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51 lines
2.1 KiB
Plaintext
51 lines
2.1 KiB
Plaintext
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I just started implementing Classes and objects creation when I realized
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Harbour is not managing static variables yet (Harbour recognizes them but
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does not generate the proper pcode for them).
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So I would like to make an introduction to static variables management as
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it is a sophisticated system that Harbour is going to implement.
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It is something publically known that Clipper static variables are
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located at the bottom of the data segment. This has caused all kinds of
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troubles. This is why when I designed Five I did it in a way that could not
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cause any trouble in the future.
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In Harbour all static variables (and I mean on all PRGs) are stored in
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just one Harbour array (a Clipper language array), this guarantees that we
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may have as many static variables as desired without limits (just limited
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by the available memory). This aStatics array is not visible from the
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application (PRG level).
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Basically what happens when a function is called and that function uses
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static variables, is that the stack sets a pointer to that array section
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where our statics are, so from that moment on, accessing a static1, static2,
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... is accessing some elements on that array:
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static1 = statics[ statics_base_for_this_function + 1 ]
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...
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staticn = statics[ statics_base_for_this_function + n ]
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In order to implement this we just use two new pcode opcodes: _STATICS,
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_SFRAME. _STATICS makes the global statics array grow enough to hold our new
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defined statics:
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_STATICS <n> --> ASize( aStatics, Len( aStatics ) + <n> )
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_SFRAME --> tell the stack from what location into aStatics are ours.
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_STATICS is just called once for an entire PRG from an init function
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named _INITSTATICS (STATICS$ and SINIT in Clipper). That function stores in
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a tricky place (its own function pointer in the symbol table!) our statics
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base, and later on _SFRAME simply takes it from there and sets it in the
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stack. That _INITSTATICS function will perform whatever initialization our
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global statics may have defined in that PRG).
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You are going to see the code for all these. I just wanted to provide a
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clear idea about how Harbour does its magic :-)
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Antonio
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