Add new glue code for writing native apps.

This factors out the boiler-plate code from the sample
app to a common glue code that can be used for everyone
writing this style of app: a dedicated app thread that
takes care of waiting for events and processing them.

As part of doing this, ALooper has a new facility to allow
registration of fds that cause ALooper_pollOnce() to return
the fd that has data, allowing the app to drive the loop
without callbacks.  Hopefully this makes some people feel better. :)

Also do some other cleanup of the ALooper API, plus some
actual documentation.

Change-Id: Ic53bd56bdf627e3ba28a3c093faa06a92be522b8

7 files changed, 621 insertions, 14 deletions

diff --git a/native/android/input.cpp b/native/android/input.cpp
index 015a1ce..89d53e2 100644
--- a/native/android/input.cpp
+++ b/native/android/input.cpp
@@ -186,9 +186,9 @@ float AMotionEvent_getHistoricalSize(AInputEvent* motion_event, size_t pointer_i
 }
 
 void AInputQueue_attachLooper(AInputQueue* queue, ALooper* looper,
-        ALooper_callbackFunc callback, void* data) {
+        ALooper_callbackFunc* callback, void* data) {
     queue->setPollLoop(static_cast<android::PollLoop*>(looper));
-    ALooper_setCallback(looper, queue->getConsumer().getChannel()->getReceivePipeFd(),
+    ALooper_addFd(looper, queue->getConsumer().getChannel()->getReceivePipeFd(),
             POLLIN, callback, data);
 }
 
diff --git a/native/android/looper.cpp b/native/android/looper.cpp
index 6e78bbd..1564c47 100644
--- a/native/android/looper.cpp
+++ b/native/android/looper.cpp
@@ -27,22 +27,41 @@ ALooper* ALooper_forThread() {
     return PollLoop::getForThread().get();
 }
 
-ALooper* ALooper_prepare() {
+ALooper* ALooper_prepare(int32_t opts) {
+    bool allowFds = (opts&ALOOPER_PREPARE_ALLOW_NON_CALLBACKS) != 0;
     sp<PollLoop> loop = PollLoop::getForThread();
     if (loop == NULL) {
-        loop = new PollLoop();
+        loop = new PollLoop(allowFds);
         PollLoop::setForThread(loop);
     }
+    if (loop->getAllowNonCallbacks() != allowFds) {
+        LOGW("ALooper_prepare again with different ALOOPER_PREPARE_ALLOW_NON_CALLBACKS");
+    }
     return loop.get();
 }
 
-int32_t ALooper_pollOnce(int timeoutMillis) {
+int32_t ALooper_pollOnce(int timeoutMillis, int* outEvents, void** outData) {
     sp<PollLoop> loop = PollLoop::getForThread();
     if (loop == NULL) {
         LOGW("ALooper_pollOnce: No looper for this thread!");
         return -1;
     }
-    return loop->pollOnce(timeoutMillis) ? 1 : 0;
+    return loop->pollOnce(timeoutMillis, outEvents, outData);
+}
+
+int32_t ALooper_pollAll(int timeoutMillis, int* outEvents, void** outData) {
+    sp<PollLoop> loop = PollLoop::getForThread();
+    if (loop == NULL) {
+        LOGW("ALooper_pollOnce: No looper for this thread!");
+        return -1;
+    }
+    
+    int32_t result;
+    while ((result = loop->pollOnce(timeoutMillis, outEvents, outData)) == ALOOPER_POLL_CALLBACK) {
+        ;
+    }
+    
+    return result;
 }
 
 void ALooper_acquire(ALooper* looper) {
@@ -53,11 +72,11 @@ void ALooper_release(ALooper* looper) {
     static_cast<PollLoop*>(looper)->decStrong((void*)ALooper_acquire);
 }
 
-void ALooper_setCallback(ALooper* looper, int fd, int events,
+void ALooper_addFd(ALooper* looper, int fd, int events,
         ALooper_callbackFunc* callback, void* data) {
     static_cast<PollLoop*>(looper)->setLooperCallback(fd, events, callback, data);
 }
 
-int32_t ALooper_removeCallback(ALooper* looper, int fd) {
+int32_t ALooper_removeFd(ALooper* looper, int fd) {
     return static_cast<PollLoop*>(looper)->removeCallback(fd) ? 1 : 0;
 }
diff --git a/native/glue/threaded_app/Android.mk b/native/glue/threaded_app/Android.mk
new file mode 100644
index 0000000..cfc9b2a
--- /dev/null
+++ b/native/glue/threaded_app/Android.mk
@@ -0,0 +1,18 @@
+BASE_PATH := $(call my-dir)
+LOCAL_PATH:= $(call my-dir)
+
+include $(CLEAR_VARS)
+
+# our source files
+#
+LOCAL_SRC_FILES:= \
+    threaded_app.c
+
+LOCAL_C_INCLUDES += \
+    frameworks/base/native/include \
+    frameworks/base/core/jni/android \
+    dalvik/libnativehelper/include/nativehelper
+
+LOCAL_MODULE:= libthreaded_app
+
+include $(BUILD_STATIC_LIBRARY)
diff --git a/native/glue/threaded_app/threaded_app.c b/native/glue/threaded_app/threaded_app.c
new file mode 100644
index 0000000..c9cae8b
--- /dev/null
+++ b/native/glue/threaded_app/threaded_app.c
@@ -0,0 +1,275 @@
+/*
+ * Copyright (C) 2010 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <jni.h>
+
+#include <errno.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/resource.h>
+
+#include <android_glue/threaded_app.h>
+
+#include <android/log.h>
+
+#define LOGI(...) ((void)__android_log_print(ANDROID_LOG_INFO, "threaded_app", __VA_ARGS__))
+#define LOGW(...) ((void)__android_log_print(ANDROID_LOG_WARN, "threaded_app", __VA_ARGS__))
+
+void android_app_destroy(struct android_app* android_app) {
+    LOGI("android_app_destroy!");
+    pthread_mutex_lock(&android_app->mutex);
+    if (android_app->inputQueue != NULL) {
+        AInputQueue_detachLooper(android_app->inputQueue);
+    }
+    android_app->destroyed = 1;
+    pthread_cond_broadcast(&android_app->cond);
+    pthread_mutex_unlock(&android_app->mutex);
+    // Can't touch android_app object after this.
+}
+
+int8_t android_app_read_cmd(struct android_app* android_app) {
+    int8_t cmd;
+    if (read(android_app->msgread, &cmd, sizeof(cmd)) == sizeof(cmd)) {
+        return cmd;
+    } else {
+        LOGW("No data on command pipe!");
+    }
+    return -1;
+}
+
+void android_app_exec_cmd(struct android_app* android_app, int8_t cmd) {
+    switch (cmd) {
+        case APP_CMD_INPUT_CHANGED:
+            LOGI("APP_CMD_INPUT_CHANGED\n");
+            pthread_mutex_lock(&android_app->mutex);
+            if (android_app->inputQueue != NULL) {
+                AInputQueue_detachLooper(android_app->inputQueue);
+            }
+            android_app->inputQueue = android_app->pendingInputQueue;
+            if (android_app->inputQueue != NULL) {
+                LOGI("Attaching input queue to looper");
+                AInputQueue_attachLooper(android_app->inputQueue,
+                        android_app->looper, NULL, (void*)LOOPER_ID_EVENT);
+            }
+            pthread_cond_broadcast(&android_app->cond);
+            pthread_mutex_unlock(&android_app->mutex);
+            break;
+
+        case APP_CMD_WINDOW_CHANGED:
+            LOGI("APP_CMD_WINDOW_CHANGED\n");
+            pthread_mutex_lock(&android_app->mutex);
+            android_app->window = android_app->pendingWindow;
+            pthread_cond_broadcast(&android_app->cond);
+            pthread_mutex_unlock(&android_app->mutex);
+            break;
+
+        case APP_CMD_START:
+        case APP_CMD_RESUME:
+        case APP_CMD_PAUSE:
+        case APP_CMD_STOP:
+            LOGI("activityState=%d\n", cmd);
+            pthread_mutex_lock(&android_app->mutex);
+            android_app->activityState = cmd;
+            pthread_cond_broadcast(&android_app->cond);
+            pthread_mutex_unlock(&android_app->mutex);
+            break;
+            
+        case APP_CMD_DESTROY:
+            LOGI("APP_CMD_DESTROY\n");
+            android_app->destroyRequested = 1;
+            break;
+    }
+}
+
+static void* android_app_entry(void* param) {
+    struct android_app* android_app = (struct android_app*)param;
+    
+    ALooper* looper = ALooper_prepare(ALOOPER_PREPARE_ALLOW_NON_CALLBACKS);
+    ALooper_addFd(looper, android_app->msgread, POLLIN, NULL, (void*)LOOPER_ID_MAIN);
+    android_app->looper = looper;
+    
+    pthread_mutex_lock(&android_app->mutex);
+    android_app->running = 1;
+    pthread_cond_broadcast(&android_app->cond);
+    pthread_mutex_unlock(&android_app->mutex);
+    
+    android_main(android_app);
+    return NULL;
+}
+
+// --------------------------------------------------------------------
+// Native activity interaction (called from main thread)
+// --------------------------------------------------------------------
+
+static struct android_app* android_app_create(ANativeActivity* activity) {
+    struct android_app* android_app = (struct android_app*)malloc(sizeof(struct android_app));
+    memset(android_app, 0, sizeof(struct android_app));
+    android_app->activity = activity;
+    
+    pthread_mutex_init(&android_app->mutex, NULL);
+    pthread_cond_init(&android_app->cond, NULL);
+    
+    int msgpipe[2];
+    if (pipe(msgpipe)) {
+        LOGI("could not create pipe: %s", strerror(errno));
+    }
+    android_app->msgread = msgpipe[0];
+    android_app->msgwrite = msgpipe[1];
+    
+    pthread_attr_t attr; 
+    pthread_attr_init(&attr);
+    pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
+    pthread_create(&android_app->thread, &attr, android_app_entry, android_app);
+    
+    // Wait for thread to start.
+    pthread_mutex_lock(&android_app->mutex);
+    while (!android_app->running) {
+        pthread_cond_wait(&android_app->cond, &android_app->mutex);
+    }
+    pthread_mutex_unlock(&android_app->mutex);
+    
+    return android_app;
+}
+
+static void android_app_write_cmd(struct android_app* android_app, int8_t cmd) {
+    if (write(android_app->msgwrite, &cmd, sizeof(cmd)) != sizeof(cmd)) {
+        LOGI("Failure writing android_app cmd: %s\n", strerror(errno));
+    }
+}
+
+static void android_app_set_input(struct android_app* android_app, AInputQueue* inputQueue) {
+    pthread_mutex_lock(&android_app->mutex);
+    android_app->pendingInputQueue = inputQueue;
+    android_app_write_cmd(android_app, APP_CMD_INPUT_CHANGED);
+    while (android_app->inputQueue != android_app->pendingInputQueue) {
+        pthread_cond_wait(&android_app->cond, &android_app->mutex);
+    }
+    pthread_mutex_unlock(&android_app->mutex);
+}
+
+static void android_app_set_window(struct android_app* android_app, ANativeWindow* window) {
+    pthread_mutex_lock(&android_app->mutex);
+    android_app->pendingWindow = window;
+    android_app_write_cmd(android_app, APP_CMD_WINDOW_CHANGED);
+    while (android_app->window != android_app->pendingWindow) {
+        pthread_cond_wait(&android_app->cond, &android_app->mutex);
+    }
+    pthread_mutex_unlock(&android_app->mutex);
+}
+
+static void android_app_set_activity_state(struct android_app* android_app, int8_t cmd) {
+    pthread_mutex_lock(&android_app->mutex);
+    android_app_write_cmd(android_app, cmd);
+    while (android_app->activityState != cmd) {
+        pthread_cond_wait(&android_app->cond, &android_app->mutex);
+    }
+    pthread_mutex_unlock(&android_app->mutex);
+}
+
+static void android_app_free(struct android_app* android_app) {
+    pthread_mutex_lock(&android_app->mutex);
+    android_app_write_cmd(android_app, APP_CMD_DESTROY);
+    while (!android_app->destroyed) {
+        pthread_cond_wait(&android_app->cond, &android_app->mutex);
+    }
+    pthread_mutex_unlock(&android_app->mutex);
+    
+    close(android_app->msgread);
+    close(android_app->msgwrite);
+    pthread_cond_destroy(&android_app->cond);
+    pthread_mutex_destroy(&android_app->mutex);
+    free(android_app);
+}
+
+static void onDestroy(ANativeActivity* activity) {
+    LOGI("Destroy: %p\n", activity);
+    android_app_free((struct android_app*)activity->instance);
+}
+
+static void onStart(ANativeActivity* activity) {
+    LOGI("Start: %p\n", activity);
+    android_app_set_activity_state((struct android_app*)activity->instance, APP_CMD_START);
+}
+
+static void onResume(ANativeActivity* activity) {
+    LOGI("Resume: %p\n", activity);
+    android_app_set_activity_state((struct android_app*)activity->instance, APP_CMD_RESUME);
+}
+
+static void* onSaveInstanceState(ANativeActivity* activity, size_t* outLen) {
+    LOGI("SaveInstanceState: %p\n", activity);
+    return NULL;
+}
+
+static void onPause(ANativeActivity* activity) {
+    LOGI("Pause: %p\n", activity);
+    android_app_set_activity_state((struct android_app*)activity->instance, APP_CMD_PAUSE);
+}
+
+static void onStop(ANativeActivity* activity) {
+    LOGI("Stop: %p\n", activity);
+    android_app_set_activity_state((struct android_app*)activity->instance, APP_CMD_STOP);
+}
+
+static void onLowMemory(ANativeActivity* activity) {
+    LOGI("LowMemory: %p\n", activity);
+}
+
+static void onWindowFocusChanged(ANativeActivity* activity, int focused) {
+    LOGI("WindowFocusChanged: %p -- %d\n", activity, focused);
+    android_app_write_cmd((struct android_app*)activity->instance,
+            focused ? APP_CMD_GAINED_FOCUS : APP_CMD_LOST_FOCUS);
+}
+
+static void onNativeWindowCreated(ANativeActivity* activity, ANativeWindow* window) {
+    LOGI("NativeWindowCreated: %p -- %p\n", activity, window);
+    android_app_set_window((struct android_app*)activity->instance, window);
+}
+
+static void onNativeWindowDestroyed(ANativeActivity* activity, ANativeWindow* window) {
+    LOGI("NativeWindowDestroyed: %p -- %p\n", activity, window);
+    android_app_set_window((struct android_app*)activity->instance, NULL);
+}
+
+static void onInputQueueCreated(ANativeActivity* activity, AInputQueue* queue) {
+    LOGI("InputQueueCreated: %p -- %p\n", activity, queue);
+    android_app_set_input((struct android_app*)activity->instance, queue);
+}
+
+static void onInputQueueDestroyed(ANativeActivity* activity, AInputQueue* queue) {
+    LOGI("InputQueueDestroyed: %p -- %p\n", activity, queue);
+    android_app_set_input((struct android_app*)activity->instance, NULL);
+}
+
+void ANativeActivity_onCreate(ANativeActivity* activity,
+        void* savedState, size_t savedStateSize) {
+    LOGI("Creating: %p\n", activity);
+    activity->callbacks->onDestroy = onDestroy;
+    activity->callbacks->onStart = onStart;
+    activity->callbacks->onResume = onResume;
+    activity->callbacks->onSaveInstanceState = onSaveInstanceState;
+    activity->callbacks->onPause = onPause;
+    activity->callbacks->onStop = onStop;
+    activity->callbacks->onLowMemory = onLowMemory;
+    activity->callbacks->onWindowFocusChanged = onWindowFocusChanged;
+    activity->callbacks->onNativeWindowCreated = onNativeWindowCreated;
+    activity->callbacks->onNativeWindowDestroyed = onNativeWindowDestroyed;
+    activity->callbacks->onInputQueueCreated = onInputQueueCreated;
+    activity->callbacks->onInputQueueDestroyed = onInputQueueDestroyed;
+    
+    activity->instance = android_app_create(activity);
+}
diff --git a/native/include/android/input.h b/native/include/android/input.h
index 75be85a..014b6a3 100644
--- a/native/include/android/input.h
+++ b/native/include/android/input.h
@@ -534,10 +534,11 @@ struct AInputQueue;
 typedef struct AInputQueue AInputQueue;
 
 /*
- * Add this input queue to a looper for processing.
+ * Add this input queue to a looper for processing.  See
+ * ALooper_addFd() for information on the callback and data params.
  */
 void AInputQueue_attachLooper(AInputQueue* queue, ALooper* looper,
-        ALooper_callbackFunc callback, void* data);
+        ALooper_callbackFunc* callback, void* data);
 
 /*
  * Remove the input queue from the looper it is currently attached to.
diff --git a/native/include/android/looper.h b/native/include/android/looper.h
index 90a8983..2917216 100644
--- a/native/include/android/looper.h
+++ b/native/include/android/looper.h
@@ -24,25 +24,151 @@
 extern "C" {
 #endif
 
+/**
+ * ALooper
+ *
+ * A looper is the state tracking an event loop for a thread.
+ * Loopers do not define event structures or other such things; rather
+ * they are a lower-level facility to attach one or more discrete objects
+ * listening for an event.  An "event" here is simply data available on
+ * a file descriptor: each attached object has an associated file descriptor,
+ * and waiting for "events" means (internally) polling on all of these file
+ * descriptors until one or more of them have data available.
+ *
+ * A thread can have only one ALooper associated with it.
+ */
 struct ALooper;
 typedef struct ALooper ALooper;
 
+/**
+ * For callback-based event loops, this is the prototype of the function
+ * that is called.  It is given the file descriptor it is associated with,
+ * a bitmask of the poll events that were triggered (typically POLLIN), and
+ * the data pointer that was originally supplied.
+ *
+ * Implementations should return 1 to continue receiving callbacks, or 0
+ * to have this file descriptor and callback unregistered from the looper.
+ */
 typedef int ALooper_callbackFunc(int fd, int events, void* data);
 
+/**
+ * Return the ALooper associated with the calling thread, or NULL if
+ * there is not one.
+ */
 ALooper* ALooper_forThread();
 
-ALooper* ALooper_prepare();
+enum {
+    /**
+     * Option for ALooper_prepare: this ALooper will accept calls to
+     * ALooper_addFd() that do not have a callback (that is provide NULL
+     * for the callback).  In this case the caller of ALooper_pollOnce()
+     * or ALooper_pollAll() MUST check the return from these functions to
+     * discover when data is available on such fds and process it.
+     */
+    ALOOPER_PREPARE_ALLOW_NON_CALLBACKS = 1<<0
+};
 
-int32_t ALooper_pollOnce(int timeoutMillis);
+/**
+ * Prepare an ALooper associated with the calling thread, and return it.
+ * If the thread already has an ALooper, it is returned.  Otherwise, a new
+ * one is created, associated with the thread, and returned.
+ *
+ * The opts may be ALOOPER_PREPARE_ALLOW_NON_CALLBACKS or 0.
+ */
+ALooper* ALooper_prepare(int32_t opts);
+
+enum {
+    /**
+     * Result from ALooper_pollOnce() and ALooper_pollAll(): one or
+     * more callbacks were executed.
+     */
+    ALOOPER_POLL_CALLBACK = -1,
+    
+    /**
+     * Result from ALooper_pollOnce() and ALooper_pollAll(): the
+     * timeout expired.
+     */
+    ALOOPER_POLL_TIMEOUT = -2,
+    
+    /**
+     * Result from ALooper_pollOnce() and ALooper_pollAll(): an error
+     * occurred.
+     */
+    ALOOPER_POLL_ERROR = -3,
+};
 
+/**
+ * Wait for events to be available, with optional timeout in milliseconds.
+ * Invokes callbacks for all file descriptors on which an event occurred.
+ *
+ * If the timeout is zero, returns immediately without blocking.
+ * If the timeout is negative, waits indefinitely until an event appears.
+ *
+ * Returns ALOOPER_POLL_CALLBACK if a callback was invoked.
+ *
+ * Returns ALOOPER_POLL_TIMEOUT if there was no data before the given
+ * timeout expired.
+ *
+ * Returns ALOPER_POLL_ERROR if an error occurred.
+ *
+ * Returns a value >= 0 containing a file descriptor if it has data
+ * and it has no callback function (requiring the caller here to handle it).
+ * In this (and only this) case outEvents and outData will contain the poll
+ * events and data associated with the fd.
+ *
+ * This method does not return until it has finished invoking the appropriate callbacks
+ * for all file descriptors that were signalled.
+ */
+int32_t ALooper_pollOnce(int timeoutMillis, int* outEvents, void** outData);
+
+/**
+ * Like ALooper_pollOnce(), but performs all pending callbacks until all
+ * data has been consumed or a file descriptor is available with no callback.
+ * This function will never return ALOOPER_POLL_CALLBACK.
+ */
+int32_t ALooper_pollAll(int timeoutMillis, int* outEvents, void** outData);
+
+/**
+ * Acquire a reference on the given ALooper object.  This prevents the object
+ * from being deleted until the reference is removed.  This is only needed
+ * to safely hand an ALooper from one thread to another.
+ */
 void ALooper_acquire(ALooper* looper);
 
+/**
+ * Remove a reference that was previously acquired with ALooper_acquire().
+ */
 void ALooper_release(ALooper* looper);
 
-void ALooper_setCallback(ALooper* looper, int fd, int events,
+/**
+ * Add a new file descriptor to be polled by the looper.  If the same file
+ * descriptor was previously added, it is replaced.
+ *
+ * "fd" is the file descriptor to be added.
+ * "events" are the poll events to wake up on.  Typically this is POLLIN.
+ * "callback" is the function to call when there is an event on the file
+ * descriptor.
+ * "id" is an identifier to associated with this file descriptor, or 0.
+ * "data" is a private data pointer to supply to the callback.
+ *
+ * There are two main uses of this function:
+ *
+ * (1) If "callback" is non-NULL, then
+ * this function will be called when there is data on the file descriptor.  It
+ * should execute any events it has pending, appropriately reading from the
+ * file descriptor.
+ *
+ * (2) If "callback" is NULL, the fd will be returned by ALooper_pollOnce
+ * when it has data available, requiring the caller to take care of processing
+ * it.
+ */
+void ALooper_addFd(ALooper* looper, int fd, int events,
         ALooper_callbackFunc* callback, void* data);
 
-int32_t ALooper_removeCallback(ALooper* looper, int fd);
+/**
+ * Remove a previously added file descriptor from the looper.
+ */
+int32_t ALooper_removeFd(ALooper* looper, int fd);
 
 #ifdef __cplusplus
 };
diff --git a/native/include/android_glue/threaded_app.h b/native/include/android_glue/threaded_app.h
new file mode 100644
index 0000000..80de3bf
--- /dev/null
+++ b/native/include/android_glue/threaded_app.h
@@ -0,0 +1,168 @@
+/*
+ * Copyright (C) 2010 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <poll.h>
+#include <pthread.h>
+#include <sched.h>
+
+#include <android/native_activity.h>
+#include <android/looper.h>
+
+/**
+ * This is the interface for the standard glue code of a threaded
+ * application.  In this model, the application's code is running
+ * in its own thread separate from the main thread of the process.
+ * It is not required that this thread be associated with the Java
+ * VM, although it will need to be in order to make JNI calls any
+ * Java objects.
+ */
+struct android_app {
+    // The application can place a pointer to its own state object
+    // here if it likes.
+    void* userData;
+
+    // The ANativeActivity object instance that this app is running in.
+    ANativeActivity* activity;
+
+    // The ALooper associated with the app's thread.
+    ALooper* looper;
+
+    // When non-NULL, this is the input queue from which the app will
+    // receive user input events.
+    AInputQueue* inputQueue;
+
+    // When non-NULL, this is the window surface that the app can draw in.
+    ANativeWindow* window;
+
+    // Current state of the app's activity.  May be either APP_CMD_START,
+    // APP_CMD_RESUME, APP_CMD_PAUSE, or APP_CMD_STOP; see below.
+    int activityState;
+
+    // This is non-zero when the application's NativeActivity is being
+    // destroyed and waiting for the app thread to complete.
+    int destroyRequested;
+
+    // -------------------------------------------------
+    // Below are "private" implementation of the glue code.
+
+    pthread_mutex_t mutex;
+    pthread_cond_t cond;
+
+    int msgread;
+    int msgwrite;
+
+    pthread_t thread;
+
+    int running;
+    int destroyed;
+    AInputQueue* pendingInputQueue;
+    ANativeWindow* pendingWindow;
+};
+
+enum {
+    /**
+     * Looper data ID of commands coming from the app's main thread.
+     * These can be retrieved and processed with android_app_read_cmd()
+     * and android_app_exec_cmd().
+     */
+    LOOPER_ID_MAIN = 1,
+
+    /**
+     * Looper data ID of events coming from the AInputQueue of the
+     * application's window.  These can be read via the inputQueue
+     * object of android_app.
+     */
+    LOOPER_ID_EVENT = 2
+};
+
+enum {
+    /**
+     * Command from main thread: the AInputQueue has changed.  Upon processing
+     * this command, android_app->inputQueue will be updated to the new queue
+     * (or NULL).
+     */
+    APP_CMD_INPUT_CHANGED,
+
+    /**
+     * Command from main thread: the ANativeWindow has changed.  Upon processing
+     * this command, android_app->window will be updated to the new window surface
+     * (or NULL).
+     */
+    APP_CMD_WINDOW_CHANGED,
+
+    /**
+     * Command from main thread: the app's activity window has gained
+     * input focus.
+     */
+    APP_CMD_GAINED_FOCUS,
+
+    /**
+     * Command from main thread: the app's activity window has lost
+     * input focus.
+     */
+    APP_CMD_LOST_FOCUS,
+
+    /**
+     * Command from main thread: the app's activity has been started.
+     */
+    APP_CMD_START,
+
+    /**
+     * Command from main thread: the app's activity has been resumed.
+     */
+    APP_CMD_RESUME,
+
+    /**
+     * Command from main thread: the app's activity has been paused.
+     */
+    APP_CMD_PAUSE,
+
+    /**
+     * Command from main thread: the app's activity has been stopped.
+     */
+    APP_CMD_STOP,
+
+    /**
+     * Command from main thread: the app's activity is being destroyed,
+     * and waiting for the app thread to clean up and exit before proceeding.
+     */
+    APP_CMD_DESTROY,
+};
+
+/**
+ * Call if android_app->destroyRequested is non-zero.  Upon return, the
+ * android_app structure is no longer valid and must not be touched.
+ */
+void android_app_destroy(struct android_app* android_app);
+
+/**
+ * Call when ALooper_pollAll() returns LOOPER_ID_MAIN, reading the next
+ * app command message.
+ */
+int8_t android_app_read_cmd(struct android_app* android_app);
+
+/**
+ * Call with the command returned by android_app_read_cmd() to do the
+ * default processing of the given command.
+ */
+void android_app_exec_cmd(struct android_app* android_app, int8_t cmd);
+
+/**
+ * This is the function that application code must implement, representing
+ * the main entry to the app.
+ */
+extern void android_main(struct android_app* app);