Segfault on wrapper.rb:121 get_array_of_string

[danhealy]

I am getting this segfault pretty often, mac os x running rrdtool 1.4.4, rvm'd ruby 1.9.2-p136. The code that is executing is a series of consecutive rrd.fetch instructions. It is fairly reproducible (it happens almost every time I try a few things), but I haven't found a specific sequence that causes it. In particular, none of the steps on their own cause the segfault, it just happens.

/Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/rrd-ffi-0.2.7/lib/rrd/wrapper.rb:121: [BUG] Segmentation fault
ruby 1.9.2p136 (2010-12-25 revision 30365) [x86_64-darwin10.6.0]

-- control frame ----------
c:0043 p:---- s:0223 b:0223 l:000222 d:000222 CFUNC  :get_array_of_string
c:0042 p:0235 s:0218 b:0218 l:000217 d:000217 METHOD /Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/rrd-ffi-0.2.7/lib/rrd/wrapper.rb:121
c:0041 p:0167 s:0199 b:0199 l:000198 d:000198 METHOD /Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/rrd-ffi-0.2.7/lib/rrd/base.rb:52
c:0040 p:0141 s:0193 b:0193 l:000192 d:000192 METHOD /sandbox/skycharts/lib/skycharts.rb:183
c:0039 p:0286 s:0182 b:0182 l:0014f8 d:000181 LAMBDA webapp.rb:92
c:0038 p:---- s:0174 b:0174 l:000173 d:000173 FINISH
c:0037 p:---- s:0172 b:0172 l:000171 d:000171 CFUNC  :call
c:0036 p:0018 s:0169 b:0169 l:002620 d:000168 BLOCK  /Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:1165
c:0035 p:---- s:0167 b:0167 l:000166 d:000166 FINISH
c:0034 p:---- s:0165 b:0165 l:000164 d:000164 CFUNC  :instance_eval
c:0033 p:0016 s:0162 b:0160 l:000159 d:000159 METHOD /Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:738
c:0032 p:0012 s:0156 b:0156 l:000124 d:000155 BLOCK  /Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:722
c:0031 p:0017 s:0154 b:0154 l:000145 d:000153 BLOCK  /Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:772
c:0030 p:---- s:0152 b:0152 l:000151 d:000151 FINISH
c:0029 p:---- s:0150 b:0150 l:000149 d:000149 CFUNC  :catch
c:0028 p:0203 s:0146 b:0146 l:000145 d:000145 METHOD /Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:769
c:0027 p:0018 s:0136 b:0136 l:000124 d:000135 BLOCK  /Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:721
c:0026 p:---- s:0130 b:0130 l:000129 d:000129 FINISH
c:0025 p:---- s:0128 b:0128 l:000127 d:000127 CFUNC  :each
c:0024 p:0050 s:0125 b:0125 l:000124 d:000124 METHOD /Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:720
c:0023 p:0078 s:0119 b:0119 l:000118 d:000118 METHOD /Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:857
c:0022 p:0009 s:0115 b:0115 l:0007e8 d:000114 BLOCK  /Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:648
c:0021 p:---- s:0113 b:0113 l:000112 d:000112 FINISH
c:0020 p:---- s:0111 b:0111 l:000110 d:000110 CFUNC  :instance_eval
c:0019 p:0012 s:0108 b:0108 l:000099 d:000107 BLOCK  /Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:822
c:0018 p:---- s:0106 b:0106 l:000105 d:000105 FINISH
c:0017 p:---- s:0104 b:0104 l:000103 d:000103 CFUNC  :catch
c:0016 p:0013 s:0100 b:0100 l:000099 d:000099 METHOD /Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:822
c:0015 p:0155 s:0093 b:0093 l:0007e8 d:0007e8 METHOD /Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:648
c:0014 p:0019 s:0086 b:0086 l:000085 d:000085 METHOD /Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:633
c:0013 p:0032 s:0082 b:0082 l:000081 d:000081 METHOD /Users/dan/.rvm/gems/ruby-1.9.2-p136@global/gems/rack-1.2.2/lib/rack/commonlogger.rb:18
c:0012 p:0015 s:0074 b:0074 l:000073 d:000073 METHOD /Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/showexceptions.rb:21
c:0011 p:0155 s:0066 b:0066 l:000065 d:000065 METHOD /Users/dan/.rvm/gems/ruby-1.9.2-p136@global/gems/rack-1.2.2/lib/rack/methodoverride.rb:24
c:0010 p:0018 s:0060 b:0060 l:002550 d:000059 BLOCK  /Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:1284
c:0009 p:0032 s:0058 b:0058 l:000057 d:000057 METHOD /Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:1315
c:0008 p:0011 s:0054 b:0054 l:002550 d:002550 METHOD /Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:1284
c:0007 p:0015 s:0050 b:0050 l:000049 d:000049 METHOD /Users/dan/.rvm/gems/ruby-1.9.2-p136@global/gems/rack-1.2.2/lib/rack/content_length.rb:13
c:0006 p:0338 s:0042 b:0042 l:000041 d:000041 METHOD /Users/dan/.rvm/gems/ruby-1.9.2-p136@global/gems/rack-1.2.2/lib/rack/handler/webrick.rb:52
c:0005 p:0257 s:0030 b:0030 l:000029 d:000029 METHOD /Users/dan/.rvm/rubies/ruby-1.9.2-p136/lib/ruby/1.9.1/webrick/httpserver.rb:111
c:0004 p:0393 s:0020 b:0020 l:000019 d:000019 METHOD /Users/dan/.rvm/rubies/ruby-1.9.2-p136/lib/ruby/1.9.1/webrick/httpserver.rb:70
c:0003 p:0126 s:0009 b:0009 l:001c48 d:000008 BLOCK  /Users/dan/.rvm/rubies/ruby-1.9.2-p136/lib/ruby/1.9.1/webrick/server.rb:183
c:0002 p:---- s:0004 b:0004 l:000003 d:000003 FINISH
c:0001 p:---- s:0002 b:0002 l:000001 d:000001 TOP   
---------------------------
-- Ruby level backtrace information ----------------------------------------
/Users/dan/.rvm/rubies/ruby-1.9.2-p136/lib/ruby/1.9.1/webrick/server.rb:183:in `block in start_thread'
/Users/dan/.rvm/rubies/ruby-1.9.2-p136/lib/ruby/1.9.1/webrick/httpserver.rb:70:in `run'
/Users/dan/.rvm/rubies/ruby-1.9.2-p136/lib/ruby/1.9.1/webrick/httpserver.rb:111:in `service'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@global/gems/rack-1.2.2/lib/rack/handler/webrick.rb:52:in `service'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@global/gems/rack-1.2.2/lib/rack/content_length.rb:13:in `call'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:1284:in `call'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:1315:in `synchronize'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:1284:in `block in call'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@global/gems/rack-1.2.2/lib/rack/methodoverride.rb:24:in `call'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/showexceptions.rb:21:in `call'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@global/gems/rack-1.2.2/lib/rack/commonlogger.rb:18:in `call'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:633:in `call'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:648:in `call!'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:822:in `invoke'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:822:in `catch'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:822:in `block in invoke'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:822:in `instance_eval'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:648:in `block in call!'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:857:in `dispatch!'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:720:in `route!'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:720:in `each'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:721:in `block in route!'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:769:in `process_route'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:769:in `catch'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:772:in `block in process_route'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:722:in `block (2 levels) in route!'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:738:in `route_eval'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:738:in `instance_eval'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:1165:in `block in compile!'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/sinatra-1.2.3/lib/sinatra/base.rb:1165:in `call'
webapp.rb:92:in `block in <main>'
/sandbox/skycharts/lib/skycharts.rb:183:in `fetch_time_data'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/rrd-ffi-0.2.7/lib/rrd/base.rb:52:in `fetch'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/rrd-ffi-0.2.7/lib/rrd/wrapper.rb:121:in `fetch'
/Users/dan/.rvm/gems/ruby-1.9.2-p136@skycharts/gems/rrd-ffi-0.2.7/lib/rrd/wrapper.rb:121:in `get_array_of_string'

-- C level backtrace information -------------------------------------------

[NOTE]
You may have encountered a bug in the Ruby interpreter or extension libraries.
Bug reports are welcome.
For details: http://www.ruby-lang.org/bugreport.html

Abort trap

[danhealy]

I think I figured this one out. If I wrap the call to .fetch around a mutex, it works fine. Is this obvious and I just missed it, or should it be documented?

[morellon]

Sorry for the delay. A mutex shouldn't be needed, supposing rrd_fetch function from librrd is thread safe. I will check librrd for a thread safe function, I know some functions have both thread-safe ad non thread-safe versions. You said it was not happening in one specific step, but can you check if it has something to do with get_array_of_string or from_string methods? Also, which version of ffi are you using?

[danhealy]

It breaks on the same line every time without the mutex, wrapper.rb line 121. Using ffi 1.0.7. Thanks for looking into it.

[danhealy]

I was referring to the order of RRDs accessed when I mentioned it didn't happen at any specific step. The segfault is in the same place.

[neilljordan]

I'm encountering the same segfault in get_array_of_string. Did you find a resolution for this issue?

[danhealy]

Looks like there haven't been any code changes since I opened this issue. My code works by wrapping the call to .fetch with a mutex: http://www.ruby-doc.org/core/classes/Mutex.html

[morellon]

Sorry guys, I didn't have enough time to look into this issue

[morellon]

As I could see. There seems to be a thread safe version of the function. I will code based on it. The function is the following: int rrd_fetch_r ( const char _filename, const char cf, time_t start, time_t end, unsigned long step, unsigned long ds_cnt, char __ds_namv, rrd_value_t *_data);

[morellon]

Hi Guys, I just implemented the fetch using rrd_fetch_r. Could you checkout from the master and test if the issue continues?

[morellon]

Well, I will close this issue. If needed please open a new one.