Signal processing techniques in C++

C is a popular programming language that is powerful and flexible, suitable for a variety of application development. When developing applications in C, you often need to handle various signals. This article will introduce signal processing techniques in C to help developers better master this aspect.

1. Basic concepts of signal processing

A signal is a software interrupt used to notify the application of internal or external events. When a specific event occurs, the operating system sends a signal to the application, which the application can choose to ignore or respond to. In C, signals can be processed through signal handling functions. When an application receives a signal, it calls the signal handling function corresponding to the received signal.

2. Registration of signal processing functions

The signal processing functions in C need to be registered in the application so that they can be called when receiving a specific signal. Registration can be done using the "signal" function in the C standard library. The following is an example:

#include <signal.h>
#include <iostream>

void signal_handler(int signum){
    std::cout << "Received signal: " << signum << std::endl;
}

int main() {
    signal(SIGINT, signal_handler);
    while (true) {}
    return 0;
}

In the above example, we defined a function named "signal_handler", which will output the signal number when a signal is received. Use the "signal" function to associate the SIGINT signal with the "signal_handler" function. "while (true)" is used to wait for the reception of the signal.

3. Classification of signals

In C, signals can be divided into two types: standard signals and real-time signals.

Standard signals are sent by the operating system to notify applications of events that have occurred. Standard signals in C include: SIGABRT, SIGALRM, SIGFPE, SIGHUP, SIGILL, SIGINT, SIGKILL, SIGPIPE, SIGQUIT, SIGSEGV, SIGTERM and SIGUSR1/SIGUSR2. These signals can be processed through signal processing functions.

Real-time signals are sent by applications to notify other applications or threads of events. Real-time signals in C include: SIGRTMIN/SIGRTMAX. Unlike standard signals, real-time signals are reliable and deterministic.

4. Signal usage skills

1. Priority of signal response

The signal response in C is determined according to priority. Different signals have different priorities. You can control the signal response by modifying the priority of the signal processing function. The priority is identified using the "sa_flags" field, and the priority order is: SA_SHIRQ, SA_RESTART, SA_NODEFER, SA_ONSTACK, SA_NOCLDSTOP, SA_NOCLDWAIT, SA_SIGINFO and SA_RESETHAND.

2. Signal blocking

When an application receives a signal, the operating system marks the signal as pending. If the application receives the same signal again at this time, the operating system will discard the signal and the signal processing function will not be triggered. This situation is called signal blocking. In C, you can use the "sigprocmask" function to block signals, as shown below:

#include <signal.h>

int main() {
    sigset_t mask;
    sigemptyset(&mask);
    sigaddset(&mask, SIGINT);
    sigprocmask(SIG_BLOCK, &mask, NULL);
    while (true) {}
    return 0;
}

In the above example, we use the "sigprocmask" function to block the SIGINT signal. When executing the "while (true)" statement, the signal will be blocked and the signal processing function will not be triggered.

3. Signal capture

Signal capture in C can be achieved by installing a signal processor. You can use the "sigaction" function to install a signal handler and bind a specific signal handler to a specific signal. The following is an example:

#include <signal.h>
#include <iostream>

void signal_handler(int signum){
    std::cout << "Received signal: " << signum << std::endl;
}

int main() {
    struct sigaction act;
    sigemptyset(&act.sa_mask);
    act.sa_flags = 0;
    act.sa_handler = signal_handler;
    sigaction(SIGINT, &act, NULL);
    while (true) {}
    return 0;
}

In the above example, we use the "sigaction" function to bind the SIGINT signal with the "signal_handler" function. When the SIGINT signal is received, the "signal_handler" function will be called to output the signal number.

4. Summary

This article introduces signal processing techniques in C, including registration of signal processing functions, signal classification, signal response priority, signal blocking and signal capture. Understanding these techniques can help developers better grasp the basic concepts and principles of signal processing and improve the reliability and stability of applications.

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