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// Shared mutex can be used in shared memory for interprocess
// synchronization.
//
#ifndef KIT_SHARED_MUTEX_H
#define KIT_SHARED_MUTEX_H
#include "atomic.h"
#include "threads.h"
#include <assert.h>
#include <string.h>
#ifdef __cplusplus
extern "C" {
#endif
#if defined(__GNUC__) || defined(__clang__)
# pragma GCC diagnostic push
# pragma GCC diagnostic ignored "-Wunused-function"
# pragma GCC diagnostic ignored "-Wunknown-pragmas"
# pragma GCC push_options
# pragma GCC optimize("O3")
#endif
enum {
KIT_SHARED_MUTEX_READY = 1,
KIT_SHARED_MUTEX_LOCKED,
KIT_SHARED_MUTEX_WRITER
};
typedef union {
struct {
i8 _Atomic state;
i32 readers;
};
struct {
u8 _pad[16];
};
} kit_shared_mutex_t;
static void kit_shared_mutex_init(kit_shared_mutex_t *m) {
assert(m != NULL);
memset(m, 0, sizeof *m);
atomic_store_explicit(&m->state, KIT_SHARED_MUTEX_READY,
memory_order_relaxed);
}
static i8 kit_shared_try_lock(kit_shared_mutex_t *m) {
assert(m != NULL);
for (;;) {
i8 prev_state = KIT_SHARED_MUTEX_READY;
if (atomic_compare_exchange_strong_explicit(
&m->state, &prev_state, KIT_SHARED_MUTEX_LOCKED,
memory_order_seq_cst, memory_order_seq_cst))
break;
if (prev_state == KIT_SHARED_MUTEX_WRITER)
return 0;
// FIXME
// Check performance
thrd_yield();
}
assert(m->readers >= 0);
++m->readers;
i8 prev_state = KIT_SHARED_MUTEX_LOCKED;
if (!atomic_compare_exchange_strong_explicit(
&m->state, &prev_state, KIT_SHARED_MUTEX_READY,
memory_order_seq_cst, memory_order_seq_cst))
assert(0);
return 1;
}
static void kit_shared_lock(kit_shared_mutex_t *m) {
assert(m != NULL);
while (!kit_shared_try_lock(m))
// FIXME
// Check performance
thrd_yield();
}
static void kit_shared_unlock(kit_shared_mutex_t *m) {
assert(m != NULL);
for (;;) {
i8 prev_state = KIT_SHARED_MUTEX_READY;
if (atomic_compare_exchange_strong_explicit(
&m->state, &prev_state, KIT_SHARED_MUTEX_LOCKED,
memory_order_seq_cst, memory_order_seq_cst))
break;
// FIXME
// Check performance
thrd_yield();
}
assert(m->readers > 0);
m->readers--;
i8 prev_state = KIT_SHARED_MUTEX_LOCKED;
if (!atomic_compare_exchange_strong_explicit(
&m->state, &prev_state, KIT_SHARED_MUTEX_READY,
memory_order_seq_cst, memory_order_seq_cst))
assert(0);
}
static i8 kit_unique_try_lock(kit_shared_mutex_t *m) {
assert(m != NULL);
i8 prev_state = KIT_SHARED_MUTEX_READY;
if (!atomic_compare_exchange_strong_explicit(
&m->state, &prev_state, KIT_SHARED_MUTEX_WRITER,
memory_order_seq_cst, memory_order_seq_cst))
return 0;
i8 is_locked = (m->readers == 0);
prev_state = KIT_SHARED_MUTEX_WRITER;
if (!is_locked &&
!atomic_compare_exchange_strong_explicit(
&m->state, &prev_state, KIT_SHARED_MUTEX_READY,
memory_order_seq_cst, memory_order_seq_cst))
assert(0);
return is_locked;
}
static void kit_unique_lock(kit_shared_mutex_t *m) {
assert(m != NULL);
while (!kit_unique_try_lock(m))
// FIXME
// Check performance
thrd_yield();
}
static void kit_unique_unlock(kit_shared_mutex_t *m) {
assert(m != NULL);
i8 prev_state = KIT_SHARED_MUTEX_WRITER;
if (!atomic_compare_exchange_strong_explicit(
&m->state, &prev_state, KIT_SHARED_MUTEX_READY,
memory_order_seq_cst, memory_order_seq_cst))
assert(0);
}
#if defined(__GNUC__) || defined(__clang__)
# pragma GCC pop_options
# pragma GCC diagnostic pop
#endif
#ifdef __cplusplus
}
#endif
#define shared_mutex_t kit_shared_mutex_t
#define shared_mutex_init kit_shared_mutex_init
#define shared_try_lock kit_shared_try_lock
#define shared_lock kit_shared_lock
#define shared_unlock kit_shared_unlock
#define unique_try_lock kit_unique_try_lock
#define unique_lock kit_unique_lock
#define unique_unlock kit_unique_unlock
#define shared_mutex_init kit_shared_mutex_init
#define shared_try_lock kit_shared_try_lock
#define shared_lock kit_shared_lock
#define shared_unlock kit_shared_unlock
#define unique_try_lock kit_unique_try_lock
#define unique_lock kit_unique_lock
#define unique_unlock kit_unique_unlock
#endif
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