Android開發進階之NIO非阻塞包(七)

今天我們繼續就android DDMS源碼一起分析NIO非阻塞通訊方式，android123也會給大家分享下手機和PC互通中的一些技術。在NIO中有關SocketChannel和ByteBuffer的使用細節，可以在今天文章中

static void read(SocketChannel chan, byte[] data, int length, int timeout)
throws TimeoutException, IOException {
ByteBuffer buf = ByteBuffer.wrap(data, 0, length != -1 ? length : data.length); //從字節數組中實例化ByteBuffer
int numWaits = 0;

while (buf.position() != buf.limit()) { //循環接收數據
int count;

count = chan.read(buf);
if (count < 0) {
throw new IOException("EOF"); //讀到末尾
} else if (count == 0) {
if (timeout != 0 && numWaits * WAIT_TIME > timeout) {
throw new TimeoutException();
}
try {
Thread.sleep(WAIT_TIME);
} catch (InterruptedException IE) {
}
numWaits++;
} else {
numWaits = 0;
}
}
}

有關SocketChannel的寫操作，就是發送數據代碼如下:

static void write(SocketChannel chan, byte[] data, int length, int timeout)
throws TimeoutException, IOException {
ByteBuffer buf = ByteBuffer.wrap(data, 0, length != -1 ? length : data.length);
int numWaits = 0;

while (buf.position() != buf.limit()) {
int count;

count = chan.write(buf); //發送數據從ByteBuffer中
if (count < 0) {
throw new IOException("channel EOF");
} else if (count == 0) {
if (timeout != 0 && numWaits * WAIT_TIME > timeout) {
throw new TimeoutException();
}
try {
Thread.sleep(WAIT_TIME);
} catch (InterruptedException IE) {
}
numWaits++;
} else {
numWaits = 0;
}
}
}

有關ADB如何選擇一個具體的設備，可以使用 setDevice 方法，這樣當電腦中有模擬器或鏈接了多個手機，可以通過設備序列號，選擇需要通訊的設備。

static void setDevice(SocketChannel adbChan, IDevice device)
throws TimeoutException, AdbCommandRejectedException, IOException {
// if the device is not -1, then we first tell adb we're looking to talk
// to a specific device
if (device != null) {
String msg = "host:transport:" + device.getSerialNumber(); // 最後的獲取序列號，android123提示大家在adb命令中是adb get-serialno

byte[] device_query = formAdbRequest(msg);

write(adbChan, device_query);

AdbResponse resp = readAdbResponse(adbChan, false /* readDiagString */);
if (resp.okay == false) {
throw new AdbCommandRejectedException(resp.message,
true/*errorDuringDeviceSelection*/);
}
}
}

通過PC控制手機重啟的代碼，當然這裡需要Root權限才能執行

public static void reboot(String into, InetSocketAddress adbSockAddr,
Device device) throws TimeoutException, AdbCommandRejectedException, IOException {
byte[] request;
if (into == null) {
request = formAdbRequest("reboot:"); //$NON-NLS-1$
} else {
request = formAdbRequest("reboot:" + into); //$NON-NLS-1$
}

SocketChannel adbChan = null;
try {
adbChan = SocketChannel.open(adbSockAddr);
adbChan.configureBlocking(false);

// if the device is not -1, then we first tell adb we're looking to talk
// to a specific device
setDevice(adbChan, device);

write(adbChan, request);
} finally {
if (adbChan != null) {
adbChan.close();
}
}
}

我們可以看到基本上，每個命令的執行，都是用了單獨SocketChannel通過非阻塞方式執行，這樣大大加強了並發，所以DDMS可以一邊處理Logcat打印，顯示堆信息，處理文件管理等等，有關NIO服務器的內容，android開發網將著重分析MonitorThread.Java這個文件，一起說下NIO的框架。