Why does the Android system use Binder as the IPC mechanism?

The Android system provides a variety of inter-process communication (IPC) mechanisms for data exchange and communication between different processes. The following are several commonly used IPC mechanisms in the Android system:

1. Intent: Intent is a commonly used inter-process communication method in the Android system. By sending Intent, data can be transferred and actions can be triggered between different application components. Intent can be used to start components such as Activity, Service, BroadcastReceiver, and can carry data for communication.
2. Binder: Binder is an inter-process communication (IPC) mechanism in the Android system, which is based on the C/S (Client/Server) model. Through Binder, a process can expose its services to other processes, and other processes can make remote calls through Binder. Binder provides functions such as cross-process method calls, data transmission, and thread synchronization.
3. ContentProvider: ContentProvider is an inter-process communication mechanism in the Android system, used to share data between different applications. Through ContentProvider, an application can expose its own data to other applications and provide operations for adding, deleting, modifying and querying data.
4. Messenger: Messenger is an inter-process communication mechanism based on Binder in the Android system. It uses Handler and Message to achieve inter-process communication. A process can pass its Handler object to other processes through Messenger, and other processes can send messages to the process through the Handler.
5. AIDL (Android Interface Definition Language): AIDL is an inter-process communication mechanism in the Android system, used to define the interface for cross-process communication. Through AIDL, an application can define its own interface and expose the interface to other applications, which can then make remote calls through AIDL.

IPC Mechanism

IPC (Inter-Process Communication) refers to the mechanism used in the operating system to achieve data transmission and sharing between different processes. It allows different processes to exchange information with each other during execution to achieve collaborative work.

Common IPC mechanisms include the following:

1. Pipe: Pipe is a half-duplex communication method that can transfer data between parent and child processes. Pipes can be anonymous or named.
2. Semaphore: A semaphore is a mechanism for synchronization and mutual exclusion between processes. It can be used to solve problems such as race conditions and deadlocks between processes.
3. Message Queue: A message queue is a mechanism for passing messages between processes. It allows senders to put messages into the queue and receivers to take messages out of the queue.
4. Shared Memory: Shared memory is a mechanism that allows multiple processes to access the same memory. Through shared memory, processes can directly read and write shared memory areas, thereby achieving efficient data exchange.
5. Socket: A socket is a mechanism for implementing network communication. It can transfer data between different hosts and implement inter-process communication.

Linux IPC Principles

Linux IPC (Inter-Process Communication) refers to the mechanism for data exchange and communication between different processes in the Linux operating system. It allows processes to share information, synchronize operations, and notify each other.

picture

Linux provides a variety of IPC mechanisms, including pipes, named pipes, signals, message queues, shared memory, and sockets.

• Pipe is a half-duplex communication method used to transfer data between parent and child processes or sibling processes. It is a communication method based on file descriptors, and data can only flow in one direction.
• A named pipe is a special file that enables communication between unrelated processes. It is similar to a pipe, but can be named through the file system, allowing communication between unrelated processes.
• Signal is an asynchronous communication mechanism used to pass simple messages between processes. A process can send a signal to other processes, and the receiving process can perform corresponding operations based on the type of signal.
• A message queue is a mechanism for communication through a buffer provided by the kernel. A process can send messages to a message queue, and other processes can read messages from the queue.
• Shared memory is a mechanism that maps a memory area to the address space of multiple processes. Multiple processes can directly access the shared memory, thereby achieving efficient data exchange.
• A socket is a network communication mechanism used for inter-process communication between different hosts. Sockets can be used for local inter-process communication (Unix domain sockets) or network inter-process communication (network sockets).

The general process of IPC communication:

1. Create an IPC object: First, the process needs to create an IPC object, such as a pipe, message queue, shared memory, or semaphore. This can be done by calling the corresponding system call function, such as pipe() to create a pipe, msgget() to create a message queue, shmget() to create shared memory, and semget() to create a semaphore.
2. Connecting IPC objects: After creating an IPC object, the process needs to connect to the object. For pipes, you can use the dup() or dup2() function to redirect standard input, output, or error to the read or write end of the pipe. For message queues, shared memory, and semaphores, you can use the corresponding system call functions to connect to the object, such as msgrcv() and msgsnd() for message queues, shmat() for shared memory, and semop() for semaphores.
3. Data exchange and sharing: After connecting to an IPC object, processes can exchange and share data by reading and writing pipes, sending and receiving messages, reading and writing shared memory, or operating semaphores. The specific operation method depends on the IPC method used.
4. Disconnect and delete IPC objects: When a process no longer needs to use an IPC object, it should disconnect from the object and delete the object to release resources. For pipes, you can close the corresponding file descriptor; for message queues, you can use the msgctl() function to delete the queue; for shared memory, you can use the shmdt() function to disconnect and the shmctl() function to delete the shared memory; for semaphores, you can use the semctl() function to delete the semaphore.

Some disadvantages of Linux IPC communication:

1. Complexity: IPC communication involves data transmission and synchronization between multiple processes, and requires the use of specific APIs and mechanisms. These APIs and mechanisms may be complex and require developers to have certain expertise and experience.
2. Performance overhead: IPC communication requires data transmission and synchronization between different processes, which will introduce certain performance overhead. For example, when using pipes or message queues, data replication and buffering are required, which may increase system load and latency.
3. Security: IPC communication may have security issues. For example, if the permissions or authentication mechanisms are not configured correctly, unauthorized processes may access shared resources or tamper with communication data.
4. Reliability: IPC communication may face reliability issues. For example, if a process crashes or terminates unexpectedly, it may cause communication interruption or data loss.
5. Cross-platform compatibility: Different operating systems may have different IPC mechanisms and APIs, which may result in additional work to ensure compatibility when developing across platforms.

Binder IPC Principle

In the Android system, in order to meet the special needs of mobile devices and to make up for the shortcomings of Linux IPC, some modifications and optimizations have been made to the Linux IPC mechanism.

On the one hand, Android introduced the Binder mechanism as the core mechanism for inter-process communication. The Binder mechanism is an efficient, message-based IPC mechanism that can provide better performance and security. Compared with Linux's traditional IPC mechanisms (such as pipes, message queues, shared memory, etc.), the Binder mechanism has lower latency and higher throughput, and can better meet the real-time requirements of mobile devices.

On the other hand, Android also introduces some specific IPC mechanisms, such as Intent and Broadcast. Intent is a mechanism for passing messages and data between different components, which can realize cross-process communication. Broadcast is a broadcast mechanism that allows different components in an application to communicate with each other. These mechanisms are widely used in the Android system and can easily realize interaction and data sharing between applications.

Although Android uses the Linux IPC mechanism, the IPC mechanism has been optimized and expanded to provide better performance and a more convenient development experience based on the special needs of mobile devices.

The Binder mechanism implements inter-process communication through the Binder driver, and communicates and exchanges data through the Binder object. It provides a convenient and efficient IPC mechanism and is one of the important components in the Android system. It allows different processes to communicate and exchange data. The IPC principle of Binder is as follows:

1. Binder driver: Binder driver is the core component of the Binder mechanism, which is responsible for the underlying implementation of inter-process communication. Each process has a Binder driver instance to manage the Binder objects in the process.
2. Binder object: Each Binder object in a process has a unique identifier, called a Binder reference. A Binder object can be a server or a client. The server provides services, and the client communicates with the server through the Binder reference.
3. Binder communication process: When the client needs to communicate with the server, it sends a request to the Binder driver through the Binder reference. The Binder driver finds the corresponding server Binder object based on the Binder reference and forwards the request to the server.
4. Inter-process data transmission: The Binder mechanism supports inter-process data transmission. When a client sends a request, it can attach data. After receiving the request, the server can read the data in the request and return the response data to the client.
5. Asynchronous communication: The Binder mechanism supports asynchronous communication. The client can send requests asynchronously without waiting for the server's response. After processing the request, the server can send a response to the client through a callback.

The Binder communication process is as follows:

1. Create a Binder object: In the server process, you first need to create an object that inherits from the Binder class, which is used to provide services.
2. Register the Binder object: The server process registers the Binder object with the system's Binder driver so that the client process can communicate with the server process through the Binder driver.
3. Obtaining a Binder object reference: The client process obtains a Binder object reference from the server process through the Binder driver.
4. Calling remote methods: The client process calls the method of the server process through the Binder object reference to achieve communication between processes.
5. Parameter passing and return value: The client process can pass data to the server process through parameter passing, and the server process can return the result to the client process through return value.
6. Destroy the Binder object: When the communication is over, the client process can release the Binder object reference, and the server process can deregister the Binder object.

During Binder communication, data transmission is achieved through serialization and deserialization. The client process serializes the data and passes it to the server process. The server process deserializes the data after receiving it. This ensures the correct transmission of data between different processes.

picture

Binder communication is an efficient and reliable inter-process communication mechanism. It is widely used in various scenarios in the Android system, such as cross-process calls and remote services.

Summarize

Android uses Binder as the IPC inter-process communication mechanism for the following reasons:

1. Efficiency: Binder is a lightweight IPC mechanism based on the kernel. Compared with other IPC mechanisms (such as Socket, pipe, etc.), Binder has higher performance and lower resource consumption. It achieves efficient inter-process communication through shared memory and zero-copy technology.
2. Security: Binder provides a secure IPC mechanism to ensure that data transmission between different processes is trustworthy. It prevents malicious processes from harming the system through permission verification and sandbox mechanisms.
3. Support cross-process calls: Binder supports cross-process calls (Remote Procedure Call, RPC), allowing applications to call remote object methods between different processes. This cross-process calling capability facilitates Android's componentized architecture, allowing different applications to interact and share resources.
4. Support multi-threaded concurrency: Binder supports multi-threaded concurrent access, which allows multiple threads to access the same remote object at the same time. This is very important for Android applications because Android applications are usually multi-threaded.