qsharedpointer.cpp

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#include "qsharedpointer.h"

// to be sure we aren't causing a namespace clash:
#include "qshareddata.h"

#include <qset.h>
#include <qmutex.h>

#if !defined(QT_NO_QOBJECT)
#include "private/qobject_p.h"

QT_BEGIN_NAMESPACE

void QtSharedPointer::ExternalRefCountData::setQObjectShared(const QObject *obj, bool)
{
    Q_ASSERT(obj);
    QObjectPrivate *d = QObjectPrivate::get(const_cast<QObject *>(obj));

    if (d->sharedRefcount)
        qFatal("QSharedPointer: pointer %p already has reference counting", obj);
    d->sharedRefcount = this;

    // QObject decreases the refcount too, so increase it up
    weakref.ref();
}

QtSharedPointer::ExternalRefCountData *QtSharedPointer::ExternalRefCountData::getAndRef(const QObject *obj)
{
    Q_ASSERT(obj);
    QObjectPrivate *d = QObjectPrivate::get(const_cast<QObject *>(obj));
    Q_ASSERT_X(!d->wasDeleted, "QWeakPointer", "Detected QWeakPointer creation in a QObject being deleted");

    ExternalRefCountData *that = d->sharedRefcount;
    if (that) {
        that->weakref.ref();
        return that;
    }

    // we can create the refcount data because it doesn't exist
    ExternalRefCountData *x = new ExternalRefCountData(Qt::Uninitialized);
    x->strongref = -1;
    x->weakref = 2;  // the QWeakPointer that called us plus the QObject itself
    if (!d->sharedRefcount.testAndSetRelease(0, x)) {
        delete x;
        d->sharedRefcount->weakref.ref();
    }
    return d->sharedRefcount;
}

QT_END_NAMESPACE

#endif



//#  define QT_SHARED_POINTER_BACKTRACE_SUPPORT
#  ifdef QT_SHARED_POINTER_BACKTRACE_SUPPORT
#    if defined(__GLIBC__) && (__GLIBC__ >= 2) && !defined(__UCLIBC__) && !defined(QT_LINUXBASE)
#      define BACKTRACE_SUPPORTED
#    elif defined(Q_OS_MACX)
#      define BACKTRACE_SUPPORTED
#    endif
#  endif

#  if defined(BACKTRACE_SUPPORTED)
#    include <sys/types.h>
#    include <execinfo.h>
#    include <stdio.h>
#    include <unistd.h>
#    include <sys/wait.h>

QT_BEGIN_NAMESPACE

static inline QByteArray saveBacktrace() __attribute__((always_inline));
static inline QByteArray saveBacktrace()
{
    static const int maxFrames = 32;

    QByteArray stacktrace;
    stacktrace.resize(sizeof(void*) * maxFrames);
    int stack_size = backtrace((void**)stacktrace.data(), maxFrames);
    stacktrace.resize(sizeof(void*) * stack_size);

    return stacktrace;
}

static void printBacktrace(QByteArray stacktrace)
{
    void *const *stack = (void *const *)stacktrace.constData();
    int stack_size = stacktrace.size() / sizeof(void*);
    char **stack_symbols = backtrace_symbols(stack, stack_size);

    int filter[2];
    pid_t child = -1;
    if (pipe(filter) != -1)
        child = fork();
    if (child == 0) {
        // child process
        dup2(fileno(stderr), fileno(stdout));
        dup2(filter[0], fileno(stdin));
        close(filter[0]);
        close(filter[1]);
        execlp("c++filt", "c++filt", "-n", NULL);

        // execlp failed
        execl("/bin/cat", "/bin/cat", NULL);
        _exit(127);
    }

    // parent process
    close(filter[0]);
    FILE *output;
    if (child == -1) {
        // failed forking
        close(filter[1]);
        output = stderr;
    } else {
        output = fdopen(filter[1], "w");
    }

    fprintf(stderr, "Backtrace of the first creation (most recent frame first):\n");
    for (int i = 0; i < stack_size; ++i) {
        if (strlen(stack_symbols[i]))
            fprintf(output, "#%-2d %s\n", i, stack_symbols[i]);
        else
            fprintf(output, "#%-2d %p\n", i, stack[i]);
    }

    if (child != -1) {
        fclose(output);
        waitpid(child, 0, 0);
    }
}

QT_END_NAMESPACE

#  endif  // BACKTRACE_SUPPORTED

namespace {
    QT_USE_NAMESPACE
    struct Data {
        const volatile void *pointer;
#  ifdef BACKTRACE_SUPPORTED
        QByteArray backtrace;
#  endif
    };

    class KnownPointers
    {
    public:
        QMutex mutex;
        QHash<const void *, Data> dPointers;
        QHash<const volatile void *, const void *> dataPointers;
    };
}

Q_GLOBAL_STATIC(KnownPointers, knownPointers)

QT_BEGIN_NAMESPACE

namespace QtSharedPointer {
    Q_CORE_EXPORT void internalSafetyCheckAdd(const volatile void *);
    Q_CORE_EXPORT void internalSafetyCheckRemove(const volatile void *);
    Q_AUTOTEST_EXPORT void internalSafetyCheckCleanCheck();
}

void QtSharedPointer::internalSafetyCheckAdd(const volatile void *)
{
    // Qt 4.5 compatibility
    // this function is broken by design, so it was replaced with internalSafetyCheckAdd2
    //
    // it's broken because we tracked the pointers added and
    // removed from QSharedPointer, converted to void*.
    // That is, this is supposed to track the "top-of-object" pointer in
    // case of multiple inheritance.
    //
    // However, it doesn't work well in some compilers:
    // if you create an object with a class of type A and the last reference
    // is dropped of type B, then the value passed to internalSafetyCheckRemove could
    // be different than was added. That would leave dangling addresses.
    //
    // So instead, we track the pointer by the d-pointer instead.
}

void QtSharedPointer::internalSafetyCheckRemove(const volatile void *)
{
    // Qt 4.5 compatibility
    // see comments above
}

void QtSharedPointer::internalSafetyCheckAdd2(const void *d_ptr, const volatile void *ptr)
{
    // see comments above for the rationale for this function
    KnownPointers *const kp = knownPointers();
    if (!kp)
        return;                 // end-game: the application is being destroyed already

    QMutexLocker lock(&kp->mutex);
    Q_ASSERT(!kp->dPointers.contains(d_ptr));

    //qDebug("Adding d=%p value=%p", d_ptr, ptr);

    const void *other_d_ptr = kp->dataPointers.value(ptr, 0);
    if (other_d_ptr) {
#  ifdef BACKTRACE_SUPPORTED
        printBacktrace(knownPointers()->dPointers.value(other_d_ptr).backtrace);
#  endif
        qFatal("QSharedPointer: internal self-check failed: pointer %p was already tracked "
               "by another QSharedPointer object %p", ptr, other_d_ptr);
    }

    Data data;
    data.pointer = ptr;
#  ifdef BACKTRACE_SUPPORTED
    data.backtrace = saveBacktrace();
#  endif

    kp->dPointers.insert(d_ptr, data);
    kp->dataPointers.insert(ptr, d_ptr);
    Q_ASSERT(kp->dPointers.size() == kp->dataPointers.size());
}

void QtSharedPointer::internalSafetyCheckRemove2(const void *d_ptr)
{
    KnownPointers *const kp = knownPointers();
    if (!kp)
        return;                 // end-game: the application is being destroyed already

    QMutexLocker lock(&kp->mutex);

    QHash<const void *, Data>::iterator it = kp->dPointers.find(d_ptr);
    if (it == kp->dPointers.end()) {
        qFatal("QSharedPointer: internal self-check inconsistency: pointer %p was not tracked. "
               "To use QT_SHAREDPOINTER_TRACK_POINTERS, you have to enable it throughout "
               "in your code.", d_ptr);
    }

    QHash<const volatile void *, const void *>::iterator it2 = kp->dataPointers.find(it->pointer);
    Q_ASSERT(it2 != kp->dataPointers.end());

    //qDebug("Removing d=%p value=%p", d_ptr, it->pointer);

    // remove entries
    kp->dataPointers.erase(it2);
    kp->dPointers.erase(it);
    Q_ASSERT(kp->dPointers.size() == kp->dataPointers.size());
}

void QtSharedPointer::internalSafetyCheckCleanCheck()
{
#  ifdef QT_BUILD_INTERNAL
    KnownPointers *const kp = knownPointers();
    Q_ASSERT_X(kp, "internalSafetyCheckSelfCheck()", "Called after global statics deletion!");

    if (kp->dPointers.size() != kp->dataPointers.size())
        qFatal("Internal consistency error: the number of pointers is not equal!");

    if (!kp->dPointers.isEmpty())
        qFatal("Pointer cleaning failed: %d entries remaining", kp->dPointers.size());
#  endif
}

QT_END_NAMESPACE