Android process communication refers to the process of sharing information and completing tasks between multiple processes. Since the Android system is an operating system based on the Linux kernel and adopts a process-oriented architectural model, inter-process communication is an important part of its application development and the cornerstone to ensure information exchange and task collaboration between multiple processes.
Android process communication mainly consists of two methods, namely: based on Binder mechanism and based on Socket mechanism. Among them, the Binder mechanism is a common inter-process communication method in the Android system. Among these two communication mechanisms, the Android system provides a variety of analysis tools through which developers can monitor and debug process communications and detect problems in the communication process.
1. Binder-based process communication mechanism
Binder is a lightweight, efficient, stable and secure kernel-level inter-process communication (IPC) mechanism that supports inter-thread communication, inter-process communication and cross-process communication. Most Android system services are implemented on top of the Binder mechanism. The basic idea of the Binder mechanism to implement IPC is to create a Binder object for each process, and inter-process communication is achieved through the proxy and binding of the Binder object.
The three major components of the Binder mechanism
Binder driver, which is responsible for maintaining the Binder object in each process and providing underlying support for inter-process communication.
Binder proxy is an object that exists in the client process. It can call the method of the server process in the client process and obtain the return value of the server process.
Binder service, which is an object that exists in the server process, can accept call requests from clients and return the requests.
Binder communication process
Implement Binder agent/Binder service, use AIDL files to define communication interfaces (parameter types, return types, method names, etc.), and compile and implement corresponding Java classes through the aidl tool.
Establish a service connection (bindService) on the client and obtain the Binder object of the server through the IBinder interface.
The client initiates a Binder call to the server, and the Binder agent sends the call request to the Binder driver through Transaction. Transaction is an ordinary Java object of container type, used to encapsulate all transaction data.
The Binder driver receives the Transaction object from the Binder agent, packages it into a data packet, and transmits it to the service process.
The server receives the data packet through the Binder driver and packages the Transaction object and returns it to the Binder service class.
The Binder service class executes the request, encapsulates the return result into a Transaction object, and passes it to the Binder driver. The Binder driver sends it back to the client process, and is finally obtained by the Binder agent.
2. Process communication based on Socket
Socket is a common network communication technology, and Android also provides this communication technology for process communication. In Android, the Socket-based IPC method is mainly used for communication between different devices or different processes. In practical applications, TCP sockets are more common for communication.
TCP (Transmission Control Protocol) is a reliable transmission method that provides mechanisms such as block transmission, flow control, error control and congestion control. The TCP transmission mechanism establishes a connection through a three-way handshake to ensure reliable transmission of data.
Socket communication process
The client creates a socket locally through Socket and specifies the IP address and port number of the server.
The bottom layer connects to the server through Socket and successfully sends the connection request, and then enters the waiting state. The server successfully receives the connection request and returns a handle.
The client sends a request using the socket and receives a corresponding reply. This process is implemented in accordance with the TCP protocol.
After the server receives the client’s request, it generates a processing result based on the request content and sends it back to the client through the socket.
It should be noted that when using Socket communication, since there are no concepts of service proxy and service object, the client and server need to design their own communication protocol for communication. A common way is to use JSON or XML format for data interaction.
3. Monitoring and debugging of process communication
In order to ensure that inter-process communication can proceed normally, developers need to monitor and debug the process and data of process communication. The Android system provides a variety of tools to help developers monitor and diagnose problems.
Traceview – used to monitor the system calls and execution time of a program while it is running, and determine the running status of the current program by analyzing the call stack.
Profiler – can obtain the CPU and memory usage information of the process to help developers optimize the performance of applications, especially for I/O-intensive or network-intensive applications, which can effectively improve their throughput.
DDMS – A tool in Android debugging mode, used to remotely monitor the running status of applications, including detailed information during process communication, such as logs, thread status, memory, CPU and other information.
Systrace – an advanced analysis tool provided by the Android system, which can monitor call relationships and processes at the system level. Systrace can capture inter-process call relationships and display all events that occur in applications and the kernel.
When it comes to process communication, the security issues of cross-process communication need to be dealt with. Here is a simple code example that uses the Binder mechanism for secure cross-process communication.
Define the AIDL interface Define the AIDL interface between the client and the server for data exchange and definition of operation requests.
interface IMyService { int getResult(int a, int b); }
The server implements the AIDL interface on the server, implements the AIDL interface, and defines an IBinder interface to implement inter-process communication, while ensuring that the method requested by the client is executed in the thread pool defined on the server.
public class MyService extends Service {
private Binder mBinder;
private ExecutorService mExecutorService;
private IMyService.Stub mStub = new IMyService.Stub() {
@Override
public int getResult(int a, int b) throws RemoteException {
//
return a + b;
}
};
public MyService() {
mBinder = new Binder();
mExecutorService = Executors.newFixedThreadPool(2);
}
@Nullable
@Override
public IBinder onBind(Intent intent) {
return mBinder;
}
private class Binder extends IMyService.Stub {
@Override
public int getResult(final int a, final int b) throws RemoteException {
//
return mExecutorService.submit(new Callable<Integer>() {
@Override
public Integer call() throws Exception {
//
return a + b;
}
}).get();
}
}
}
The client starts the service and makes the call. The client needs to start the service and instantiate the service interface. Then it can call the AIDL method of the remote server.
public class MainActivity extends AppCompatActivity {
private IMyService mMyService;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//
Intent intent = new Intent(this, MyService.class);
bindService(intent, mConnection, BIND_AUTO_CREATE);
}
private ServiceConnection mConnection = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName name, IBinder binder) {
//
mMyService = IMyService.Stub.asInterface(binder);
try {
int result = mMyService.getResult(3, 4);
Log.d("TAG", "The result is " + result);
} catch (RemoteException e) {
e.printStackTrace();
}
}
@Override
public void onServiceDisconnected(ComponentName name) {
//
mMyService = null;
}
};
@Override
protected void onDestroy() {
super.onDestroy();
//
unbindService(mConnection);
}
}
In this example, the server defines the request processing method in the thread pool to avoid blocking the main process or other requests. This approach ensures that requests run better in a concurrent environment and ensures the security of server-side processing of requests. At the same time, the server also protects all user data of the application by ensuring the security of task execution data defined by itself.
Summarize
The process communication methods based on the Binder mechanism and the Socket mechanism in the Android system are important parts of Android application development. The Binder mechanism is a common inter-process communication method in the Android system. It can achieve efficient, stable and secure communication between processes. Socket is a common network communication technology that can be used for communication between different devices or different processes. Regardless of the form of process communication, the Android system provides a variety of tools to monitor and debug the communication process, helping developers track and analyze problems encountered during program operation, thereby continuously improving application performance and user experience. .