In the C programming language, signals are a mechanism used to notify a process that a specific event has occurred. They are used for handling asynchronous events, such as user inputs (e.g., pressing Ctrl+C), system conditions (e.g., memory access errors), or inter-process communication. When a signal is generated, it interrupts the normal execution flow of a process.
Key Points about Signals:
Signal Types: Each signal has a name and number, such as SIGINT (interrupt from the keyboard), SIGSEGV (segmentation fault), or SIGTERM (termination request).
Signal Handling: Processes can respond to signals in three ways:
Default Action: The operating system takes the default action, such as terminating the process for SIGTERM.
Custom Handlers: The process can define a custom signal handler function to handle the signal in a specific way.
Ignore the Signal: The process can ignore the signal.
Sending Signals: Signals can be sent by the operating system (e.g., due to errors) or by other processes (e.g., using the kill() system call).
Signal Masking: A process can block specific signals temporarily, so they are not handled immediately.
Common Signals:
SIGINT: Sent when the user presses Ctrl+C to interrupt the program.
SIGTERM: Request for the process to terminate.
SIGSEGV: Occurs when the process attempts to access invalid memory (segmentation fault).
SIGKILL: Forces immediate termination of a process (cannot be caught or ignored).
Signal handling allows programs to manage exceptions, errors, and user interrupts efficiently.