volatile ("pause"); } /* Seen lock as free, check if it still is, this time with acquire semantics (but only * if we really take it). */ val = 0; } while (!__atomic_compare_exchange_n(&lock->lock, &val, 1, 1, __ATOMIC_ACQUIRE, __ATOMIC_RELAXED)); out: debug_spinlock_take_ownership(lock); } static inline void spinlock_unlock(spinlock_t* lock) { debug_spinlock_giveup_ownership(lock); __atomic_store_n(&lock->lock, 0, __ATOMIC_RELEASE); } #ifdef DEBUG_SPINLOCKS static inline bool _spinlock_is_locked(spinlock_t* lock) { return __atomic_load_n(&lock->lock, __ATOMIC_SEQ_CST) != 0; } #ifdef DEBUG_SPINLOCKS_SHIM static inline bool spinlock_is_locked(spinlock_t* lock) { if (!_spinlock_is_locked(lock)) { return false; } pid_t owner = __atomic_load_n(&lock->owner, __ATOMIC_RELAXED); if (owner != shim_do_gettid()) { debug("Unexpected lock ownership: owned by: %d, checked in: %d", owner, shim_do_gettid()); return false; } return true; } #else static inline bool spinlock_is_locked(spinlock_t* lock) { return _spinlock_is_locked(lock); } #endif // DEBUG_SPINLOCKS_SHIM #endif // DEBUG_SPINLOCKS #endif // _SPINLOCK_H