Implementing inter-process communication in Linux using signal handling

Inter-Process Communication (IPC for short) is a mechanism for information exchange and data transmission between different processes. Linux provides a variety of IPC methods, one of the common methods is to use signal processing to achieve inter-process communication. The following will introduce in detail how to use signal processing for inter-process communication in Linux, including the basic concept of signals, the mechanism and implementation of signal processing.

1. Basic concepts of signals

1. Signal: A signal is a software interrupt used to notify the process that a certain event has occurred. When an event occurs, the operating system sends a signal to the process, and the process can choose to handle or ignore the signal.

2. Signal number: Each signal has a unique digital number. In Linux, signal numbers are represented by macro definitions. For example, SIGINT represents a terminal interrupt signal.

3. Signal processing function: When a process receives a signal, it can choose to process the signal by registering a signal processing function. The signal processing function is a user-defined function that is used to specify the operations that need to be performed when a signal is received.

2. Signal processing mechanism

1. Signal sending: Signals can be sent by the kernel, other processes, or the current process itself. Common ways of sending signals include keyboard input, operating system events, software errors, etc.

2. Signal delivery: When a process receives a signal, it can choose to ignore the signal, perform a default operation, or call a registered signal processing function. If you choose to call a signal handling function, the process will perform the specified operations in the signal handling function.

3. Signal processing process: When a signal is sent to a process, the operating system will first check how the process handles the signal. If the process has registered a signal handling function, the function is called to handle the signal; if the process does not register a signal handling function, the corresponding operation will be performed according to the default operation of the signal.

4. Interrupt the current operation: In most cases, the process that receives the signal will interrupt the current operation and execute the signal processing function instead. This is because the arrival of a signal often indicates that an important event has occurred and needs to be processed with priority.

5. After the signal processing is completed: When the signal processing function is executed, the process will return to the original state and continue execution.

3. Use signal processing to implement inter-process communication

1. Sending signals: A process can send information to other processes by sending signals. Use the kill function (or related system call function) to send a specified signal to a specified process, such as kill(pid, signal).

2. Receive signals: A process can receive and process signals by registering a signal processing function. Use the signal function (or related system call function) to register a signal processing function, such as signal(signal, sig_handler).

3. Signal processing function: The signal processing function is a user-defined function that is used to specify the operations that need to be performed when a signal is received. Different signal processing functions can be written according to specific needs, such as executing corresponding processing logic after capturing a specific signal.

4. Signal synchronization: In order to ensure the reliability and synchronization of inter-process communication, signals can be used for process synchronization. For example, a process waits for another process to complete a certain task and then sends a signal to itself, thereby triggering subsequent operations.

4. Precautions for signal processing

When using signal processing for inter-process communication, you need to pay attention to the following issues:

1. Signal reliability: The sending and receiving of signals are asynchronous, that is, the sender cannot guarantee that the signal will be received by the receiver. Therefore, when designing a signal processing mechanism, the reliability of the signal and the possibility of loss need to be considered.

2. Blocking of signals: A process can choose to block certain signals to avoid receiving these signals during critical operations. The signal mask can be set by calling the sigprocmask function to determine which signals can be delivered to the process.

3. Signal queuing: For some signals, when the signal arrives, if the signal has been blocked, the system will queue it until the signal is unblocked before it is delivered to the process.

4. Signal concurrency: Multiple signals may arrive at a process at the same time. Therefore, when processing signals, you need to consider the issues of concurrent processing and race conditions, and design the signal processing function reasonably.

By using signal handling mechanisms, communication and synchronization between processes can be achieved. The signal processing mechanism is a simple and effective IPC method in Linux, which can be used to send messages, notify events, process synchronization, etc. However, it is necessary to pay attention to issues such as signal reliability, blocking and queuing, and concurrent processing to ensure the correctness and stability of inter-process communication. Reasonable use of signal processing can improve the flexibility and responsiveness of the program, thereby achieving more efficient and reliable inter-process communication.