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/*
* Copyright (c) 2020, the SerenityOS developers.
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <Kernel/Debug.h>
#include <Kernel/FutexQueue.h>
#include <Kernel/Thread.h>
namespace Kernel {
FutexQueue::FutexQueue() = default;
FutexQueue::~FutexQueue() = default;
bool FutexQueue::should_add_blocker(Thread::Blocker& b, void*)
{
VERIFY(m_lock.is_locked());
VERIFY(b.blocker_type() == Thread::Blocker::Type::Futex);
VERIFY(m_imminent_waits > 0);
m_imminent_waits--;
if (m_was_removed) {
dbgln_if(FUTEXQUEUE_DEBUG, "FutexQueue @ {}: should not block thread {}: was removed", this, b.thread());
return false;
}
dbgln_if(FUTEXQUEUE_DEBUG, "FutexQueue @ {}: should block thread {}", this, b.thread());
return true;
}
u32 FutexQueue::wake_n_requeue(u32 wake_count, Function<FutexQueue*()> const& get_target_queue, u32 requeue_count, bool& is_empty, bool& is_empty_target)
{
is_empty_target = false;
SpinlockLocker lock(m_lock);
dbgln_if(FUTEXQUEUE_DEBUG, "FutexQueue @ {}: wake_n_requeue({}, {})", this, wake_count, requeue_count);
u32 did_wake = 0, did_requeue = 0;
unblock_all_blockers_whose_conditions_are_met_locked([&](Thread::Blocker& b, void*, bool& stop_iterating) {
VERIFY(b.blocker_type() == Thread::Blocker::Type::Futex);
auto& blocker = static_cast<Thread::FutexBlocker&>(b);
dbgln_if(FUTEXQUEUE_DEBUG, "FutexQueue @ {}: wake_n_requeue unblocking {}", this, blocker.thread());
VERIFY(did_wake < wake_count);
if (blocker.unblock()) {
if (++did_wake >= wake_count)
stop_iterating = true;
return true;
}
return false;
});
is_empty = is_empty_and_no_imminent_waits_locked();
if (requeue_count > 0) {
auto blockers_to_requeue = do_take_blockers(requeue_count);
if (!blockers_to_requeue.is_empty()) {
if (auto* target_futex_queue = get_target_queue()) {
dbgln_if(FUTEXQUEUE_DEBUG, "FutexQueue @ {}: wake_n_requeue requeueing {} blockers to {}", this, blockers_to_requeue.size(), target_futex_queue);
// While still holding m_lock, notify each blocker
for (auto& info : blockers_to_requeue) {
VERIFY(info.blocker->blocker_type() == Thread::Blocker::Type::Futex);
auto& blocker = *static_cast<Thread::FutexBlocker*>(info.blocker);
blocker.begin_requeue();
}
lock.unlock();
did_requeue = blockers_to_requeue.size();
SpinlockLocker target_lock(target_futex_queue->m_lock);
// Now that we have the lock of the target, append the blockers
// and notify them that they completed the move
for (auto& info : blockers_to_requeue) {
VERIFY(info.blocker->blocker_type() == Thread::Blocker::Type::Futex);
auto& blocker = *static_cast<Thread::FutexBlocker*>(info.blocker);
blocker.finish_requeue(*target_futex_queue);
}
target_futex_queue->do_append_blockers(move(blockers_to_requeue));
is_empty_target = target_futex_queue->is_empty_and_no_imminent_waits_locked();
} else {
dbgln_if(FUTEXQUEUE_DEBUG, "FutexQueue @ {}: wake_n_requeue could not get target queue to requeue {} blockers", this, blockers_to_requeue.size());
do_append_blockers(move(blockers_to_requeue));
}
}
}
return did_wake + did_requeue;
}
u32 FutexQueue::wake_n(u32 wake_count, Optional<u32> const& bitset, bool& is_empty)
{
if (wake_count == 0) {
is_empty = false;
return 0; // should we assert instead?
}
SpinlockLocker lock(m_lock);
dbgln_if(FUTEXQUEUE_DEBUG, "FutexQueue @ {}: wake_n({})", this, wake_count);
u32 did_wake = 0;
unblock_all_blockers_whose_conditions_are_met_locked([&](Thread::Blocker& b, void*, bool& stop_iterating) {
VERIFY(b.blocker_type() == Thread::Blocker::Type::Futex);
auto& blocker = static_cast<Thread::FutexBlocker&>(b);
dbgln_if(FUTEXQUEUE_DEBUG, "FutexQueue @ {}: wake_n unblocking {}", this, blocker.thread());
VERIFY(did_wake < wake_count);
if (bitset.has_value() ? blocker.unblock_bitset(bitset.value()) : blocker.unblock()) {
if (++did_wake >= wake_count)
stop_iterating = true;
return true;
}
return false;
});
is_empty = is_empty_and_no_imminent_waits_locked();
return did_wake;
}
u32 FutexQueue::wake_all(bool& is_empty)
{
SpinlockLocker lock(m_lock);
dbgln_if(FUTEXQUEUE_DEBUG, "FutexQueue @ {}: wake_all", this);
u32 did_wake = 0;
unblock_all_blockers_whose_conditions_are_met_locked([&](Thread::Blocker& b, void*, bool&) {
VERIFY(b.blocker_type() == Thread::Blocker::Type::Futex);
auto& blocker = static_cast<Thread::FutexBlocker&>(b);
dbgln_if(FUTEXQUEUE_DEBUG, "FutexQueue @ {}: wake_all unblocking {}", this, blocker.thread());
if (blocker.unblock(true)) {
did_wake++;
return true;
}
return false;
});
is_empty = is_empty_and_no_imminent_waits_locked();
return did_wake;
}
bool FutexQueue::is_empty_and_no_imminent_waits_locked()
{
return m_imminent_waits == 0 && is_empty_locked();
}
bool FutexQueue::queue_imminent_wait()
{
SpinlockLocker lock(m_lock);
if (m_was_removed)
return false;
m_imminent_waits++;
return true;
}
bool FutexQueue::try_remove()
{
SpinlockLocker lock(m_lock);
if (m_was_removed)
return false;
if (!is_empty_and_no_imminent_waits_locked())
return false;
m_was_removed = true;
return true;
}
}
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