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问使xpdf Pdf2Txt函数成为线程安全
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Stack Overflow用户

提问于 2022-09-19 11:19:55

回答 1查看 111关注 0票数 0

我尝试使用xpdf源代码到MFC应用程序中，将pdf转换成文本。代码示例取自它们的站点(或存储库)：

int Pdf2Txt(std::string PdfFile, std::string TxtFile) const
{
    GString* ownerPW, *userPW;
    UnicodeMap* uMap;
    TextOutputDev* textOut;
    TextOutputControl textOutControl;
    GString* textFileName;

    int exitCode;
    char textEncName[128] = "";
    char textEOL[16] = "";
    GBool noPageBreaks = gFalse;
    GBool quiet = gFalse;
    char ownerPassword[33] = "\001";
    char userPassword[33] = "\001";
    int firstPage = 1;
    int lastPage = 0;
    GBool tableLayout = gFalse;
    double fixedPitch = 0;
    GBool physLayout = gFalse;
    GBool simpleLayout = gFalse;
    GBool simple2Layout = gFalse;
    GBool linePrinter = gFalse;
    GBool rawOrder = gFalse;
    double fixedLineSpacing = 0;
    double marginLeft = 0;
    double marginRight = 0;
    double marginTop = 0;
    double marginBottom = 0;
    GBool clipText = gFalse;
    GBool discardDiag = gFalse;
    GBool insertBOM = gFalse;

    exitCode = 99;

    // read config file
    globalParams = new GlobalParams("");
    if (textEncName[0])
    {
        globalParams->setTextEncoding(textEncName);
    }
    if (textEOL[0])
    {
        if (!globalParams->setTextEOL(textEOL))
        {
            fprintf(stderr, "Bad '-eol' value on command line\n");
        }
    }
    if (noPageBreaks)
    {
        globalParams->setTextPageBreaks(gFalse);
    }
    if (quiet)
    {
        globalParams->setErrQuiet(quiet);
    }

    // Set UNICODE support
    globalParams->setTextEncoding("UTF-8");

    // get mapping to output encoding
    if (!(uMap = globalParams->getTextEncoding()))
    {
        error(errConfig, -1, "Couldn't get text encoding");
        goto err1;
    }

    // open PDF file
    if (ownerPassword[0] != '\001')
    {
        ownerPW = new GString(ownerPassword);
    }
    else
    {
        ownerPW = NULL;
    }
    if (userPassword[0] != '\001')
    {
        userPW = new GString(userPassword);
    }
    else
    {
        userPW = NULL;
    }
    PDFDoc* doc = new PDFDoc((char*)PdfFile.c_str(), ownerPW, userPW);
    if (userPW)
    {
        delete userPW;
    }
    if (ownerPW)
    {
        delete ownerPW;
    }
    if (! doc->isOk())
    {
        exitCode = 1;
        goto err2;
    }

    // check for copy permission
    if (! doc->okToCopy())
    {
        error(errNotAllowed, -1, "Copying of text from this document is not allowed.");
        exitCode = 3;
        goto err2;
    }

    // construct text file name
    textFileName = new GString(TxtFile.c_str());

    // get page range
    if (firstPage < 1)
    {
        firstPage = 1;
    }
    if (lastPage < 1 || lastPage > doc->getNumPages())
    {
        lastPage = doc->getNumPages();
    }

    // write text file
    if (tableLayout)
    {
        textOutControl.mode = textOutTableLayout;
        textOutControl.fixedPitch = fixedPitch;
    }
    else if (physLayout)
    {
        textOutControl.mode = textOutPhysLayout;
        textOutControl.fixedPitch = fixedPitch;
    }
    else if (simpleLayout)
    {
        textOutControl.mode = textOutSimpleLayout;
    }
    else if (simple2Layout)
    {
        textOutControl.mode = textOutSimple2Layout;
    }
    else if (linePrinter)
    {
        textOutControl.mode = textOutLinePrinter;
        textOutControl.fixedPitch = fixedPitch;
        textOutControl.fixedLineSpacing = fixedLineSpacing;
    }
    else if (rawOrder)
    {
        textOutControl.mode = textOutRawOrder;
    }
    else
    {
        textOutControl.mode = textOutReadingOrder;
    }
    textOutControl.clipText = clipText;
    textOutControl.discardDiagonalText = discardDiag;
    textOutControl.insertBOM = insertBOM;
    textOutControl.marginLeft = marginLeft;
    textOutControl.marginRight = marginRight;
    textOutControl.marginTop = marginTop;
    textOutControl.marginBottom = marginBottom;
    textOut = new TextOutputDev(textFileName->getCString(), &textOutControl, gFalse, gTrue);
    if (textOut->isOk())
    {
        doc->displayPages(textOut, firstPage, lastPage, 72, 72, 0, gFalse, gTrue, gFalse);
    }
    else
    {
        delete textOut;
        exitCode = 2;
        goto err3;
    }
    delete textOut;

    exitCode = 0;

    // clean up
err3:
    delete textFileName;
err2:
    delete doc;
//  uMap->decRefCnt();
err1:
    delete globalParams;

    // check for memory leaks
    Object::memCheck(stderr);
    gMemReport(stderr);

    return exitCode;
}

到现在为止还好。但是这段代码并不是线程安全的:如果我尝试在多线程代码中运行这段代码，它会崩溃：

// TextOutputDev.cc
if (uMap->isUnicode())
{

    lreLen = uMap->mapUnicode(0x202a, lre, sizeof(lre)); // <-- crash

为什么？因为有一个变量globalParams，它在函数的最后一行中被删除，并且它对所有线程都很常见：

delete globalParams;

它是GlobalParams.h ( xpdf代码的一部分)中的一个外部全局变量：

// xpdf/GlobalParams.h
// The global parameters object.
extern GlobalParams *globalParams;

如何确保此函数线程安全？因为“问题变量”是在xpdf源代码中，而不是我的.

总之，globalParams是用xpdf代码声明的，并在我的(客户端)代码中进行了清理。

xpdf源代码可以在这里看到：https://github.com/jeroen/xpdf/blob/c2c946f517eb09cfd09d957e0f3b04d44bf6f827/src/poppler/GlobalParams.h

和

https://github.com/jeroen/xpdf/blob/c2c946f517eb09cfd09d957e0f3b04d44bf6f827/src/poppler/GlobalParams.cc

c++

multithreading

mfc

xpdf

回答 1

Stack Overflow用户

回答已采纳

发布于 2022-09-20 10:59:17

尝试重新构造代码，如下所示。我已经将GlobalParams初始化代码移动到一个单独的函数中。在初始化期间，或者在启动调用Pdf2Txt()的线程之前，应该调用此函数(一次)。当然，不应该销毁GlobalParams实例，因为它可以被多个线程使用。它不会损害应用程序的内存，它只是一个对象，而不是很大--嗯，它包含许多int和bool成员变量，但是这些变量占用的空间不多，也占用了相当多的string*变量(我想最初是null或emtpy )，所以最多只有几KB。

bool InitGlobalParams()
{
    UnicodeMap* uMap;
    char textEncName[128] = "";
    char textEOL[16] = "";
    GBool noPageBreaks = gFalse;
    GBool quiet = gFalse;

    // read config file
    globalParams = new GlobalParams(""); // <-- Maybe add some checking code here?
    if (textEncName[0])
    {
        globalParams->setTextEncoding(textEncName);
    }
    if (textEOL[0])
    {
        if (!globalParams->setTextEOL(textEOL))
        {
            fprintf(stderr, "Bad '-eol' value on command line\n");
        }
    }
    if (noPageBreaks)
    {
        globalParams->setTextPageBreaks(gFalse);
    }
    if (quiet)
    {
        globalParams->setErrQuiet(quiet);
    }

    // Set UNICODE support
    globalParams->setTextEncoding("UTF-8");

    // get mapping to output encoding
    if (!(uMap = globalParams->getTextEncoding()))
    {
        error(errConfig, -1, "Couldn't get text encoding");
        return false;
    }
    return true;
}

int Pdf2Txt(std::string PdfFile, std::string TxtFile) const
{
    GString* ownerPW, *userPW;
    TextOutputDev* textOut;
    TextOutputControl textOutControl;
    GString* textFileName;

    int exitCode;
    char ownerPassword[33] = "\001";
    char userPassword[33] = "\001";
    int firstPage = 1;
    int lastPage = 0;
    GBool tableLayout = gFalse;
    double fixedPitch = 0;
    GBool physLayout = gFalse;
    GBool simpleLayout = gFalse;
    GBool simple2Layout = gFalse;
    GBool linePrinter = gFalse;
    GBool rawOrder = gFalse;
    double fixedLineSpacing = 0;
    double marginLeft = 0;
    double marginRight = 0;
    double marginTop = 0;
    double marginBottom = 0;
    GBool clipText = gFalse;
    GBool discardDiag = gFalse;
    GBool insertBOM = gFalse;

    exitCode = 99;

    // open PDF file
    if (ownerPassword[0] != '\001')
    {
        ownerPW = new GString(ownerPassword);
    }
    else
    {
        ownerPW = NULL;
    }
    if (userPassword[0] != '\001')
    {
        userPW = new GString(userPassword);
    }
    else
    {
        userPW = NULL;
    }
    PDFDoc* doc = new PDFDoc((char*)PdfFile.c_str(), ownerPW, userPW);
    if (userPW)
    {
        delete userPW;
    }
    if (ownerPW)
    {
        delete ownerPW;
    }
    if (! doc->isOk())
    {
        exitCode = 1;
        goto err2;
    }

    // check for copy permission
    if (! doc->okToCopy())
    {
        error(errNotAllowed, -1, "Copying of text from this document is not allowed.");
        exitCode = 3;
        goto err2;
    }

    // construct text file name
    textFileName = new GString(TxtFile.c_str());

    // get page range
    if (firstPage < 1)
    {
        firstPage = 1;
    }
    if (lastPage < 1 || lastPage > doc->getNumPages())
    {
        lastPage = doc->getNumPages();
    }

    // write text file
    if (tableLayout)
    {
        textOutControl.mode = textOutTableLayout;
        textOutControl.fixedPitch = fixedPitch;
    }
    else if (physLayout)
    {
        textOutControl.mode = textOutPhysLayout;
        textOutControl.fixedPitch = fixedPitch;
    }
    else if (simpleLayout)
    {
        textOutControl.mode = textOutSimpleLayout;
    }
    else if (simple2Layout)
    {
        textOutControl.mode = textOutSimple2Layout;
    }
    else if (linePrinter)
    {
        textOutControl.mode = textOutLinePrinter;
        textOutControl.fixedPitch = fixedPitch;
        textOutControl.fixedLineSpacing = fixedLineSpacing;
    }
    else if (rawOrder)
    {
        textOutControl.mode = textOutRawOrder;
    }
    else
    {
        textOutControl.mode = textOutReadingOrder;
    }
    textOutControl.clipText = clipText;
    textOutControl.discardDiagonalText = discardDiag;
    textOutControl.insertBOM = insertBOM;
    textOutControl.marginLeft = marginLeft;
    textOutControl.marginRight = marginRight;
    textOutControl.marginTop = marginTop;
    textOutControl.marginBottom = marginBottom;
    textOut = new TextOutputDev(textFileName->getCString(), &textOutControl, gFalse, gTrue);
    if (textOut->isOk())
    {
        doc->displayPages(textOut, firstPage, lastPage, 72, 72, 0, gFalse, gTrue, gFalse);
    }
    else
    {
        delete textOut;
        exitCode = 2;
        goto err3;
    }
    delete textOut;

    exitCode = 0;

    // clean up
err3:
    delete textFileName;
err2:
    delete doc;
//  uMap->decRefCnt();
err1:
    // Do NOT delete the one and only GlobalParams instance!!!
    //delete globalParams;

    // check for memory leaks
    Object::memCheck(stderr);
    gMemReport(stderr);

    return exitCode;
}

上面的代码可能甚至不会编译(我用文本编辑器修改了它，并没有真正测试它)，所以请做可能需要的任何更改。预期xpdf函数不会修改globalParams对象(对于它们来说是“只读”)，因此这段代码有很好的工作机会。顺便说一下，在#if MULTITHREADED类定义(GlobalParams.h)中有一个GlobalParams指令，它的块中包含3个互斥对象。实现代码(GlobalParams.cc)锁定互斥锁以访问GlobalParams成员，因此这可能会导致一些线程稍等片刻，尽管我不知道有多少(必须彻底检查代码，这本身就是一个小“项目”)。你可以试着测试它。

当然，上面@KJ所表达的担忧仍然适用，并行运行许多这样的线程可能会使系统过载(虽然我不确定xpdf是否使用多个线程来处理单个 PDF，请您提供帮助，它是如何配置的？)，尤其是如果您在服务器上运行这个线程不允许太多并发转换--运行转换可能会导致其他进程慢下来。它还可能导致I/O瓶颈(磁盘和/或网络)，因此最初尝试使用少量线程并检查它是如何扩展的。

票数 1

页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持

原文链接：

https://stackoverflow.com/questions/73772580

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