mutex.cpp

// Copyright 2014 Citra Emulator Project
// Licensed under GPLv2 or any later version
// Refer to the license.txt file included.

#include <map>
#include <vector>

#include "common/common.h"

#include "core/hle/kernel/kernel.h"
#include "core/hle/kernel/mutex.h"
#include "core/hle/kernel/thread.h"

namespace Kernel {

class Mutex : public WaitObject {
public:
    std::string GetTypeName() const override { return "Mutex"; }
    std::string GetName() const override { return name; }

    static const HandleType HANDLE_TYPE = HandleType::Mutex;
    HandleType GetHandleType() const override { return HANDLE_TYPE; }

    bool initial_locked;                        ///< Initial lock state when mutex was created
    bool locked;                                ///< Current locked state
    std::string name;                           ///< Name of mutex (optional)
    SharedPtr<Thread> holding_thread;           ///< Thread that has acquired the mutex

    bool ShouldWait() override;
    void Acquire() override;
};

////////////////////////////////////////////////////////////////////////////////////////////////////

typedef std::multimap<SharedPtr<Thread>, SharedPtr<Mutex>> MutexMap;
static MutexMap g_mutex_held_locks;

/**
 * Acquires the specified mutex for the specified thread
 * @param mutex Mutex that is to be acquired
 * @param thread Thread that will acquire the mutex
 */
void MutexAcquireLock(Mutex* mutex, Thread* thread) {
    g_mutex_held_locks.insert(std::make_pair(thread, mutex));
    mutex->holding_thread = thread;
}

/**
 * Resumes a thread waiting for the specified mutex
 * @param mutex The mutex that some thread is waiting on
 */
void ResumeWaitingThread(Mutex* mutex) {
    // Find the next waiting thread for the mutex...
    auto next_thread = mutex->WakeupNextThread();
    if (next_thread != nullptr) {
        MutexAcquireLock(mutex, next_thread);
    } else {
        // Reset mutex lock thread handle, nothing is waiting
        mutex->locked = false;
        mutex->holding_thread = nullptr;
    }
}

void ReleaseThreadMutexes(Thread* thread) {
    auto locked = g_mutex_held_locks.equal_range(thread);
    
    // Release every mutex that the thread holds, and resume execution on the waiting threads
    for (auto iter = locked.first; iter != locked.second; ++iter) {
        ResumeWaitingThread(iter->second.get());
    }

    // Erase all the locks that this thread holds
    g_mutex_held_locks.erase(thread);
}

bool ReleaseMutex(Mutex* mutex) {
    if (mutex->locked) {
        auto locked = g_mutex_held_locks.equal_range(mutex->holding_thread);

        for (MutexMap::iterator iter = locked.first; iter != locked.second; ++iter) {
            if (iter->second == mutex) {
                g_mutex_held_locks.erase(iter);
                break;
            }
        }

        ResumeWaitingThread(mutex);
    }
    return true;
}

/**
 * Releases a mutex
 * @param handle Handle to mutex to release
 */
ResultCode ReleaseMutex(Handle handle) {
    Mutex* mutex = Kernel::g_handle_table.Get<Mutex>(handle).get();
    if (mutex == nullptr) return InvalidHandle(ErrorModule::Kernel);

    if (!ReleaseMutex(mutex)) {
        // TODO(yuriks): Verify error code, this one was pulled out of thin air. I'm not even sure
        // what error condition this is supposed to be signaling.
        return ResultCode(ErrorDescription::AlreadyDone, ErrorModule::Kernel,
                ErrorSummary::NothingHappened, ErrorLevel::Temporary);
    }
    return RESULT_SUCCESS;
}

/**
 * Creates a mutex
 * @param handle Reference to handle for the newly created mutex
 * @param initial_locked Specifies if the mutex should be locked initially
 * @param name Optional name of mutex
 * @return Pointer to new Mutex object
 */
Mutex* CreateMutex(Handle& handle, bool initial_locked, const std::string& name) {
    Mutex* mutex = new Mutex;
    // TODO(yuriks): Fix error reporting
    handle = Kernel::g_handle_table.Create(mutex).ValueOr(INVALID_HANDLE);

    mutex->locked = mutex->initial_locked = initial_locked;
    mutex->name = name;
    mutex->holding_thread = nullptr;

    // Acquire mutex with current thread if initialized as locked...
    if (mutex->locked)
        MutexAcquireLock(mutex, GetCurrentThread());

    return mutex;
}

/**
 * Creates a mutex
 * @param initial_locked Specifies if the mutex should be locked initially
 * @param name Optional name of mutex
 * @return Handle to newly created object
 */
Handle CreateMutex(bool initial_locked, const std::string& name) {
    Handle handle;
    Mutex* mutex = CreateMutex(handle, initial_locked, name);
    return handle;
}

bool Mutex::ShouldWait() {
    return locked && holding_thread != GetCurrentThread();
}

void Mutex::Acquire() {
    _assert_msg_(Kernel, !ShouldWait(), "object unavailable!");
    locked = true;
    MutexAcquireLock(this, GetCurrentThread());
}

} // namespace