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Use signal to show stacktrace of a Ruby process without restarting it

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# sigdump

In short: *SIGQUIT of Java VM for Ruby.*

Server applications (like Rails apps) cause performance problems, deadlock or memory swapping from time to time. But it's difficult to reproduce such kind of problems. `sigdump` makes it possible to get information from a running process without restarting. Just sending `SIGCONT` signal will dump backtrace and memory profile to `/tmp/sigdump-<pid>.log` file.

`sigdump` dumps following information (see also [Sample output](#sample-outout)):

* Backtrace of all threads
* Number of allocated objects per class
* GC profiler reports if GC profiler is enabled (`GC::Profiler.enable` is called)
* Stacktrace of Java threads for each Ruby threads if the runtime is JRuby

## Install

Just install `sigdump` gem and add `require 'sigdump/setup'` line to your code. Or you can use Bundler as following:

```ruby
# Gemfile
gem 'sigdump', require: 'sigdump/setup'
```

Note for [Resque](https://github.com/resque/resque):

You need to change the default signal (`SIGCONT`) because Rescue traps `SIGCONT` and it conflicts with sigdump.
To change the signal, set name of a signal to `SIGDUMP_SIGNAL` environment variable. For Rails, you can add following lines to `environment.rb` file:

```ruby
# setup sigdump: https://github.com/frsyuki/sigdump
ENV['SIGDUMP_SIGNAL'] = 'TSTP'
require 'sigdump/setup'
```

## Usage

Send `SIGCONT` signal to the Ruby process. It dumps backtrace and memory profile to `/tmp/sigdump-<pid>.log` file.

```shell
$ kill -CONT <pid>
$ cat /tmp/sigdump-<pid>.log
```

Set `SIGDUMP_SIGNAL` environment variable to change the signal (default: SIGCONT).

Set `SIGDUMP_PATH` environment variable to change the output path (default: /tmp/sigdump-\<pid\>.log). You can set "-" here to dump to STDOUT, or "+" to STDERR.

## Sample outout

$ cat /tmp/sigdump-9218.log
    Sigdump at 2013-04-24 16:57:12 +0000 process 9218 (unicorn worker[3] -E staging -c /etc/unicorn/staging.rb -E staging)
      Thread #<Thread:0x00000001424518> status=run priority=0
          /srv/staging/current/vendor/bundle/ruby/1.9.1/gems/sigdump-0.1.0/lib/sigdump.rb:32:in `dump_backtrace'
          /srv/staging/current/vendor/bundle/ruby/1.9.1/gems/sigdump-0.1.0/lib/sigdump.rb:19:in `block in dump_all_thread_backtrace'
          /srv/staging/current/vendor/bundle/ruby/1.9.1/gems/sigdump-0.1.0/lib/sigdump.rb:18:in `each'
          /srv/staging/current/vendor/bundle/ruby/1.9.1/gems/sigdump-0.1.0/lib/sigdump.rb:18:in `dump_all_thread_backtrace'
          /srv/staging/current/vendor/bundle/ruby/1.9.1/gems/sigdump-0.1.0/lib/sigdump.rb:9:in `block (2 levels) in install_thread_dump_handler'
          /srv/staging/current/vendor/bundle/ruby/1.9.1/gems/sigdump-0.1.0/lib/sigdump.rb:91:in `open'
          /srv/staging/current/vendor/bundle/ruby/1.9.1/gems/sigdump-0.1.0/lib/sigdump.rb:91:in `_open_dump_path'
          /srv/staging/current/vendor/bundle/ruby/1.9.1/gems/sigdump-0.1.0/lib/sigdump.rb:7:in `block in install_thread_dump_handler'
          /srv/staging/current/vendor/bundle/ruby/1.9.1/gems/unicorn-4.3.1/lib/unicorn/http_server.rb:626:in `call'
          /srv/staging/current/vendor/bundle/ruby/1.9.1/gems/unicorn-4.3.1/lib/unicorn/http_server.rb:626:in `select'
          /srv/staging/current/vendor/bundle/ruby/1.9.1/gems/unicorn-4.3.1/lib/unicorn/http_server.rb:626:in `worker_loop'
          /srv/staging/current/vendor/bundle/ruby/1.9.1/gems/unicorn-4.3.1/lib/unicorn/http_server.rb:487:in `spawn_missing_workers'
          /srv/staging/current/vendor/bundle/ruby/1.9.1/gems/unicorn-4.3.1/lib/unicorn/http_server.rb:137:in `start'
          /srv/staging/current/vendor/bundle/ruby/1.9.1/gems/unicorn-4.3.1/bin/unicorn:121:in `<top (required)>'
          /srv/staging/current/vendor/bundle/ruby/1.9.1/bin/unicorn:23:in `load'
          /srv/staging/current/vendor/bundle/ruby/1.9.1/bin/unicorn:23:in `<main>'
      GC stat:
          count: 34
          heap_allocated_pages: 1366
          heap_sorted_length: 1368
          heap_allocatable_pages: 0
          heap_available_slots: 556777
          heap_live_slots: 551708
          heap_free_slots: 5069
          heap_final_slots: 0
          heap_marked_slots: 363350
          heap_swept_slots: 58807
          heap_eden_pages: 1366
          heap_tomb_pages: 0
          total_allocated_pages: 1367
          total_freed_pages: 1
          total_allocated_objects: 2438499
          total_freed_objects: 1886791
          malloc_increase_bytes: 650416
          malloc_increase_bytes_limit: 16777216
          minor_gc_count: 25
          major_gc_count: 9
          remembered_wb_unprotected_objects: 5122
          remembered_wb_unprotected_objects_limit: 5222
          old_objects: 348964
      Built-in objects:
       367,492: TOTAL
       208,193: T_STRING
        61,817: T_ARRAY
        37,343: T_DATA
        28,293: T_NODE
        10,678: T_OBJECT
         6,385: T_HASH
         5,957: T_CLASS
         2,300: T_ICLASS
         2,184: T_REGEXP
         1,547: T_MODULE
           900: T_FLOAT
           677: T_STRUCT
           497: T_BIGNUM
           432: T_MATCH
           251: T_RATIONAL
            29: T_FILE
             8: FREE
             1: T_COMPLEX
      All objects:
       207,335: String
        32,987: Array
        28,665: RubyVM::InstructionSequence
         5,863: Hash
         3,759: RubyVM::Env
         3,680: Proc
         2,338: Class
         2,184: Regexp
         1,632: MIME::Type
         1,547: Module
         1,040: Gem::Version
           982: Gem::Requirement
           945: Float
           920: Journey::Nodes::Cat
           804: Time
           660: Gem::Dependency
           497: Bignum
      ...
      String 7,556,137 bytes
       Array 821 elements
        Hash 90 pairs

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