JRuby

FFI::MemoryPointer becomes unwritable

Details

  • Type: Improvement Improvement
  • Status: Open Open
  • Priority: Major Major
  • Resolution: Unresolved
  • Affects Version/s: None
  • Fix Version/s: None
  • Component/s: Extensions, Windows
  • Labels:
    None
  • Environment:
    jruby 1.6.0.dev (ruby 1.8.7 patchlevel 249) (2010-06-30 2d1eff7) (Java HotSpot(TM) Client VM 1.6.0_18) [x86-java]
    screenshot gem v 0.0.4
  • Testcase included:
    yes
  • Number of attachments :
    0

Description

This code:

require 'rubygems'
require "benchmark"
require 'win32/screenshot'
t = "Internet Explorer"
Benchmark.bmbm do |x|
x.report("no file") {50.times {Win32::Screenshot.window(t, 0) {}}}
end

Eventually crashes [1] in jruby, because a MemoryPointer appears to suddenly be unwritable.

It succeeds well with MRI.

Maybe jruby's underlying FFI implementation should do its own memory management, like calling out to malloc and free, to avoid Java's GC (which I assume is the cause [2]).

-r
[1] http://gist.github.com/458719
[2] http://wiki.github.com/ffi/ffi/core-concepts#memory

Activity

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Roger Pack added a comment -

ref: http://github.com/jarmo/win32screenshot/issues/#issue/2

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Roger Pack added a comment - ref: http://github.com/jarmo/win32screenshot/issues/#issue/2
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Roger Pack added a comment -

also reproducible with this: http://gist.github.com/518855

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Roger Pack added a comment - also reproducible with this: http://gist.github.com/518855
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Wayne Meissner added a comment -

I wonder if this isn't a calling convention problem. Basically the callback may not be getting setup as :stdcall ... or it is when it isn't supposed to be.

Try using a FFI::Function (http://ffi.github.com/api/FFI/Function.html) instead of a proc for the callback.
e.g.

Win::EnumWindowCallback = FFI::Function.new(:bool, [ :pointer, :long ], { :convention => :stdcall }) do |wnd, param|
  title.clear
  Win.get_window_text(wnd, title, title.size)
  puts "[%03i] Found '%s'" % [ win_count += 1, title.get_string(0) ]
  true
end

Try with both :convention => :stdcall and :convention => :default and see if it changes anything.

If it works with :stdcall, it means JRuby is not propagating the :stdcall all the way down to libffi, but should be (somewhat) easy to fix.

Show
Wayne Meissner added a comment - I wonder if this isn't a calling convention problem. Basically the callback may not be getting setup as :stdcall ... or it is when it isn't supposed to be. Try using a FFI::Function ( http://ffi.github.com/api/FFI/Function.html ) instead of a proc for the callback. e.g. Win::EnumWindowCallback = FFI::Function.new(:bool, [ :pointer, :long ], { :convention => :stdcall }) do |wnd, param| title.clear Win.get_window_text(wnd, title, title.size) puts "[%03i] Found '%s'" % [ win_count += 1, title.get_string(0) ] true end Try with both :convention => :stdcall and :convention => :default and see if it changes anything. If it works with :stdcall, it means JRuby is not propagating the :stdcall all the way down to libffi, but should be (somewhat) easy to fix.
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Roger Pack added a comment - - edited

it seems to work great with :convention => :stdcall and crash for anything else.

Looks like a good signature is:

FFI::Function.new(:bool, [ :long, :pointer ], { :convention => :stdcall }) do |hwnd, param|

Show
Roger Pack added a comment - - edited it seems to work great with :convention => :stdcall and crash for anything else. Looks like a good signature is: FFI::Function.new(:bool, [ :long, :pointer ], { :convention => :stdcall }) do |hwnd, param|
Charles Oliver Nutter made changes -
Field Original Value New Value
Component/s Extensions [ 12281 ]
Component/s Windows [ 13600 ]
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Roger Pack added a comment -

This is still reproducible using the gist.

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Roger Pack added a comment - This is still reproducible using the gist.

People

  • Assignee:
    Thomas E Enebo
    Reporter:
    Roger Pack
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Dates

  • Created:
    Updated: