src/dawn/native/ExecutionQueue.cpp

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

#include <atomic>

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.
    uint64_t current = mCompletedSerial.load(std::memory_order_acquire);
    while (uint64_t(completedSerial) > current &&
           !mCompletedSerial.compare_exchange_weak(current, uint64_t(completedSerial),
                                                   std::memory_order_acq_rel)) {
    }
    return {};
}

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

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.
    uint64_t prev = mLastSubmittedSerial.fetch_add(1u, std::memory_order_release);
    mCompletedSerial.store(prev + 1u, std::memory_order_release);
}

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