UNIXUNIX signals

UNIX signals

This topic examines UNIX signals in relationship to the D3 virtual machine.

The discussion is intended for experienced UNIX programmers to interface UNIX applications with D3 or to use UNIX process synchronization in a purely D3 environment.

For performance reasons, UNIX signals are not used in regular D3 activity. They are used solely to handle exceptions. Diverting signal usage for an application would remove nonessential facilities, such as sending messages or logging off a process. This does not mean that signals can be used freely, though. The D3 monitor provides a system call to process regular D3 signals inside a customized signal handler, thus combining system and application signal handling.

  1. Signal usage
    D3 uses only UNIX System V.3 signals, which are common to more recent UNIX versions. Those systems that are not UNIX System V.3 signals are left to their default signal handler (such as, SIG_IGN) as set by the system.
  2. Signal description
    This table lists the signals currently used by D3.
  3. D3 signal system call
    The D3 monitor provides a system call to inform the D3 Virtual Environment of an incoming signal. This c function is called by the default signal system handlers, but also can be called by an application signal handler.
  4. Synchronizing two D3 processes
    On most conventional D3 implementations, synchronizing two D3 processes is done either through polling for the existence of a file or, more preferably, by using a FlashBASIC lock instruction. On most implementations, however, the FlashBASIC lock instruction itself involves, internally, a polling, thus causing the waiting process to consume CPU resources. By using signals, it is possible to have a process waiting for a signal to occur (a Break, log off or a signal generated by another process, possibly a UNIX process or a D3 process from another D3 virtual machine) without any CPU consumption.

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