[PATCH] Revert "QProcessEnvironment: simplify locking"

This reverts commit c5d6b263c204cb09db2be36826e19acb03dc24fb.

The commit being reverted assumes the mutex is only protecting 'nameMap'
and nothing else is mutable, which is false. The mutex is not only
protecting 'nameMap' but also protecting the containing value objects,
since even though the value object is accessed read-only, its
implementation mutates its internal states for 2-way conversion between
ByteArray and QString.

Commit 85e61297f7b02297641826332dbdbc845a88c34b ("restore
QProcessEnvironment shared data thread safety on unix") said that
implicit sharing together with 'mutable' is a time bomb and the bomb is
triggered by the reverted commit.

Fixes: QTBUG-142938
Pick-to: 6.11 6.10 6.8
Change-Id: I9e3234f0eb2c691eccf753a11f63fae9944bd503
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Gbp-Pq: Name upstream_revert_simplify_locking.diff

diff --git a/src/corelib/io/qprocess.cpp b/src/corelib/io/qprocess.cpp
index e03fc3dfe852a98ee1f1644b827b002d71fdb7ce..4a30bb7c967b47b6a0636747a1d485091701dcfd 100644 (file)
--- a/src/corelib/io/qprocess.cpp
+++ b/src/corelib/io/qprocess.cpp
@@ -105,7 +105,6 @@ void QProcessEnvironmentPrivate::insert(const QProcessEnvironmentPrivate &other)
         vars.insert(it.key(), it.value());
 
 #ifdef Q_OS_UNIX
-    const OrderedNameMapMutexLocker locker(this, &other);
     auto nit = other.nameMap.constBegin();
     const auto nend = other.nameMap.constEnd();
     for ( ; nit != nend; ++nit)
@@ -206,8 +205,10 @@ bool comparesEqual(const QProcessEnvironment &lhs, const QProcessEnvironment &rh
 {
     if (lhs.d == rhs.d)
         return true;
-
-    return lhs.d && rhs.d && lhs.d->vars == rhs.d->vars;
+    if (!(lhs.d && rhs.d))
+        return false;
+    QProcessEnvironmentPrivate::OrderedMutexLocker locker(lhs.d, rhs.d);
+    return lhs.d->vars == rhs.d->vars;
 }
 
 /*!
@@ -265,6 +266,7 @@ bool QProcessEnvironment::contains(const QString &name) const
 {
     if (!d)
         return false;
+    QProcessEnvironmentPrivate::MutexLocker locker(d);
     return d->vars.contains(d->prepareName(name));
 }
 
@@ -315,6 +317,7 @@ QString QProcessEnvironment::value(const QString &name, const QString &defaultVa
     if (!d)
         return defaultValue;
 
+    QProcessEnvironmentPrivate::MutexLocker locker(d);
     const auto it = d->vars.constFind(d->prepareName(name));
     if (it == d->vars.constEnd())
         return defaultValue;
@@ -339,6 +342,7 @@ QStringList QProcessEnvironment::toStringList() const
 {
     if (!d)
         return QStringList();
+    QProcessEnvironmentPrivate::MutexLocker locker(d);
     return d->toList();
 }
 
@@ -355,6 +359,7 @@ QStringList QProcessEnvironment::keys() const
 {
     if (!d)
         return QStringList();
+    QProcessEnvironmentPrivate::MutexLocker locker(d);
     return d->keys();
 }
 
@@ -371,6 +376,7 @@ void QProcessEnvironment::insert(const QProcessEnvironment &e)
         return;
 
     // our re-impl of detach() detaches from null
+    QProcessEnvironmentPrivate::MutexLocker locker(e.d);
     d->insert(*e.d);
 }
 

diff --git a/src/corelib/io/qprocess_p.h b/src/corelib/io/qprocess_p.h
index 9510101e7454e1504c2eede1add7835803f843da..cb86968b7529ee8c7b3bfd320f7b2f313ae315a4 100644 (file)
--- a/src/corelib/io/qprocess_p.h
+++ b/src/corelib/io/qprocess_p.h
@@ -110,22 +110,16 @@ public:
     inline QString nameToString(const Key &name) const { return name; }
     inline Value prepareValue(const QString &value) const { return value; }
     inline QString valueToString(const Value &value) const { return value; }
-#else
-    struct NameMapMutexLocker : public QMutexLocker<QMutex>
-    {
-        NameMapMutexLocker(const QProcessEnvironmentPrivate *d) : QMutexLocker(&d->nameMapMutex) {}
+    struct MutexLocker {
+        MutexLocker(const QProcessEnvironmentPrivate *) {}
     };
-    struct OrderedNameMapMutexLocker : public QOrderedMutexLocker
-    {
-        OrderedNameMapMutexLocker(const QProcessEnvironmentPrivate *d1,
-                                  const QProcessEnvironmentPrivate *d2)
-            : QOrderedMutexLocker(&d1->nameMapMutex, &d2->nameMapMutex)
-        {}
+    struct OrderedMutexLocker {
+        OrderedMutexLocker(const QProcessEnvironmentPrivate *,
+                           const QProcessEnvironmentPrivate *) {}
     };
-
+#else
     inline Key prepareName(const QString &name) const
     {
-        const NameMapMutexLocker locker(this);
         Key &ent = nameMap[name];
         if (ent.isEmpty())
             ent = name.toLocal8Bit();
@@ -134,27 +128,40 @@ public:
     inline QString nameToString(const Key &name) const
     {
         const QString sname = QString::fromLocal8Bit(name);
-        {
-            const NameMapMutexLocker locker(this);
-            nameMap[sname] = name;
-        }
+        nameMap[sname] = name;
         return sname;
     }
     inline Value prepareValue(const QString &value) const { return Value(value); }
     inline QString valueToString(const Value &value) const { return value.string(); }
 
+    struct MutexLocker : public QMutexLocker<QMutex>
+    {
+        MutexLocker(const QProcessEnvironmentPrivate *d) : QMutexLocker(&d->mutex) {}
+    };
+    struct OrderedMutexLocker : public QOrderedMutexLocker
+    {
+        OrderedMutexLocker(const QProcessEnvironmentPrivate *d1,
+                           const QProcessEnvironmentPrivate *d2) :
+            QOrderedMutexLocker(&d1->mutex, &d2->mutex)
+        {}
+    };
+
     QProcessEnvironmentPrivate() : QSharedData() {}
     QProcessEnvironmentPrivate(const QProcessEnvironmentPrivate &other) :
-        QSharedData(), vars(other.vars)
+        QSharedData()
     {
+        // This being locked ensures that the functions that only assign
+        // d pointers don't need explicit locking.
         // We don't need to lock our own mutex, as this object is new and
         // consequently not shared. For the same reason, non-const methods
         // do not need a lock, as they detach objects (however, we need to
         // ensure that they really detach before using prepareName()).
-        NameMapMutexLocker locker(&other);
+        MutexLocker locker(&other);
+        vars = other.vars;
         nameMap = other.nameMap;
-        // We need to detach our nameMap, so that our mutex can protect it.
-        // As we are being detached, it likely would be detached a moment later anyway.
+        // We need to detach our members, so that our mutex can protect them.
+        // As we are being detached, they likely would be detached a moment later anyway.
+        vars.detach();
         nameMap.detach();
     }
 #endif
@@ -165,7 +172,8 @@ public:
 #ifdef Q_OS_UNIX
     typedef QHash<QString, Key> NameHash;
     mutable NameHash nameMap;
-    mutable QMutex nameMapMutex;
+
+    mutable QMutex mutex;
 #endif
 
     static QProcessEnvironment fromList(const QStringList &list);

diff --git a/src/corelib/io/qprocess_unix.cpp b/src/corelib/io/qprocess_unix.cpp
index d9b672df11d7b48e6fc61cad6600305406bf0b95..e269bddadfd9335793d6b20ad65f063f234f8110 100644 (file)
--- a/src/corelib/io/qprocess_unix.cpp
+++ b/src/corelib/io/qprocess_unix.cpp
@@ -398,6 +398,8 @@ QChildProcess::CharPointerList::CharPointerList(const QProcessEnvironmentPrivate
     if (!environment)
         return;
 
+    QProcessEnvironmentPrivate::MutexLocker locker(environment);
+
     const QProcessEnvironmentPrivate::Map &env = environment->vars;
     qsizetype count = env.size();
     pointers.reset(new char *[count + 1]);