Jon Harrop wrote:
> Sure. The Java:
>
[cut]
> void run()
> {
> Exception e = new Exception("");
> try
> {
> for (int i=0; i<3; ++i)
> {
> if (foo(i) == 0) throw e;
> }
> }
> catch (Exception e2)
> {
> }
> bar();
> baz();
> }
>
> public static void main(String[] args)
> {
> for (int n=0; n<10; ++n)
> {
> long start = System.currentTimeMillis();
> for (int i=0; i<1000000; ++i)
> (new test()).run();
> System.out.println(System.currentTimeMillis() - start);
> }
> }
> }
this is not a good benchmark, for two reasons:
1) you are allocating a new object at every loop, but we are
benchmarking the loops, not the garbage collector :-); you should use
static methods instead, IMHO;
2) you are allocating a new exception every time; the optimization
described here [1] works only if the exception is pre-allocated.
[1] http://blogs.sun.com/jrose/entry/longjumps_considered_inexpensive
Here is my modified benchmark which tries to address these issues:
public class loop2
{
public static final Exception exc = new Exception("");
static int foo(int n)
{
return n - 1;
}
static void bar()
{
}
static void baz()
{
}
static void run()
{
try
{
for (int i=0; i<3; ++i)
{
if (foo(i) == 0) throw exc;
}
}
catch (Exception e2)
{
}
bar();
baz();
}
public static void main(String[] args)
{
for (int n=0; n<10; ++n)
{
long start = System.currentTimeMillis();
for (int i=0; i<1000000; ++i)
run();
System.out.println(System.currentTimeMillis() - start);
}
}
}
And here are the results:
[EMAIL PROTECTED] tmp $ java loop1
1923
2032
2032
2052
2031
2078
2058
2035
2067
2063
[EMAIL PROTECTED] tmp $ java loop2
9
3
1
1
1
1
1
1
1
1
Trying to interpret the number, I think that after the first iteration
hotspot decided to JIT compile the loop, and since it can inline the
exception it ends up with a completely empty loop which is thrown away.
ciao,
Anto
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