citra/src/core/hle/kernel/server_session.cpp

// Copyright 2016 Citra Emulator Project
// Licensed under GPLv2 or any later version
// Refer to the license.txt file included.

#include <tuple>

#include "core/hle/kernel/client_port.h"
#include "core/hle/kernel/client_session.h"
#include "core/hle/kernel/hle_ipc.h"
#include "core/hle/kernel/server_session.h"
#include "core/hle/kernel/session.h"
#include "core/hle/kernel/thread.h"

namespace Kernel {

ServerSession::ServerSession(KernelSystem& kernel) : WaitObject(kernel) {}
ServerSession::~ServerSession() {
    // This destructor will be called automatically when the last ServerSession handle is closed by
    // the emulated application.

    // Decrease the port's connection count.
    if (parent->port)
        parent->port->ConnectionClosed();

    // TODO(Subv): Wake up all the ClientSession's waiting threads and set
    // the SendSyncRequest result to 0xC920181A.

    parent->server = nullptr;
}

ResultVal<SharedPtr<ServerSession>> ServerSession::Create(KernelSystem& kernel, std::string name) {
    SharedPtr<ServerSession> server_session(new ServerSession(kernel));

    server_session->name = std::move(name);
    server_session->parent = nullptr;

    return MakeResult(std::move(server_session));
}

bool ServerSession::ShouldWait(Thread* thread) const {
    // Closed sessions should never wait, an error will be returned from svcReplyAndReceive.
    if (parent->client == nullptr)
        return false;
    // Wait if we have no pending requests, or if we're currently handling a request.
    return pending_requesting_threads.empty() || currently_handling != nullptr;
}

void ServerSession::Acquire(Thread* thread) {
    ASSERT_MSG(!ShouldWait(thread), "object unavailable!");

    // If the client endpoint was closed, don't do anything. This ServerSession is now useless and
    // will linger until its last handle is closed by the running application.
    if (parent->client == nullptr)
        return;

    // We are now handling a request, pop it from the stack.
    ASSERT(!pending_requesting_threads.empty());
    currently_handling = pending_requesting_threads.back();
    pending_requesting_threads.pop_back();
}

ResultCode ServerSession::HandleSyncRequest(SharedPtr<Thread> thread) {
    // The ServerSession received a sync request, this means that there's new data available
    // from its ClientSession, so wake up any threads that may be waiting on a svcReplyAndReceive or
    // similar.

    // If this ServerSession has an associated HLE handler, forward the request to it.
    if (hle_handler != nullptr) {
        hle_handler->HandleSyncRequest(SharedPtr<ServerSession>(this));
    }

    if (thread->status == ThreadStatus::Running) {
        // Put the thread to sleep until the server replies, it will be awoken in
        // svcReplyAndReceive for LLE servers.
        thread->status = ThreadStatus::WaitIPC;

        if (hle_handler != nullptr) {
            // For HLE services, we put the request threads to sleep for a short duration to
            // simulate IPC overhead, but only if the HLE handler didn't put the thread to sleep for
            // other reasons like an async callback. The IPC overhead is needed to prevent
            // starvation when a thread only does sync requests to HLE services while a
            // lower-priority thread is waiting to run.

            // This delay was approximated in a homebrew application by measuring the average time
            // it takes for svcSendSyncRequest to return when performing the SetLcdForceBlack IPC
            // request to the GSP:GPU service in a n3DS with firmware 11.6. The measured values have
            // a high variance and vary between models.
            static constexpr u64 IPCDelayNanoseconds = 39000;
            thread->WakeAfterDelay(IPCDelayNanoseconds);
        } else {
            // Add the thread to the list of threads that have issued a sync request with this
            // server.
            pending_requesting_threads.push_back(std::move(thread));
        }
    }

    // If this ServerSession does not have an HLE implementation, just wake up the threads waiting
    // on it.
    WakeupAllWaitingThreads();
    return RESULT_SUCCESS;
}

std::tuple<SharedPtr<ServerSession>, SharedPtr<ClientSession>> KernelSystem::CreateSessionPair(
    const std::string& name, SharedPtr<ClientPort> port) {
    auto server_session = ServerSession::Create(*this, name + "_Server").Unwrap();
    SharedPtr<ClientSession> client_session(new ClientSession(*this));
    client_session->name = name + "_Client";

    std::shared_ptr<Session> parent(new Session);
    parent->client = client_session.get();
    parent->server = server_session.get();
    parent->port = port;

    client_session->parent = parent;
    server_session->parent = parent;

    return std::make_tuple(std::move(server_session), std::move(client_session));
}

} // namespace Kernel