revert "QProcessEnvironment: simplify locking"

Origin: upstream, https://code.qt.io/cgit/qt/qtbase.git/commit?id=080d61c020678b75
Last-Update: 2026-01-29

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.

Gbp-Pq: Name revert_simplify_locking.diff

diff --git a/src/corelib/io/qprocess.cpp b/src/corelib/io/qprocess.cpp
index 656105dec48ddfa2fab09cdc5732b44366a24b97..fc24ac11a1e32789079cf271cc9913c1e1044446 100644 (file)
--- a/src/corelib/io/qprocess.cpp
+++ b/src/corelib/io/qprocess.cpp
@@ -202,7 +202,6 @@ 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)
@@ -276,6 +275,7 @@ bool QProcessEnvironment::operator==(const QProcessEnvironment &other) const
         return true;
     if (d) {
         if (other.d) {
+            QProcessEnvironmentPrivate::OrderedMutexLocker locker(d, other.d);
             return d->vars == other.d->vars;
         } else {
             return isEmpty();
@@ -322,6 +322,7 @@ bool QProcessEnvironment::contains(const QString &name) const
 {
     if (!d)
         return false;
+    QProcessEnvironmentPrivate::MutexLocker locker(d);
     return d->vars.contains(d->prepareName(name));
 }
 
@@ -372,6 +373,7 @@ 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;
@@ -396,6 +398,7 @@ QStringList QProcessEnvironment::toStringList() const
 {
     if (!d)
         return QStringList();
+    QProcessEnvironmentPrivate::MutexLocker locker(d);
     return d->toList();
 }
 
@@ -409,6 +412,7 @@ QStringList QProcessEnvironment::keys() const
 {
     if (!d)
         return QStringList();
+    QProcessEnvironmentPrivate::MutexLocker locker(d);
     return d->keys();
 }
 
@@ -425,6 +429,7 @@ 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 2587530c09586a4bd8309790e536fb31726677e0..d02e87837c4b2d58b1e97a580a94795fb5eb4ceb 100644 (file)
--- a/src/corelib/io/qprocess_p.h
+++ b/src/corelib/io/qprocess_p.h
@@ -146,22 +146,16 @@ 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
-    {
-        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();
@@ -170,27 +164,40 @@ 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
+    {
+        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
@@ -201,7 +208,8 @@ 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 0435180fa8721c9a22b6aa5d82fe5d5d0cd33a5f..e8f40c90e701e67e6f2e0601eaa7ca5643673ec2 100644 (file)
--- a/src/corelib/io/qprocess_unix.cpp
+++ b/src/corelib/io/qprocess_unix.cpp
@@ -439,6 +439,7 @@ void QProcessPrivate::startProcess()
     int envc = 0;
     char **envp = nullptr;
     if (environment.d.constData()) {
+        QProcessEnvironmentPrivate::MutexLocker locker(environment.d);
         envp = _q_dupEnvironment(environment.d.constData()->vars, &envc);
     }
 
@@ -980,6 +981,7 @@ bool QProcessPrivate::startDetached(qint64 *pid)
             int envc = 0;
             char **envp = nullptr;
             if (environment.d.constData()) {
+                QProcessEnvironmentPrivate::MutexLocker locker(environment.d);
                 envp = _q_dupEnvironment(environment.d.constData()->vars, &envc);
             }