3.5 Use of Signals

To detect work arriving from other components, the HLLAPI library makes use of the SIGUSR1, SIGUSR2, and SIGALRM signals. Applications may require these signals for other purposes, so the library daisy-chains to any existing signal catchers; the first verb issued by the application initializes the library's signal catchers.

When these signals arrive, they may indicate work, or items may have been generated for some other reason. The library's signal catchers process the signals and then call the previous signal catchers to allow the signals to be used for other purposes.

The following restrictions apply to SIGUSR1 , SIGUSR2, and SIGALRM usage:

• Applications must not permanently disable these signals. sighold/sigrelse can be used to protect a critical region of code, provided that no verbs are issued between sighold and sigrelse.

• Applications that need to add signal catchers should preserve the address of the SNAP-IX signal catchers (returned by the sigset call) and arrange to call these routines from within the new signal catchers.

In addition, you are recommended not to use the POSIX signal mechanism SIGACTN, which may cause problems in SNAP-IX applications.