melonDS/src/NDSCart_SRAMManager.cpp

/*
    Copyright 2016-2021 Arisotura

    This file is part of melonDS.

    melonDS is free software: you can redistribute it and/or modify it under
    the terms of the GNU General Public License as published by the Free
    Software Foundation, either version 3 of the License, or (at your option)
    any later version.

    melonDS is distributed in the hope that it will be useful, but WITHOUT ANY
    WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
    FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

    You should have received a copy of the GNU General Public License along
    with melonDS. If not, see http://www.gnu.org/licenses/.
*/

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <time.h>
#include <atomic>
#include "NDSCart_SRAMManager.h"
#include "Platform.h"

namespace NDSCart_SRAMManager
{

Platform::Thread* FlushThread;
std::atomic_bool FlushThreadRunning;
Platform::Mutex* SecondaryBufferLock;

char Path[1024];

u8* Buffer;
u32 Length;

u8* SecondaryBuffer;
u32 SecondaryBufferLength;

time_t TimeAtLastFlushRequest;

// We keep versions in case the user closes the application before
// a flush cycle is finished.
u32 PreviousFlushVersion;
u32 FlushVersion;

void FlushThreadFunc();

bool Init()
{
    SecondaryBufferLock = Platform::Mutex_Create();

    return true;
}

void DeInit()
{
    if (FlushThreadRunning)
    {
        FlushThreadRunning = false;
        Platform::Thread_Wait(FlushThread);
        Platform::Thread_Free(FlushThread);
        FlushSecondaryBuffer();
    }

    if (SecondaryBuffer) delete[] SecondaryBuffer;
    SecondaryBuffer = NULL;

    Platform::Mutex_Free(SecondaryBufferLock);
}

void Setup(const char* path, u8* buffer, u32 length)
{
    // Flush SRAM in case there is unflushed data from previous state.
    FlushSecondaryBuffer();

    Platform::Mutex_Lock(SecondaryBufferLock);

    strncpy(Path, path, 1023);
    Path[1023] = '\0';

    Buffer = buffer;
    Length = length;

    if(SecondaryBuffer) delete[] SecondaryBuffer; // Delete secondary buffer, there might be previous state.

    SecondaryBuffer = new u8[length];
    SecondaryBufferLength = length;

    FlushVersion = 0;
    PreviousFlushVersion = 0;
    TimeAtLastFlushRequest = 0;

    Platform::Mutex_Unlock(SecondaryBufferLock);

    if (path[0] != '\0' && !FlushThreadRunning)
    {
        FlushThread = Platform::Thread_Create(FlushThreadFunc);
        FlushThreadRunning = true;
    }
    else if (path[0] == '\0' && FlushThreadRunning)
    {
        FlushThreadRunning = false;
        Platform::Thread_Wait(FlushThread);
        Platform::Thread_Free(FlushThread);
    }
}

void RequestFlush()
{
    Platform::Mutex_Lock(SecondaryBufferLock);
    printf("NDS SRAM: Flush requested\n");
    memcpy(SecondaryBuffer, Buffer, Length);
    FlushVersion++;
    TimeAtLastFlushRequest = time(NULL);
    Platform::Mutex_Unlock(SecondaryBufferLock);
}

void FlushThreadFunc()
{
    for (;;)
    {
        Platform::Sleep(100 * 1000); // 100ms

        if (!FlushThreadRunning) return;
        
        // We debounce for two seconds after last flush request to ensure that writing has finished.
        if (TimeAtLastFlushRequest == 0 || difftime(time(NULL), TimeAtLastFlushRequest) < 2)
        {
            continue;
        }

        FlushSecondaryBuffer();
    }
}

void FlushSecondaryBuffer(u8* dst, s32 dstLength)
{
    // When flushing to a file, there's no point in re-writing the exact same data.
    if (!dst && !NeedsFlush()) return;
    // When flushing to memory, we don't know if dst already has any data so we only check that we CAN flush.
    if (dst && dstLength < SecondaryBufferLength) return;

    Platform::Mutex_Lock(SecondaryBufferLock);
    if (dst)
    {
        memcpy(dst, SecondaryBuffer, SecondaryBufferLength);
    }
    else
    {
        FILE* f = Platform::OpenFile(Path, "wb");
        if (f)
        {
            printf("NDS SRAM: Written\n");
            fwrite(SecondaryBuffer, SecondaryBufferLength, 1, f);
            fclose(f);
        }
    }
    PreviousFlushVersion = FlushVersion;
    TimeAtLastFlushRequest = 0;
    Platform::Mutex_Unlock(SecondaryBufferLock);
}

bool NeedsFlush()
{
    return FlushVersion != PreviousFlushVersion;
}

void UpdateBuffer(u8* src, s32 srcLength)
{
    if (!src || srcLength != Length) return;

    // should we create a lock for the primary buffer? this method is not intended to be called from a secondary thread in the way Flush is
    memcpy(Buffer, src, srcLength);
    Platform::Mutex_Lock(SecondaryBufferLock);
    memcpy(SecondaryBuffer, src, srcLength);
    Platform::Mutex_Unlock(SecondaryBufferLock);

    PreviousFlushVersion = FlushVersion;
}

}