Signature SIGNAL Structure Signal Basis HashArray SingleAssignment

Although the Posix structure in the Standard Basis Library provides functions which send signals to a process there is no standard method of handling signals. The Signal structure has been added to Poly/ML to allow signals to be blocked or handled.

signature SIGNAL: sig datatype sig_handle = SIG_DFL | SIG_IGN | SIG_HANDLE of int -> unit val signal: int * sig_handle -> sig_handle end structure Signal: SIGNAL datatype sig_handle = SIG_DFL | SIG_IGN | SIG_HANDLE of int -> unit

val signal : int * sig_handle -> sig_handle

The Signal.signal function takes as its arguments a signal number and an action and returns the previous action. The action may be SIG_DFL, indicating the default action, SIG_IGN, indicating that the signal should be ignored (blocked) or SIG_HANDLE, which allows a handler function to be installed.

Signals are represented as integers using the normal Unix signal numbering. In the Unix implementations of Poly/ML the type Posix.Signal.signal is the same as int so the constants from Posix.Signal can be used as arguments to Signal.signal.

The default action depends on the signal. For some signals it is to ignore the signal, for others the process is killed. See the signal man page in Unix for a list of the default actions.

A handler function installed using SIG_HANDLE is run as a separate thread some time after a signal arrives.

Some signals are used internally by Poly/ML. In particular SIGVTALRM is used by the profiling mechanism.

The Signal structure is provided in the Windows implementation but only the console interrupt signal (2) has effect.