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Signature OS_PROCESS (basis)

Operating system processes. 

structure Process : OS_PROCESS (basis)

signature OS_PROCESS =
  sig
    type status
    val success   : status
    val failure   : status
    val isSuccess : status -> bool
    val system    : string -> status
    val atExit    : (unit -> unit) -> unit
    val exit      : status -> 'a
    val terminate : status -> 'a
    val getEnv    : string -> string option
    val sleep     : Time.time -> unit
  end
[type status]
The status type represents various termination conditions for processes. On POSIX-based systems, status will typically be an integral value.

[success]
The unique status value that signifies successful termination of a process.

[failure]
A status value that signifies an error during execution of a process. Note that, in contrast to the success value, there may be other failure values.

[isSuccess sts]
returns true if the status denotes success.

[system cmd]
passes the command string cmd to the operating system's default shell to execute. It returns the termination status resulting from executing the command. It raises SysErr if the command cannot be executed. Note that, although this function is independent of the operating system, the interpretation of the string cmd depends very much on the underlying operating system and shell. On Unix systems, the default shell is "/bin/sh"; on Microsoft Windows systems, the default shell is the Microsoft Windows shell; on MacOS systems, the command is compiled and executed as an Apple script.

[atExit f]
registers an action f to be executed when the current SML program calls exit. Actions will be executed in the reverse order of registration. Exceptions raised when f is invoked that escape it are trapped and ignored. Calls in f to atExit are ignored. Calls to exit do not return, but should cause the remainder of the functions registered with atExit to be executed. Calls to terminate (or similar functions such as Posix.Process.exit) will terminate the process immediately.

[exit st]
executes all actions registered with atExit, flushes and closes all I/O streams opened using the Library, then terminates the SML process with termination status st. Implementation note: 
    If the argument to exit comes from system or some other function
    (such as Unix.reap) returning a status value, then the
    implementation should attempt to preserve the meaning of the exit
    code from the subprocess.  For example, on a POSIX system, if
    Posix.Process.fromStatus st yields Posix.Process.W_EXITSTATUS v,
    then v should be passed to Posix.Process.exit after all necessary
    cleanup is done.

    If st does not connote an exit value, exit should act as though
    called with failure.  For example, on a POSIX system, this would
    occur if Posix.Process.fromStatus st is Posix.Process.W_SIGNALED
    or Posix.Process.W_STOPPED.

[terminate st]
terminates the SML process with termination status st, without executing the actions registered with atExit or flushing open I/O streams.

[getEnv s]
returns the value of the environment variable s, if defined. Otherwise, it returns NONE. An environment is associated with each SML process, modeled as a list of pairs of strings, corresponding to name-value pairs. (The way the environment is established depends on the host operating system.) The getEnv function scans the environment for a pair whose first component equals s. If successful, it returns the second component.

[sleep t]
suspends the calling process for the time specified by t. If t is zero or negative, then the calling process does not sleep, but returns immediately. No exception is raised.

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