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AK: Add Atomic.h

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Use gcc built-in atomics
This commit is contained in:
Tom 2019-10-12 11:17:34 -06:00 • committed by Andreas Kling
parent 2530378f59
commit b0773a8ea6
6 changed files with 606 additions and 53 deletions
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34
Libraries/LibThread/Lock.h
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@ -4,22 +4,9 @@
#include <AK/Assertions.h>
#include <AK/Types.h>
#include <AK/Atomic.h>
#include <unistd.h>
#define memory_barrier() asm volatile("" :: \
: "memory")
static inline u32 CAS(volatile u32* mem, u32 newval, u32 oldval)
{
u32 ret;
asm volatile(
"cmpxchgl %2, %1"
: "=a"(ret), "+m"(*mem)
: "r"(newval), "0"(oldval)
: "cc", "memory");
return ret;
}
namespace LibThread {
class Lock {
@ -31,7 +18,7 @@ public:
void unlock();
private:
volatile u32 m_lock { 0 };
AK::Atomic<bool> m_lock { false };
u32 m_level { 0 };
int m_holder { -1 };
};
@ -55,15 +42,15 @@ private:
{
int tid = gettid();
for (;;) {
if (CAS(&m_lock, 1, 0) == 0) {
bool expected = false;
if (m_lock.compare_exchange_strong(expected, true, AK::memory_order_acq_rel)) {
if (m_holder == -1 || m_holder == tid) {
m_holder = tid;
++m_level;
memory_barrier();
m_lock = 0;
m_lock.store(false, AK::memory_order_release);
return;
}
m_lock = 0;
m_lock.store(false, AK::memory_order_release);
}
donate(m_holder);
}
@ -72,18 +59,17 @@ private:
inline void Lock::unlock()
{
for (;;) {
if (CAS(&m_lock, 1, 0) == 0) {
bool expected = false;
if (m_lock.compare_exchange_strong(expected, true, AK::memory_order_acq_rel)) {
ASSERT(m_holder == gettid());
ASSERT(m_level);
--m_level;
if (m_level) {
memory_barrier();
m_lock = 0;
m_lock.store(false, AK::memory_order_release);
return;
}
m_holder = -1;
memory_barrier();
m_lock = 0;
m_lock.store(false, AK::memory_order_release);
return;
}
donate(m_holder);