java线程和系统线程之间的关系是什么

时间:2014-02-11 08:02:50

标签: java android linux ipc

最近,我研究了Android系统中的Handler类。在我看来,Handler机制是Thread运行一个死循环并在该死循环中重复从队列中检索消息,然后将消息发送到目标处理程序。

但是当队列中没有消息时,必须在指定的时间内等待或阻塞线程,这可以减少CPU时间。我的理解是,为了在指定的时间内等待或阻止Thread,它使用linux epoll函数在本机层中等待指定的时间。然后,当队列中有消息时,它使用linux管道唤醒线程。

所以我的困惑是为什么Android系统使用Linux进程通信函数(IPC)来控制Java Thread 等待或唤醒? Java Thread与系统线程或linux线程之间的关系是什么?

换句话说,我真正想知道的是为什么android使用linux ipc函数来控制java线程来实现所谓的Handler,它用于在java线程之间发送消息。

以下是relevant code from the Android platform

public static void loop() {
        final Looper me = myLooper();
        if (me == null) {
            throw new RuntimeException("No Looper; Looper.prepare() wasn't called on this thread.");
        }
        final MessageQueue queue = me.mQueue;

        // Make sure the identity of this thread is that of the local process,
        // and keep track of what that identity token actually is.
        Binder.clearCallingIdentity();
        final long ident = Binder.clearCallingIdentity();

        for (;;) {
            Message msg = queue.next(); // might block
            if (msg == null) {
                // No message indicates that the message queue is quitting.
                return;
            }

            // This must be in a local variable, in case a UI event sets the logger
            Printer logging = me.mLogging;
            if (logging != null) {
                logging.println(">>>>> Dispatching to " + msg.target + " " +
                        msg.callback + ": " + msg.what);
            }

            msg.target.dispatchMessage(msg);

            if (logging != null) {
                logging.println("<<<<< Finished to " + msg.target + " " + msg.callback);
            }

            // Make sure that during the course of dispatching the
            // identity of the thread wasn't corrupted.
            final long newIdent = Binder.clearCallingIdentity();
            if (ident != newIdent) {
                Log.wtf(TAG, "Thread identity changed from 0x"
                        + Long.toHexString(ident) + " to 0x"
                        + Long.toHexString(newIdent) + " while dispatching to "
                        + msg.target.getClass().getName() + " "
                        + msg.callback + " what=" + msg.what);
            }

            msg.recycle();
        }
    }

1 个答案:

答案 0 :(得分:1)

在阅读完问题后,我的好奇心引导我this。我相信使用 Linux进程通信函数(IPC)来控制 Java线程存在误解。

我不相信我能更好地解释链接中给出的漂亮描述。

Communication Mechanism of Android Processes