qsharedpointer.cpp

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// Copyright (C) 2020 The Qt Company Ltd.
// Copyright (C) 2020 Intel Corporation.
// Copyright (C) 2019 Klarälvdalens Datakonsult AB.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
 
#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
 
QT6_ONLY(
void QtSharedPointer::ExternalRefCountData::setQObjectShared(const QObject *, bool)
{}
)
 
QT6_ONLY(
void QtSharedPointer::ExternalRefCountData::checkQObjectShared(const QObject *)
{
    if (strongref.loadRelaxed() < 0)
        qWarning("QSharedPointer: cannot create a QSharedPointer from a QObject-tracking QWeakPointer");
}
)
 
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.loadRelaxed();
    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.storeRelaxed(-1);
    x->weakref.storeRelaxed(2);  // the QWeakPointer that called us plus the QObject itself
 
    ExternalRefCountData *ret;
    if (d->sharedRefcount.testAndSetOrdered(nullptr, x, ret)) {     // ought to be release+acquire; this is acq_rel+acquire
        ret = x;
    } else {
        // ~ExternalRefCountData has a Q_ASSERT, so we use this trick to
        // only execute this if Q_ASSERTs are enabled
        Q_ASSERT((x->weakref.storeRelaxed(0), true));
        ::delete x;
        ret->weakref.ref();
    }
    return ret;
}
 
QSharedPointer<QObject> QtSharedPointer::sharedPointerFromVariant_internal(const QVariant &variant)
{
    Q_ASSERT(variant.metaType().flags() & QMetaType::SharedPointerToQObject);
    return *reinterpret_cast<const QSharedPointer<QObject>*>(variant.constData());
}
 
QWeakPointer<QObject> QtSharedPointer::weakPointerFromVariant_internal(const QVariant &variant)
{
    Q_ASSERT(variant.metaType().flags() & QMetaType::WeakPointerToQObject ||
             variant.metaType().flags() & QMetaType::TrackingPointerToQObject);
    return *reinterpret_cast<const QWeakPointer<QObject>*>(variant.constData());
}
 
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_DARWIN)
#      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_AUTOTEST_EXPORT void internalSafetyCheckCleanCheck();
}
 
void QtSharedPointer::internalSafetyCheckAdd(const void *d_ptr, const volatile void *ptr)
{
    KnownPointers *const kp = knownPointers();
    if (!kp)
        return;                 // end-game: the application is being destroyed already
 
    if (!ptr) {
        // nullptr is allowed to be tracked by more than one QSharedPointer, so we
        // need something else to put in our tracking structures
        ptr = d_ptr;
    }
 
    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, nullptr);
    if (Q_UNLIKELY(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::internalSafetyCheckRemove(const void *d_ptr)
{
    KnownPointers *const kp = knownPointers();
    if (!kp)
        return;                 // end-game: the application is being destroyed already
 
    QMutexLocker lock(&kp->mutex);
 
    const auto it = kp->dPointers.constFind(d_ptr);
    if (Q_UNLIKELY(it == kp->dPointers.cend())) {
        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);
    }
 
    const auto it2 = kp->dataPointers.constFind(it->pointer);
    Q_ASSERT(it2 != kp->dataPointers.cend());
 
    //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 (Q_UNLIKELY(kp->dPointers.size() != kp->dataPointers.size()))
        qFatal("Internal consistency error: the number of pointers is not equal!");
 
    if (Q_UNLIKELY(!kp->dPointers.isEmpty()))
        qFatal("Pointer cleaning failed: %d entries remaining", int(kp->dPointers.size()));
#  endif
}
 
QT_END_NAMESPACE