blob: f359f4eb78970bca91d9707a1b983d0daf0a5976 [file] [log] [blame]
// Copyright 2021 gRPC authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include <grpc/support/port_platform.h>
#include "src/core/lib/promise/activity.h"
#include <stddef.h>
#include "src/core/lib/gprpp/atomic_utils.h"
namespace grpc_core {
///////////////////////////////////////////////////////////////////////////////
// GLOBALS
GPR_THREAD_LOCAL(Activity*) Activity::g_current_activity_{nullptr};
Waker::Unwakeable Waker::unwakeable_;
namespace promise_detail {
///////////////////////////////////////////////////////////////////////////////
// HELPER TYPES
// Weak handle to an Activity.
// Handle can persist while Activity goes away.
class FreestandingActivity::Handle final : public Wakeable {
public:
explicit Handle(FreestandingActivity* activity) : activity_(activity) {}
// Ref the Handle (not the activity).
void Ref() { refs_.fetch_add(1, std::memory_order_relaxed); }
// Activity is going away... drop its reference and sever the connection back.
void DropActivity() ABSL_LOCKS_EXCLUDED(mu_) {
mu_.Lock();
GPR_ASSERT(activity_ != nullptr);
activity_ = nullptr;
mu_.Unlock();
Unref();
}
// Activity needs to wake up (if it still exists!) - wake it up, and drop the
// ref that was kept for this handle.
void Wakeup() override ABSL_LOCKS_EXCLUDED(mu_) {
mu_.Lock();
// Note that activity refcount can drop to zero, but we could win the lock
// against DropActivity, so we need to only increase activities refcount if
// it is non-zero.
if (activity_ && activity_->RefIfNonzero()) {
FreestandingActivity* activity = activity_;
mu_.Unlock();
// Activity still exists and we have a reference: wake it up, which will
// drop the ref.
activity->Wakeup();
} else {
// Could not get the activity - it's either gone or going. No need to wake
// it up!
mu_.Unlock();
}
// Drop the ref to the handle (we have one ref = one wakeup semantics).
Unref();
}
void Drop() override { Unref(); }
private:
// Unref the Handle (not the activity).
void Unref() {
if (1 == refs_.fetch_sub(1, std::memory_order_acq_rel)) {
delete this;
}
}
// Two initial refs: one for the waiter that caused instantiation, one for the
// activity.
std::atomic<size_t> refs_{2};
Mutex mu_ ABSL_ACQUIRED_AFTER(activity_->mu_);
FreestandingActivity* activity_ ABSL_GUARDED_BY(mu_);
};
///////////////////////////////////////////////////////////////////////////////
// ACTIVITY IMPLEMENTATION
bool FreestandingActivity::RefIfNonzero() { return IncrementIfNonzero(&refs_); }
FreestandingActivity::Handle* FreestandingActivity::RefHandle() {
if (handle_ == nullptr) {
// No handle created yet - construct it and return it.
handle_ = new Handle(this);
return handle_;
} else {
// Already had to create a handle, ref & return it.
handle_->Ref();
return handle_;
}
}
void FreestandingActivity::DropHandle() {
handle_->DropActivity();
handle_ = nullptr;
}
Waker FreestandingActivity::MakeNonOwningWaker() {
mu_.AssertHeld();
return Waker(RefHandle());
}
} // namespace promise_detail
} // namespace grpc_core