Receive software termination signal

As the name implies, there is a single Global namespace system-wide. The CreateEvent function is used to surprise!

It can create either a named or unnamed event. By creating a named event, the OS enforces that only a single instance of the object exists in that namespace at any one time and that all processes referring to that event will receive a handle to the same instance, creating a form of interprocess communication.

Thus if the Local namespace is used, then the event object is shared across all processes that refer to it in that client session. Likewise if it is created in the Global namespace, it is shared across all processes that refer to it on the entire system.

There are two reset mechanisms used by event objects: AutoReset and ManualReset. An AutoReset event will automatically be reset to a non-signaled state as soon as single waiting thread is released.

A ManualReset event requires a call to ResetEvent in order to be returned to a non-signaled state. Lastly, an event can be set to either the signaled or non-signaled state when it is initially created. By combining the concept of checking for a signaled event to determine when to shutdown and using a named event object, it is possible to signal one process to shutdown via another process.

As with an alarm signal, the actual return may occur at a time later than requested because of other system activity. Although sleep can be implemented with the alarm function Section If alarm is used, there can be interactions between the two functions. This function is a modification of Figure This code doesn't use any form of nonlocal branching as in Figure The nanosleep function is similar to the sleep function, but provides nanosecond-level granularity. This function suspends the calling process until either the requested time has elapsed or the function is interrupted by a signal.

Some applications require precision with how long they sleep, and a relative sleep time can lead to sleeping longer than desired. Using an absolute time improves the precision, even though a time-sharing process scheduler makes no guarantee that our task will execute immediately after our sleep time has ended. With SUSv4, the queued signal functionality has moved from the real-time extensions to the base specification. These extensions allow applications to pass more information along with the delivery Section This information is embedded in a siginfo structure.

The following program demonstrates the normal sequence of code used when a program handles job control. This section discusses how to map between signal numbers and names. Some systems provide the array:. The array index is the signal number, giving a pointer to the character string name of the signal. To print the signal's character string in a portable manner, use the psignal function:. The string msg which normally includes the name of the program is output to the standard error, followed by a colon and a space, followed by a description of the signal, followed by a newline.

If msg is NULL , then only the description is written to the standard error. This function is similar to perror Section 1. If you have a siginfo structure from an alternative sigaction signal handler, you can print the signal information with the psiginfo function.

You can use the strsignal function if you only need the string description of the signal. This function is similar to strerror Section 1. Solution : They are integer that cast into an address which means the "pointer to a function that takes an integer argument and returns nothing". Question : What is exactly the window? Shouldn't be the unblocked signals delivered to the process? Not fully understood. Toggle navigation Shichao's Notes. Files and Directories Chapter 5.

System Data Files and Information Chapter 7. Process Environment Chapter 8. Process Control Chapter 9. Process Relationships Chapter Signals Chapter Threads Chapter Thread Control Chapter Daemon Processes Chapter Interprocess Communication Chapter Introduction Chapter 2.

Sockets Introduction Chapter 4. Socket Options Chapter 8. The Internet Address Architecture Chapter 3. Link Layer Chapter 4. TCP Keepalive Chapter Tutorial Chapter 2. Program Structure Chapter 3. Basic Data Types Chapter 4. Composite Types Chapter 5. Functions Chapter 6. Methods Chapter 7. Interfaces Chapter 8. Goroutines and Channels Chapter 9.

Concurrency with Shared Variables Chapter Packages and the Go Tool Chapter Testing Chapter Chapter They all begin with the three characters SIG. It bad for the kernel to include header files meant for user-level applications, so if the applications and the kernel both need the same definitions, the information is placed in a kernel header file that is then included by the user-level header file. The kill function uses the signal number of 0 for a special case. Numerous conditions can generate a signal: The terminal-generated signals occur when users press certain terminal keys.

Hardware exceptions generate signals. For example, divide by 0 and invalid memory reference. These conditions are usually detected by the hardware, and the kernel is notified. The kernel then generates the appropriate signal for the process that was running at the time the condition occurred. The kill 1 command allows us to send signals to other processes.

This program is just an interface to the kill function. This command is often used to terminate a runaway background process. Software conditions can generate signals when a process should be notified of various events. If we ignore some of the signals that are generated by a hardware exception such as illegal memory reference or divide by 0 , the behavior of the process is undefined. Catch the signal. To do this, we tell the kernel to call a function of ours whenever the signal occurs.

In our function, we can do whatever we want to handle the condition. If the process has created temporary files, we may want to write a signal-catching function for the SIGTERM signal the termination signal that is the default signal sent by the kill command to clean up the temporary files.

Let the default action apply. Every signal has a default action. The default action for most signals is to terminate the process. The process terminates abnormally. This signal is also generated when an interval timer set by the setitimer 2 function expires. Implementations usually generate this signal on certain types of memory faults. It is not meant for general use.

Not all platforms support this signal. The name is derived from "floating-point exception" Program Error Signals. The flag tells the terminal driver to ignore all modem status lines. The session leader that receives this signal may be in the background Figure 9. This differs from the normal terminal-generated signals interrupt, quit, and suspend , which are always delivered to the foreground process group.

This signal is also generated if the session leader terminates. In this case, the signal is sent to each process in the foreground process group. This signal is commonly used to notify daemon processes Chapter 13 to reread their configuration files. The reason SIGHUP is chosen for this task is that a daemon should not have a controlling terminal and would normally never receive this signal. This signal is sent to all processes in the foreground process group Figure 9. This signal normally causes status information on processes in the foreground process group to be displayed on the terminal.

It provides the system administrator with a sure way to kill any process. It can be generated when a specific event occurs on a pollable device. This signal is generated when a profiling interval timer set by the setitimer 2 function expires.

If power fails, the UPS takes over and the software can usually be notified. Nothing needs to be done at this point, as the system continues running on battery power. But if the battery gets low, the software is usually notified again; at this point, it behooves the system to shut everything down.

The process that is notified of the low-battery condition sends the SIGPWR signal to the init process, and init handles the system shutdown. Solaris 10 and some Linux distributions have entries in the inittab file for this purpose: powerfail and powerwait or powerokwait.

The default on Linux is to terminate the process. On Solaris, the signal is ignored by default. SIGSEGV : indicates that the process has made an invalid memory reference which is usually a sign that the program has a bug, such as dereferencing an uninitialized pointer. The name SEGV stands for "segmentation violation".

It showed up in the earliest versions of Linux, where it was intended to be used for stack faults taken by the math coprocessor. This signal is not generated by the kernel, but remains for backward compatibility. The process executed a machine instruction that the kernel thought was a system call, but the parameter with the instruction that indicates the type of system call was invalid.

SIGTHAW : defined only by Solaris and used to notify processes that need to take special action when the system resumes operation after being suspended. Implementations often use this signal to transfer control to a debugger when a breakpoint instruction is executed. If either of the following case occurs, the signal is not generated; instead, the read operation fails with errno set to EIO : The reading process is ignoring or blocking this signal.

The process group of the reading process is orphaned. If background writes are not allowed, then like the SIGTTIN signal, the signal is not generated if either of the following cases occurs; instead, the read operation fails with errno set to EIO : The writing process is ignoring or blocking this signal The process group of the writing process is orphaned Regardless of whether background writes are allowed, certain terminal operations other than writing , including tcsetattr , tcsendbreak , tcdrain , tcflush , tcflow , and tcsetpgrp can also generate the SIGTTOU signal.

A process can get and set the window size with the ioctl function. If a process changes the window size from its previous value using the ioctl set-window-size command, the kernel generates the SIGWINCH signal for the foreground process group. The default action depends on the operating system. Linux 3. The new signal mask for the process is the union of its current signal mask and the signal set pointed to by set.

That is, set contains the additional signals that we want to block. The new signal mask for the process is the intersection of its current signal mask and the complement of the signal set pointed to by set. Some signals, such as the interrupt signal, indicate that a user has asked the program to do something that is not in the usual flow of control.

There is an easy way to list down all the signals supported by your system. Every signal has a default action associated with it. The default action for a signal is the action that a script or program performs when it receives a signal.

Dump core. This creates a file called core containing the memory image of the process when it received the signal. There are several methods of delivering signals to a program or script. Here signal is either the number or name of the signal to deliver and pid is the process ID that the signal should be sent to.

The above command sends the HUP or hang-up signal to the program that is running with process ID This may not always be desirable. For instance, you may end up leaving a bunch of temporary files that won't get cleaned up.

Here command can be any valid Unix command, or even a user-defined function, and signal can be a list of any number of signals you want to trap.