Android helper functions.

Two helper functions to help developers to easily run C++ code on Android UI thread.

utils/README.md

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+#Android helper functions
+
+Two helper functions to help developers to easily run C++ code on Android UI thread.
+
+Check https://www.kdab.com/qt-on-android-how-to-run-c-code-on-android-ui-thread to learn more about this functions.
+

utils/android/src/com/kdab/android/utils/Runnable.java

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+package com.kdab.android.utils;
+
+class Runnable implements java.lang.Runnable
+{
+    @Override
+    public void run() {
+        runPendingCppRunnables();
+    }
+
+    public static native void runPendingCppRunnables();
+}

utils/androidutils.cpp

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+#include "androidutils.h"
+
+#include <deque>
+#include <memory>
+#include <mutex>
+
+#include <QtAndroid>
+#include <QSemaphore>
+#include <QAndroidJniEnvironment>
+
+namespace KDAB {
+namespace Android {
+
+static std::deque<Runnable> s_pendingRunnables;
+static std::mutex s_pendingRunnablesMutex;
+
+void runOnAndroidThread(const Runnable &runnable)
+{
+    s_pendingRunnablesMutex.lock();
+    bool triggerRun = s_pendingRunnables.empty();
+    s_pendingRunnables.push_back(runnable);
+    s_pendingRunnablesMutex.unlock();
+    if (triggerRun) {
+        QtAndroid::androidActivity().callMethod<void>("runOnUiThread",
+                                                      "(Ljava/lang/Runnable;)V",
+                                                      QAndroidJniObject("com/kdab/android/utils/Runnable").object());
+    }
+}
+
+void runOnAndroidThreadSync(const Runnable &runnable, int waitMs)
+{
+    std::shared_ptr<QSemaphore> sem = std::make_shared<QSemaphore>();
+    runOnAndroidThread([sem, &runnable](){
+        runnable();
+        sem->release();
+    });
+    sem->tryAcquire(1, waitMs);
+}
+
+extern "C" JNIEXPORT void JNICALL Java_com_kdab_android_utils_Runnable_runPendingCppRunnables(JNIEnv */*env*/, jobject /*obj*/)
+{
+    for (;;) { // run all posted runnables
+        s_pendingRunnablesMutex.lock();
+        if (s_pendingRunnables.empty()) {
+            s_pendingRunnablesMutex.unlock();
+            break;
+        }
+        Runnable runnable(std::move(s_pendingRunnables.front()));
+        s_pendingRunnables.pop_front();
+        s_pendingRunnablesMutex.unlock();
+        runnable();
+    }
+}
+
+} // namespace Android
+} // KDAB

utils/androidutils.h

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+#ifndef ANDROIDUTILS_H
+#define ANDROIDUTILS_H
+
+#include <functional>
+
+namespace KDAB {
+namespace Android {
+
+typedef std::function<void()> Runnable;
+
+/// Posts a runnable on Android thread, then exists.
+/// If you call runOnAndroidThread from Android UI thread,
+/// it will execute the runnable immediately
+void runOnAndroidThread(const Runnable &runnable);
+
+/// Posts a runnable on Android thread then waits until it's executed.
+void runOnAndroidThreadSync(const Runnable &runnable, int waitMs = INT_MAX);
+
+} // namespace Android
+} // KDAB
+
+#endif // ANDROIDUTILS_H