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libsimple: Implement condvars
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src/libsimple/include/libsimple/lock.h
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src/libsimple/include/libsimple/lock.h
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bool libsimple_rwlock_try_lock_write(libsimple_rwlock_t* rwlock);
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void libsimple_rwlock_unlock_write(libsimple_rwlock_t* rwlock);
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//
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// condvar
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//
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typedef struct libsimple_condvar {
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uint32_t state;
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} libsimple_condvar_t;
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#define LIBSIMPLE_CONDVAR_INITIALIZER {0}
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LIBSIMPLE_INLINE
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static void libsimple_condvar_init(libsimple_condvar_t* condvar) {
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condvar->state = 0;
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};
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// NOTE: the same lock must be used for all operations with a condvar.
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// the only reason we don't just store a pointer to the lock in the condvar
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// is so that condvars can be initialized statically.
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void libsimple_condvar_wait(libsimple_condvar_t* condvar, libsimple_lock_t* lock);
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void libsimple_condvar_notify_one(libsimple_condvar_t* condvar, libsimple_lock_t* lock);
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void libsimple_condvar_notify_all(libsimple_condvar_t* condvar, libsimple_lock_t* lock);
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LIBSIMPLE_DECLARATIONS_END;
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#endif // _LIBSIMPLE_LOCK_H_
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src/libsimple/src/lock.c
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src/libsimple/src/lock.c
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#define FUTEX_WAIT 0
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#define FUTEX_WAKE 1
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#define FUTEX_REQUEUE 3
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#define FUTEX_WAIT_BITSET 9
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#define FUTEX_WAKE_BITSET 10
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#define FUTEX_PRIVATE_FLAG 128
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#if LIBSIMPLE_DARLING
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#define linux_futex __linux_futex_reterr
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#else // !LIBSIMPLE_DARLING
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static void linux_futex(int* uaddr, int op, int val, const struct timespec* timeout, int* uaddr2, int val3) {
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static int linux_futex(int* uaddr, int op, int val, const struct timespec* timeout, int* uaddr2, int val3) {
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#if LIBSIMPLE_LINUX
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syscall(SYS_futex, uaddr, op, val, timeout, uaddr2, val3);
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return syscall(SYS_futex, uaddr, op, val, timeout, uaddr2, val3);
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#else
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#error linux_futex not implemented for this platform
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#endif
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}
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libsimple_lock_debug("lock acquired");
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};
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// based on Mutex::lock_pessimistic from https://github.com/bugaevc/lets-write-sync-primitives/blob/master/src/mutex.cpp
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//
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// this is used by condvars for locking the lock after waking up
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static void libsimple_lock_lock_slow(libsimple_lock_t* _lock) {
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libsimple_lock_internal_t* lock = (libsimple_lock_internal_t*)_lock;
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// this path assumes that the lock is contended
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uint32_t prev = atomic_exchange_explicit(&lock->state, libsimple_lock_state_locked_contended, memory_order_acquire);
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while (prev != libsimple_lock_state_unlocked) {
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linux_futex((int*)&lock->state, FUTEX_WAIT | FUTEX_PRIVATE_FLAG, libsimple_lock_state_locked_contended, NULL, 0, 0);
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prev = atomic_exchange_explicit(&lock->state, libsimple_lock_state_locked_contended, memory_order_acquire);
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}
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};
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void libsimple_lock_unlock(libsimple_lock_t* _lock) {
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linux_futex((int*)&rwlock->state, FUTEX_WAKE_BITSET | FUTEX_PRIVATE_FLAG, 1, NULL, NULL, libsimple_rwlock_bit_writer);
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}
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};
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//
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// libsimple_condvar
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//
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// based on https://github.com/bugaevc/lets-write-sync-primitives/blob/master/src/condvar.cpp
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//
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typedef struct libsimple_condvar_internal {
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_Atomic uint32_t state;
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} libsimple_condvar_internal_t;
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enum libsimple_condvar_bits {
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libsimple_condvar_bit_need_to_wake_one = 1 << 0,
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libsimple_condvar_bit_need_to_wake_all = 1 << 1,
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libsimple_condvar_bit_increment = 1 << 2,
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};
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void libsimple_condvar_wait(libsimple_condvar_t* _condvar, libsimple_lock_t* lock) {
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libsimple_condvar_internal_t* condvar = (void*)_condvar;
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uint32_t state2 = atomic_fetch_or_explicit(&condvar->state, libsimple_condvar_bit_need_to_wake_all | libsimple_condvar_bit_need_to_wake_one, memory_order_relaxed) | libsimple_condvar_bit_need_to_wake_all | libsimple_condvar_bit_need_to_wake_one;
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libsimple_lock_unlock(lock);
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linux_futex((int*)&condvar->state, FUTEX_WAIT | FUTEX_PRIVATE_FLAG, state2, NULL, NULL, 0);
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libsimple_lock_lock_slow(lock);
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};
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void libsimple_condvar_notify_one(libsimple_condvar_t* _condvar, libsimple_lock_t* lock) {
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libsimple_condvar_internal_t* condvar = (void*)_condvar;
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uint32_t state2 = atomic_fetch_add_explicit(&condvar->state, libsimple_condvar_bit_increment, memory_order_relaxed) + libsimple_condvar_bit_increment;
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int woken;
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if ((state2 & libsimple_condvar_bit_need_to_wake_one) == 0) {
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return;
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}
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state2 = atomic_fetch_and_explicit(&condvar->state, ~libsimple_condvar_bit_need_to_wake_one, memory_order_relaxed);
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if ((state2 & libsimple_condvar_bit_need_to_wake_one) == 0) {
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return;
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}
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woken = linux_futex((int*)&condvar->state, FUTEX_WAKE | FUTEX_PRIVATE_FLAG, 1, NULL, NULL, 0);
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if (woken > 0) {
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atomic_fetch_or_explicit(&condvar->state, libsimple_condvar_bit_need_to_wake_one, memory_order_relaxed);
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}
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};
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void libsimple_condvar_notify_all(libsimple_condvar_t* _condvar, libsimple_lock_t* _lock) {
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libsimple_condvar_internal_t* condvar = (void*)_condvar;
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libsimple_lock_internal_t* lock = (void*)_lock;
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uint32_t state2 = atomic_fetch_add_explicit(&condvar->state, libsimple_condvar_bit_increment, memory_order_relaxed) + libsimple_condvar_bit_increment;
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if ((state2 & libsimple_condvar_bit_need_to_wake_all) == 0) {
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return;
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}
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atomic_fetch_and_explicit(&condvar->state, ~(libsimple_condvar_bit_need_to_wake_all | libsimple_condvar_bit_need_to_wake_one), memory_order_relaxed);
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linux_futex((int*)&condvar->state, FUTEX_REQUEUE | FUTEX_PRIVATE_FLAG, 1, /* actually `uint32_t val2`, not timeout */ (void*)INT_MAX, (int*)&lock->state, 0);
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};