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JNI: remove the environment check in QJniObject again

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This amends 944200b5a9705a7617f82cdaf5caf8932380aba4 and the follow-up
commit 84e70976f3d3df8ac921877d32c1dd884fd64267. We have too many use
cases in Qt where we construct a QJniObject from one thread, and access
it from others. Remove the overhead of checking and warning about the
mismatches.

The responsibility of guarding access to the underlying Java object, by
using MonitorEnter/Exit or synchronization blocks in Java, is with the
caller.

Change-Id: Iadbc9af0476009f2d43ecdd3d8f1335f31a04446
Reviewed-by: Assam Boudjelthia <assam.boudjelthia@qt.io>
This commit is contained in:
Volker Hilsheimer 2023-11-24 10:07:35 +01:00
parent 9e6c9eda6f
commit c5ba3ac95c
1 changed files with 5 additions and 54 deletions
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59
src/corelib/kernel/qjniobject.cpp
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@ -281,16 +281,10 @@ using namespace Qt::StringLiterals;
class QJniObjectPrivate
{
public:
// The JNIEnv is attached to the current thread, and the pointer remains
// valid for as long as the thread is alive. If the QJniObject were to
// outlive the thread that it lives in, and gets called for anything other
// than destruction, then we have a data race anyway.
QJniObjectPrivate()
: m_env(QJniEnvironment::getJniEnv())
{
}
~QJniObjectPrivate() {
// use the environment of the current thread here
JNIEnv *env = QJniEnvironment::getJniEnv();
if (m_jobject)
env->DeleteGlobalRef(m_jobject);
@ -298,16 +292,11 @@ public:
env->DeleteGlobalRef(m_jclass);
}
JNIEnv *jniEnv() const noexcept
{
return m_env;
}
template <typename ...Args>
void construct(const char *signature = nullptr, Args &&...args)
{
if (m_jclass) {
JNIEnv *env = jniEnv();
JNIEnv *env = QJniEnvironment::getJniEnv();
// get default constructor
jmethodID constructorId = QJniObject::getCachedMethodID(env, m_jclass, m_className, "<init>",
signature ? signature : "()V");
@ -326,7 +315,6 @@ public:
}
QByteArray m_className;
JNIEnv * const m_env;
jobject m_jobject = nullptr;
jclass m_jclass = nullptr;
bool m_own_jclass = true;
@ -706,7 +694,7 @@ QJniObject::QJniObject(jobject object)
if (!object)
return;
JNIEnv *env = d->jniEnv();
JNIEnv *env = QJniEnvironment::getJniEnv();
d->m_jobject = env->NewGlobalRef(object);
jclass cls = env->GetObjectClass(object);
d->m_jclass = static_cast<jclass>(env->NewGlobalRef(cls));
@ -758,48 +746,11 @@ QByteArray getClassNameHelper(JNIEnv *env, const QJniObjectPrivate *d)
/*! \internal
While we can synchronize concurrent access to a QJniObject on the C++ side,
we cannot synchronize access across C++ and Java, so any concurrent access to
a QJniObject, except the most basic ref-counting operations (destructor and
assignment) is dangerous, and all calls should happen from the thread that
created the Java object.
However, we have code in Qt that does that, so we use a cheap approach to check
for the condition and fall back to the thread-local JNI environment. We do not
re-attach to the thread though - that must have been done when constructing this
QJniObject.
Returns the JNIEnv of the calling thread.
*/
JNIEnv *QJniObject::jniEnv() const noexcept
{
JNIEnv *env = nullptr;
const bool threadCheck = [this, &env]{
JavaVM *vm = QtAndroidPrivate::javaVM();
const jint ret = vm->GetEnv((void**)&env, JNI_VERSION_1_6);
if (ret == JNI_EDETACHED) {
qCCritical(lcJniThreadCheck) << "The JNI Environment has been detached from its Java "
"thread!";
return false;
} else if (ret != JNI_OK) {
qCCritical(lcJniThreadCheck) << "An error occurred while acquiring JNI environment!";
return false;
}
if (env != d->jniEnv()) {
qCCritical(lcJniThreadCheck) << "JNI Environment mismatch - probably accessing this "
"Java object from the wrong thread!";
return false;
}
return true;
}();
if (!threadCheck) {
if (!env) {
qFatal() << "No JNI environment attached to" << QThread::currentThread();
} else {
qCCritical(lcJniThreadCheck) << "JNI threading error when calling object of type"
<< getClassNameHelper(env, d.get()) << "from thread"
<< QThread::currentThread();
}
}
return env;
return QJniEnvironment::getJniEnv();
}
/*!
@ -1467,7 +1418,7 @@ void QJniObject::assign(jobject obj)
d = QSharedPointer<QJniObjectPrivate>::create();
if (obj) {
JNIEnv *env = d->jniEnv();
JNIEnv *env = QJniEnvironment::getJniEnv();
d->m_jobject = env->NewGlobalRef(obj);
jclass objectClass = env->GetObjectClass(obj);
d->m_jclass = static_cast<jclass>(env->NewGlobalRef(objectClass));