89 lines
3.0 KiB
Plaintext
89 lines
3.0 KiB
Plaintext
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DEFINITION MODULE Program;
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(*
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Sub-program loading and execution
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Derived from the Lilith Modula-2 system developed by the
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group of Prof. N. Wirth at ETH Zurich, Switzerland.
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Under Modula-2/86, programs can be divided into
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sub-programs (we call them 'programs') which are
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loaded upon request.
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These programs are executed like procedures:
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- they have only one entry-point (body of
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program's main module).
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- after termination, their data do not exist any
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longer. In the case of programs the code also
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disappears and will be reloaded from disk upon
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the next activation.
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- programs may themselves activate other programs.
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*)
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FROM System IMPORT Status;
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EXPORT QUALIFIED Call, GetErrorInfo;
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PROCEDURE GetErrorInfo (VAR msg: ARRAY OF CHAR);
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(*- Obtain more information about a load error.
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out: msg a string related to the last error.
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After Call (below) has returned a Status value of
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'modulenotfound' and 'incompatiblemodules', GetErrorInfo
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will return the name of the offending module. (length is up
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to 24 characters). It returns an empty string in all other
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cases.
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*)
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PROCEDURE Call (programName: ARRAY OF CHAR; shared: BOOLEAN;
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VAR st: Status);
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(*- Load and execute a (sub) program.
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in: programName file specification for the program,
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shared whether to share resources,
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out: st terminating status of the subprogram.
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The file whose name is given in 'programName' is opened
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loaded, and started. There is no default device or file type:
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these must be supplied by the caller. The file must contain a
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linked, relocatable program.
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The load address is defined by the default allocation schema,
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in which programs are loaded on top of stack and a new stack is
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created for execution of the new program.
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If 'shared' = TRUE then all sharable resources allocated by
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the called program are owned by the calling program (or
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possibly the caller of the caller...). Shared resources are
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not released upon termination of the new program.
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Upon termination of the program, its memory is freed and the
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old stack is established. All the resources used by a
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terminating program are released, if they are not shared and
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if they have not been released explicitly by the program
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(files, heap, etc).
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Any value of 'st' other than 'normal' indicates an abnormal
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termination of the subprogram. In some cases GetErrorInfo (above)
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will provide additional details.
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- Cautions -
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In case of abnormal termination, Call does NOT print any kind
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of error message.
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Do not assign a procedure in the current program to a procedure
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variable which could still exist after the current program
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terminates (for example, a variable in a shared resource or in
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the calling program). When the current program terminates,
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all procedures in it must be considered to cease to exist.
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The loader in this module is not reentrant. This means that
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interrupt processes must not load overlays!
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*)
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END Program.
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