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#include <stdio.h>
#include <stdbool.h>
#include <stdint.h>
#include <assert.h>
typedef uint32_t uint32;
typedef struct {
volatile uint32 value;
} pg_atomic_uint32;
#define AssertPointerAlignment(ptr, align) assert(((uintptr_t)(ptr) % (align)) == 0)
#define LW_EXCLUSIVE 1
#define LW_SHARED 2
#define LW_LOCK_MASK 0xF
#define LW_VAL_EXCLUSIVE 0x10
#define LW_VAL_SHARED 0x20
typedef struct {
pg_atomic_uint32 state;
#ifdef LOCK_DEBUG
void* owner;
#endif
} LWLock;
/* Atomic compare-and-exchange function */
static inline bool
pg_atomic_compare_exchange_u32_impl(volatile pg_atomic_uint32 *ptr,
uint32 *expected, uint32 newval)
{
unsigned char ret; // Use unsigned char for setz result
__asm__ __volatile__(
"lock\n\t"
"cmpxchgl %3, %2\n\t"
"setz %1"
: "=a" (*expected), "=q" (ret), "+m" (ptr->value)
: "r" (newval), "a" (*expected)
: "memory", "cc");
assert(1 == ret);
return (bool) ret;
}
static inline bool
pg_atomic_compare_exchange_u32(volatile pg_atomic_uint32 *ptr,
uint32 *expected, uint32 newval)
{
AssertPointerAlignment(ptr, 4);
AssertPointerAlignment(expected, 4);
return pg_atomic_compare_exchange_u32_impl(ptr, expected, newval);
}
/* Attempt to lock function */
static bool
LWLockAttemptLock(LWLock *lock, uint32 mode)
{
uint32 old_state;
//Assert(mode == LW_EXCLUSIVE || mode == LW_SHARED);
old_state = lock->state.value;
while (true)
{
uint32 desired_state;
bool lock_free;
desired_state = old_state;
if (mode == LW_EXCLUSIVE)
{
lock_free = (old_state & LW_LOCK_MASK) == 0;
if (lock_free)
desired_state += LW_VAL_EXCLUSIVE;
}
else
{
lock_free = (old_state & LW_VAL_EXCLUSIVE) == 0;
if (lock_free)
desired_state += LW_VAL_SHARED;
}
if (pg_atomic_compare_exchange_u32(&lock->state, &old_state, desired_state))
{
if (lock_free)
{
#ifdef LOCK_DEBUG
if (mode == LW_EXCLUSIVE)
lock->owner = (void*)1; // Simulating a lock owner for debug
#endif
return false;
}
else
return true;
}
}
}
int main() {
LWLock lock = {{0}}; // Initialize the lock
// Attempt to acquire an exclusive lock
if (!LWLockAttemptLock(&lock, LW_EXCLUSIVE)) {
printf("Acquired exclusive lock.\n");
} else {
printf("Failed to acquire exclusive lock.\n");
}
// Attempt to acquire a shared lock
if (!LWLockAttemptLock(&lock, LW_SHARED)) {
printf("Acquired shared lock.\n");
} else {
printf("Failed to acquire shared lock.\n");
}
return 0;
}
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