Android/DalvikVM 如何处理 Handler?
我想知道 Android/DalvikVM 中如何处理处理程序。我正在为 Android 编写一个应用程序,在一个类中我有一个 Handler 方法,它从另一个类接收消息。 Handler 方法会充当线程并与同一类中的 run() 方法异步,还是会等到 run() 方法中的一行代码完成(某种原子操作)?或者其他什么?
我想知道,因为我想在 Handler 方法中将消息添加到队列中,并在 run() 方法中处理和删除它们(生产者-消费者)。
我的代码结构:
public class Parser implements Runnable {
public void run() {
while(true) {
// Remove a byte from the ring buffer and parse it
byte b = Ringbuffer_read();
// Parse
try {
Thread.sleep(40);
} catch (InterruptedException e) {}
}
}
private final Handler mHandler = new Handler() {
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case MESSAGE_READ:
// Store all the received bytes in the ring buffer
for (int i = 0; i < msg.arg1; i++) {
Ringbuffer_store(((byte[]) msg.obj)[i]);
}
break;
}
}
};
}
处理程序中的代码何时运行?它是否会在任何时候中断 run() 方法中的代码?我是否必须在 run() 和处理程序方法中的代码周围有一些同步或信号量或其他东西,这样我就不会损坏我的缓冲区?
I'm wondering how Handlers are processed in Android/DalvikVM. I'm writing an application for Android, and in one class I have a Handler method which receives messages from another class. Will the Handler method act as a Thread and be asynchronous to the run() method in the same class, or will it wait until a line of code in the run() method is finished (sort of atomic operation)? Or something else?
I'm wondering, because I want to add messages to a queue in the Handler method, and process and remove them in the run() method (producer-consumer).
My code structure:
public class Parser implements Runnable {
public void run() {
while(true) {
// Remove a byte from the ring buffer and parse it
byte b = Ringbuffer_read();
// Parse
try {
Thread.sleep(40);
} catch (InterruptedException e) {}
}
}
private final Handler mHandler = new Handler() {
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case MESSAGE_READ:
// Store all the received bytes in the ring buffer
for (int i = 0; i < msg.arg1; i++) {
Ringbuffer_store(((byte[]) msg.obj)[i]);
}
break;
}
}
};
}
When will the code in the handler run? Does it interrupt the code in the run() method at any point? Do I have to have some synchronization or semaphores or something around the code in the run() and handler method so that I don't corrupt my buffer?
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Android
Handler
将自身与创建它的任何线程相关联(假设该线程已经有一个循环程序)。默认情况下,Android 回调在名为“main”的线程上运行,该线程也称为 ui 线程。无论从哪个线程调用post
方法,handleMessage
方法都将从创建 Handler 的线程(通常是“主”线程)调用。因为handleMessage
方法总是在同一个线程中调用,所以一次只会处理一条消息。如果您的计划只有一个消费者,那么 Handler 是一个不错的选择。您不需要从消费者(处理程序)中删除消息,它们只需到达
handleMessage
进行处理即可。如果你想在“主”线程上进行处理,那么你只需创建一个新的处理程序,如果你想在后台进行处理以避免 ANR,你可能会想要使用 HandlerThread。下面是一个在它自己的后台线程上运行的处理程序的示例:请注意,在上面的描述中,类根本没有发挥作用,因为类是代码的结构方式,与代码在哪个线程上执行无关。
An Android
Handler
associates itself with whatever thread it is created in (assuming that thread has a looper already). By default in Android callbacks run on a thread named "main" which is also called the ui thread. Regardless of what thread thepost
method is called from thehandleMessage
method will be called from the thread that the Handler was created in (usually the "main" thread). Because thehandleMessage
method is always called in the same thread, only one message will be processed at a time.If your plan is to have only a single consumer then Handler is a good choice. You will not need to remove messages from your consumer (the Handler), instead they will simply arrive in
handleMessage
for processing. If you want to do processing on the "main" thread then you just make a new Handler, if you want to do processing in the background to avoid ANRs you will likely want to use HandlerThread. Here's an example of a Handler running on it's own background thread:Notice that in the description above class does not come into play at all because classes are how code is structured which is unrelated to what thread the code is executed on.