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#include "stdafx.h"
#include "Sync.h"
#include "Thread.h"
#include "UThread.h"
namespace os {
Sema::Sema(nat count) : count(count) {}
Sema::~Sema() {}
void Sema::up() {
UThreadData *toWake = null;
{
util::Lock::L z(lock);
toWake = waiting.pop();
if (!toWake) {
// No thread to wake.
count++;
return;
}
}
// Wake the thread up. Note: We can not do that inside the lock. Otherwise, the thread might
// wake up before we have time to release the lock, which could cause us to crash if this
// semaphore was deallocated by the thread that we woke (a typical use case for semaphores).
toWake->owner()->wake(toWake);
}
void Sema::down() {
UThreadState *state = null;
{
util::Lock::L z(lock);
if (count > 0) {
count--;
return;
}
// Add us to the waiting queue.
if (!state)
state = UThreadState::current();
waiting.push(state->runningThread());
}
// Wait until we're woken up again.
state->wait();
}
/**
* Lock
*/
Lock::Lock() : sema(1) {}
Lock::~Lock() {}
Lock::L::L(Lock &l) : owner(l) {
owner.lock();
}
Lock::L::~L() {
owner.unlock();
}
void Lock::lock() {
sema.down();
}
void Lock::unlock() {
sema.up();
}
/**
* Event.
*/
Event::Event() : s(0) {}
Event::~Event() {
set();
}
void Event::set() {
atomicWrite(s, 1);
// Wake all threads. We need to be a bit careful here. We need to be aware of the situation
// where a woken thread could deallocate this event. As such, we must not hold the lock
// while waking the threads! We solve this by storing all threads in a separate, local, list
// and then waking them all.
InlineList<UThreadData> local;
{
util::Lock::L z(lock);
while (UThreadData *data = waiting.pop())
local.push(data);
}
// Now we can take our time and wake the threads.
while (UThreadData *toWake = local.pop())
toWake->owner()->wake(toWake);
}
void Event::clear() {
atomicWrite(s, 0);
}
bool Event::isSet() {
return atomicRead(s) == 1;
}
void Event::wait() {
if (atomicRead(s) == 1)
return;
// Wait...
UThreadState *state = null;
{
util::Lock::L z(lock);
// Add us to the waiting queue.
state = UThreadState::current();
waiting.push(state->runningThread());
}
// Wait until we're woken up again.
state->wait();
}
}
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