William Ricker wrote:
> Yes. longjmp was once not only less C code but far far quicker to unwind
> a deep stack than the standard
> return(-1) if rc < 0; # lather rinse repeat
> in old C on old slow hardware without optimized stack instructions. The
> return()'s register swizzling is far cheaper on today's hardware which
> has support for such, so that is less true today. Doing an exception
> throw in OO C++ or Java or even Perl requires MUCH MORE *implicit* work
> as the exception propagates through the call stack checking at each
> frame for potential catches and potential destructors for on-stack
> objects being freed.
As there are somewhat optimized implementations of "return", there are
optimized implementations of exceptions which do not require stack-walking in
order to find the handler code & frame. It is possible to maintain a separate
"handler stack", for example -- numerous other approaches are possible,
depending on the language constraints.
The details vary. CPU support varies. Languages vary. What people are
comfortable using varies.
Perhaps a little code will say something:
foo () {
a = openFile("A");
if ( FAIL = a ) return FAIL;
...use a...
b = openFile("B");
if ( FAIL = b ) { close(a); return FAIL; }
...use a & b...
b = openFile("B");
if ( FAIL = c ) { close(a); close(b); return FAIL; }
...use a & b & c...
...And so on...
close(c); close(b); close(a);
}
bar () {
try {
a = openFile("A");
...use a...
b = openFile("B");
...use a & b...
b = openFile("B");
...use a & b & c...
...And so on...
} finally {
close(c); close(b); close(a);
}
}
baz () {
a = openFile("A");
if ( FAIL = a ) goto a;
...use a...
b = openFile("B");
if ( FAIL = b ) goto b;
...use a & b...
b = openFile("B");
if ( FAIL = c ) goto c;
...use a & b & c...
...And so on...
c: close(c);
b: close(b);
a: close(a); return FAIL;
}
As the saying goes: there's more than one way. Suit yourself.
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