Re: libjava testsuite failures (regressions 3.2 -> 3.3)

[Mark Wielaard <mark at klomp dot org>]

Hi,

On Sat, 2003-01-18 at 04:57, Jeff Sturm wrote:
> Indeed.  What's interesting about this example is that the gij test takes
> over 60 seconds on my x86-linux laptop if compiled with gcj -C, but
> finishes in only 4 seconds if compiled with javac!
> 
> Without looking at the bytecode, I'd guess javac is hoisting the
> SyncTest.class lookup out of the while loop, whereas gcj -C performs no
> optimizations.
> 
> Doing this by hand might be appropriate for the test case, to prevent
> annoying timeouts:

Good observation. The same speedup can be seen by compiling with jikes.
The timeouts disappear with your patch (but see below).

Attached is the jcf-dump output for the run() method as compiled with
gcj -C and jikes. The trick that jikes uses is to create a new static
field to store the result of the call to SyncTest.class$() which
eventually calls Class.forName(). This field is initialized to null and
then initialized only once.

We could do the same kind of thing, but this does not seem to be the
root cause of this problem. The SyncTest as compiled by gcj -C seems to
have a real deadlock some of the times (this does never happen with gij
3.2 it seems, which is also much faster on this test then gij 3.3).

Also attached is the stackdump of all threads when SyncTest is
deadlocked. All threads are in the garbage collector and I believe this
is the same issue that I sometimes had when running Eclipse with gij.
One of the threads calls dl_iterate_phdr and Hans Boehm explained to me
that method acquires a lock which is a problem when that thread is
stopped by the garbage collector as seems to be the case here. I believe
that he had a fix for this.

Cheers,

Mark
SyncTest.run() as compiled by gcj -C:

Method name:"run" public Signature: 34=()void
Attribute "Code", length:94, max_stack:2, max_locals:5, code_length:50
  0: iconst_0
  1: istore_1
  2: iload_1
  3: ldc #35=<Integer 1000000>
  5: if_icmpge 49
  8: ldc #36=<String "SyncTest">
 10: invokestatic #38=<Method SyncTest.class$ (java.lang.String)java.lang.Class> 13: astore_2
 14: aload_2
 15: monitorenter
 16: getstatic #40=<Field SyncTest.counter int>
 19: iconst_1
 20: iadd
 21: putstatic #40=<Field SyncTest.counter int>
 24: jsr 38
 27: goto 43
 30: astore 4
 32: jsr 38
 35: aload 4
 37: athrow
 38: astore_3
 39: aload_2
 40: monitorexit
 41: ret 3
 43: iinc 1 1
 46: goto 2
 49: return
Exceptions (count: 1):
  start: 16, end: 24, handler: 30, type: 0 /* finally */
Attribute "LineNumberTable", length:18, count: 4
  line: 6 at pc: 0
  line: 6 at pc: 2
  line: 8 at pc: 16
  line: 6 at pc: 43

SyncTest.run() as compiled by jikes:

Method name:"run" public Signature: 13=()void
Attribute "Code", length:116, max_stack:2, max_locals:4, code_length:52
  0: iconst_0
  1: istore_1
  2: goto 45
  5: goto 11
  8: aload_2
  9: monitorexit
 10: athrow
 11: getstatic #17=<Field SyncTest.class$SyncTest java.lang.Class>
 14: dup
 15: ifnonnull 29
 18: pop
 19: ldc #18=<String "[LSyncTest;">
 21: iconst_0
 22: invokestatic #23=<Method SyncTest.class$ (java.lang.String,boolean)java.lang.Class>
 25: dup
 26: putstatic #17=<Field SyncTest.class$SyncTest java.lang.Class>
 29: dup
 30: astore_2
 31: monitorenter
 32: getstatic #25=<Field SyncTest.counter int>
 35: iconst_1
 36: iadd
 37: putstatic #25=<Field SyncTest.counter int>
 40: aload_2
 41: monitorexit
 42: iinc 1 1
 45: iload_1
 46: ldc #26=<Integer 1000000>
 48: if_icmplt 5
 51: return
Exceptions (count: 2):
  start: 8, end: 10, handler: 8, type: 0 /* finally */
  start: 32, end: 42, handler: 8, type: 0 /* finally */
Attribute "LineNumberTable", length:30, count: 7
  line: 6 at pc: 0
  line: 6 at pc: 0
  line: 7 at pc: 5
  line: 8 at pc: 32
  line: 6 at pc: 42
  line: 6 at pc: 45
  line: 10 at pc: 51

Attachment: stack
Description: Text document