Asynchronous signals

Asynchronous signals

Asynchronous signals are generated outside the application (for example, SIGALRM, SIGINT, and SIGTERM). InterSystems IRIS handles all asynchronous signals that would terminate the process.

Asynchronous signals may be caught by any thread that has not blocked the signal. The system chooses which thread to use. Any signal whose default action is to cause the process to exit must be handled, with at least one thread eligible to receive it, or else it must be specifically ignored.

The application must establish a signal handler for those signals it wants to handle, and must start a thread that does not block those signals. That thread will then be the only one eligible to receive the signal and handle it. Both the handler and the eligible thread must exist before the application makes its first call to IrisStart. On the first call to IrisStart, the following actions are performed for all asynchronous signals that would terminate the process:

• InterSystems IRIS looks for a handler for these signals. If a handler is found, InterSystems IRIS leaves it in place. Otherwise, it sets the signal to SIG_IGN (ignore the signal).

• InterSystems IRIS blocks all of these signals for connected threads, whether or not a signal has a handler. Thus, if there is a handler, only a thread that is not connected to InterSystems IRIS can catch the signal.

The following signals are affected by this process: