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IDProjectCategoryView StatusDate SubmittedLast Update
0002893OCamlOCaml generalpublic2004-07-03 03:272007-12-06 15:34
Reporteradministrator 
Assigned To 
PrioritynormalSeverityminorReproducibilityalways
StatusclosedResolutionfixed 
PlatformOSOS Version
Product Version 
Target VersionFixed in Version3.08.0 
Summary0002893: SEGV when using Gc.finalise
DescriptionFull_Name: Mike Furr
Version: 3.07 & cvs-3.08
OS: OS X & linux
Submission from: pcp01781388pcs.howard01.md.comcast.net (68.32.48.24)


The program below segfaults on my mac and my linux box when compiled with
either the native code or byte code compilers. I have observed this behavior in

both 3.07 and the branch tagged release308 in CVS(7/2/04). This particular
version of the program segv's on 3.08, but not 3.07, but I can supply a larger
version which kills 3.07 if it would help(I tried to create the smallest test
case
to trigger it).
I'm running Debian/unstable on my i386 linux box and OS X 10.2 on my mac.
Note, while trying to slim down the program to submit, I got different
backtraces from gdb along the way...so it seems that the stack is being smashed
somewhere and thus I don't know how useful a bt would be, but here is one
just in case:
furrm@Kamino:~/devel/cache$ gdb ./test
[...]
This GDB was configured as "powerpc-apple-macos10".
Reading symbols for shared libraries .. done
(gdb) run
Starting program: /Users/furrm/devel/cache/test
[Switching to process 19826 thread 0xb03]
Reading symbols for shared libraries .. done

Program received signal EXC_BAD_ACCESS, Could not access memory.
0x00022608 in caml_fl_allocate ()
(gdb) bt
#0 0x00022608 in caml_fl_allocate ()
#1 0x00015f70 in caml_alloc_shr ()
#2 0x0001f150 in caml_weak_create ()
0000003 0x00013234 in caml_c_call ()
Cannot access memory at address 0x181


Here is the program:

module H =
struct
  type t = string
  let equal t1 t2 = (String.compare t1 t2 = 0)
  let hash = Hashtbl.hash
end

module Cache = Weak.Make (H)

let final elt = ()

let cache = Cache.create 2047;;

let _ =
    for i = 0 to 100000 do
      let v = String.create ((i mod 10)+1) in
    Gc.finalise final v;
    Cache.add cache v
    done

Let me know if I can provide any other information.

TagsNo tags attached.
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-  Notes
(0003080)
administrator (administrator)
2004-07-03 12:04

 > Full_Name: Mike Furr
> Version: 3.07 & cvs-3.08

> The program below segfaults on my mac and my linux box when compiled with
> either the native code or byte code compilers. I have observed this behavior
in
> both 3.07 and the branch tagged release308 in CVS(7/2/04). This particular
> version of the program segv's on 3.08, but not 3.07, but I can supply a
larger
> version which kills 3.07 if it would help(I tried to create the smallest test
> case to trigger it).

Thanks for finding this bug. It is now fixed in the release308 branch.
However, I'm still interested in a reproduction case for 3.07, since it seems
to be a different bug.

-- Damien
(0003081)
administrator (administrator)
2004-07-03 12:54

 On Sat, 3 Jul 2004, Damien Doligez wrote:
> Thanks for finding this bug. It is now fixed in the release308 branch.
> However, I'm still interested in a reproduction case for 3.07, since it seems
> to be a different bug.
Attached. This program crashes on my mac with 3.07 and uses all available
memory(1G) on my linux box. It appears to run correctly with 3.08alpha
after your recent changes.

-mike

----------------

open Printf

type elt = {
  id : int;
  mutable life : int;
  data : string;
}
    
let uniq = ref 0;;

module H =
struct
  type t = elt
  let equal t1 t2 = t1.id = t2.id
  let hash t = Hashtbl.hash t.id
end

module Cache = Weak.Make (H)

let keeparound = Hashtbl.create 127;;

let cache = Cache.create 2047;;

let mk num =
  incr uniq;
  {id = !uniq;
   life = 1;
   data = String.create ((num mod 10)+1);
  }

let alarm () = Hashtbl.clear keeparound

let rec final elt =
  if elt.life > 0 then
    begin
      (* Gc.finalise final elt *)
      elt.life <- elt.life - 1;
      Hashtbl.add keeparound elt elt.id;
    end
  else begin
    fprintf stderr "freeing %d\n" elt.id;
    flush stderr;
  end
      

let _ =
  ignore(Gc.create_alarm alarm);
  let count = ref 0 in
    for i = 0 to 100000 do
      let v = mk i in
    Gc.finalise final v;
    (*Cache.add cache v -- segv's withor without this line *)
    done;
    Gc.full_major();
    Gc.print_stat stdout
----------------
----------------
(0003082)
administrator (administrator)
2004-07-12 15:36

 fixed for 3.08+alpha --DD 2004-07-03
can't reproduce crash on 3.07+2
uses all memory because of reentrancy into Hashtbl.resize

- Issue History
Date Modified Username Field Change
2005-11-18 10:14 administrator New Issue
2007-12-06 15:34 doligez Status acknowledged => closed
2007-12-06 15:34 doligez Resolution unable to reproduce => fixed
2007-12-06 15:34 doligez Fixed in Version => 3.08.0
2007-12-06 15:34 doligez Description Updated

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