src/dawn/native/ExecutionQueue.cpp

// Copyright 2023 The Dawn & Tint Authors
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#include "dawn/native/ExecutionQueue.h"

#include <atomic>
#include <utility>
#include <vector>

#include "dawn/common/Atomic.h"

namespace dawn::native {

ExecutionSerial ExecutionQueueBase::GetPendingCommandSerial() const {
    return ExecutionSerial(mLastSubmittedSerial.load(std::memory_order_acquire) + 1);
}

ExecutionSerial ExecutionQueueBase::GetLastSubmittedCommandSerial() const {
    return ExecutionSerial(mLastSubmittedSerial.load(std::memory_order_acquire));
}

ExecutionSerial ExecutionQueueBase::GetCompletedCommandSerial() const {
    return ExecutionSerial(mCompletedSerial.load(std::memory_order_acquire));
}

MaybeError ExecutionQueueBase::CheckPassedSerials() {
    ExecutionSerial completedSerial;
    DAWN_TRY_ASSIGN(completedSerial, CheckAndUpdateCompletedSerials());

    DAWN_ASSERT(completedSerial <=
                ExecutionSerial(mLastSubmittedSerial.load(std::memory_order_acquire)));

    // Atomically set mCompletedSerial to completedSerial if completedSerial is larger.
    FetchMax(mCompletedSerial, uint64_t(completedSerial));

    // TODO(crbug.com/421945313): We should call |UpdateCompletedSerial| here also, but since some
    // backends rely on the device lock for safe use of |CheckAndUpdateCompletedSerials|, we
    // separate that call out for now.
    return {};
}

void ExecutionQueueBase::TrackSerialTask(ExecutionSerial serial, Task&& task) {
    if (serial <= GetCompletedCommandSerial()) {
        task();
        return;
    }
    mWaitingTasks->Enqueue(std::move(task), serial);
}

void ExecutionQueueBase::UpdateCompletedSerial(ExecutionSerial completedSerial) {
    // Atomically set mCompletedSerial to completedSerial if completedSerial is larger.
    FetchMax(mCompletedSerial, uint64_t(completedSerial));

    std::vector<Task> pending;
    mWaitingTasks.Use([&](auto tasks) {
        for (auto task : tasks->IterateUpTo(completedSerial)) {
            pending.push_back(std::move(task));
        }
        tasks->ClearUpTo(completedSerial);
    });
    for (auto task : pending) {
        task();
    }
}

MaybeError ExecutionQueueBase::EnsureCommandsFlushed(ExecutionSerial serial) {
    DAWN_ASSERT(serial <= GetPendingCommandSerial());
    if (serial > GetLastSubmittedCommandSerial()) {
        ForceEventualFlushOfCommands();
        DAWN_TRY(SubmitPendingCommands());
        DAWN_ASSERT(serial <= GetLastSubmittedCommandSerial());
    }
    return {};
}

MaybeError ExecutionQueueBase::SubmitPendingCommands() {
    if (mInSubmit) {
        return {};
    }

    mInSubmit = true;
    auto result = SubmitPendingCommandsImpl();
    mInSubmit = false;

    return result;
}

void ExecutionQueueBase::AssumeCommandsComplete() {
    // Bump serials so any pending callbacks can be fired.
    // TODO(crbug.com/dawn/831): This is called during device destroy, which is not
    // thread-safe yet. Two threads calling destroy would race setting these serials.
    ExecutionSerial completed =
        ExecutionSerial(mLastSubmittedSerial.fetch_add(1u, std::memory_order_release) + 1);
    UpdateCompletedSerial(completed);
}

void ExecutionQueueBase::IncrementLastSubmittedCommandSerial() {
    mLastSubmittedSerial.fetch_add(1u, std::memory_order_release);
}

bool ExecutionQueueBase::HasScheduledCommands() const {
    return mLastSubmittedSerial.load(std::memory_order_acquire) >
               mCompletedSerial.load(std::memory_order_acquire) ||
           HasPendingCommands();
}

// All prevously submitted works at the moment will supposedly complete at this serial.
// Internally the serial is computed according to whether frontend and backend have pending
// commands. There are 4 cases of combination:
//   1) Frontend(No), Backend(No)
//   2) Frontend(No), Backend(Yes)
//   3) Frontend(Yes), Backend(No)
//   4) Frontend(Yes), Backend(Yes)
// For case 1, we don't need the serial to track the task as we can ack it right now.
// For case 2 and 4, there will be at least an eventual submission, so we can use
// 'GetPendingCommandSerial' as the serial.
// For case 3, we can't use 'GetPendingCommandSerial' as it won't be submitted surely. Instead we
// use 'GetLastSubmittedCommandSerial', which must be fired eventually.
ExecutionSerial ExecutionQueueBase::GetScheduledWorkDoneSerial() const {
    return HasPendingCommands() ? GetPendingCommandSerial() : GetLastSubmittedCommandSerial();
}

}  // namespace dawn::native