gc and pf pseudocode

内存受限系统软件开发一书的代码。（虽不及Gang of Four的模式掷地有声

Memo #814 (2340)
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Date: Tue, 11 Jan 2000 15:25:26 +1300 (NZDT)
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From: James Noble <[e-mail]>
To: [e-mail]
Subject: Code Example: GC
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GC CODE EXAMPLE --- Pass #1

the text below is cut from the chapter.

Q: do you have the test cases for the reference-counting example?

After thinking a bit, those tests should all apply to the GC version.

[this example is not even pseudo code,  needs to be completed]

[show how to add a simple, stack-based mark-sweep GC to the example from the reference counting pattern.]

class GarbageCollectedThing: public ReferenceCountedThing {
                                      // should this just be thing??
public:
    void mark();
              void sweep();
protected:
    bool markBit;
};

void setupPhase() {
	//for all objects, set markBit to FALSE
   //should be done on creation
}

void markPhase() {
	for (r = root; r < lastRoot; r++) {
		r.mark(); };
}

void mark() {
	if (markBit) return;
	markBit = TRUE;
	for (r = all_my_fields; r < lastField; r++) {
		r.mark(); };
	}

void sweepPhase() {
	for (p = first_object; p < lastObject; p++) {
		if (p.markBit) {
			p.markBit = FALSE;
		} else { 
			delete p;;
		}
}

Note that this example can be extended to recompute reference counts -
the mark phase should just increment an integer instead of setting a
bit.  [illustrate this in the final example]




Memo #815 (1777)
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Date: Tue, 11 Jan 2000 15:27:30 +1300 (NZDT)
Message-Id: <[e-mail]>
From: James Noble <[e-mail]>
To: [e-mail]
Subject: Code Example: PF
X-UIDL: 213463a009b40940688bd331330c55d4

text pulled from Partial Failure in the Arch chapter.


[example is in pseudo code, needs to be translated into real code]
Font findFont(String fontDescription) {

	If fontCache.includes(fontDescription)
         return fontCache.get(fontDescription);

	Font f;  // stores possible fonts

	Try { // create a font
		f = new Font(fontDescription);
	}
	catch (OutOfMemory oom) {
		// on this exception, f will be nill
		// don't rethrow the exception yet
	}

	if (f != null) {return f;}

	if ((f = fontCache.findmatching(fontDescripton)) != nil) {
		return f; }
	if (cachedSystemFont != null) {return cachedSystemFont;}
	
	throw OutOfMemory(self);
}