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Update debugging guide to use byebug

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David Rodríguez de Dios 2014-04-08 20:59:28 +02:00
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423
guides/source/debugging_rails_applications.md
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@ -240,57 +240,69 @@ The contents of the block, and therefore the string interpolation, is only
evaluated if debug is enabled. This performance savings is only really
noticeable with large amounts of logging, but it's a good practice to employ.
Debugging with the `debugger` gem
Debugging with the `byebug` gem
---------------------------------
When your code is behaving in unexpected ways, you can try printing to logs or the console to diagnose the problem. Unfortunately, there are times when this sort of error tracking is not effective in finding the root cause of a problem. When you actually need to journey into your running source code, the debugger is your best companion.
When your code is behaving in unexpected ways, you can try printing to logs or
the console to diagnose the problem. Unfortunately, there are times when this
sort of error tracking is not effective in finding the root cause of a problem.
When you actually need to journey into your running source code, the debugger
is your best companion.
The debugger can also help you if you want to learn about the Rails source code but don't know where to start. Just debug any request to your application and use this guide to learn how to move from the code you have written deeper into Rails code.
The debugger can also help you if you want to learn about the Rails source code
but don't know where to start. Just debug any request to your application and
use this guide to learn how to move from the code you have written deeper into
Rails code.
### Setup
You can use the `debugger` gem to set breakpoints and step through live code in Rails. To install it, just run:
You can use the `byebug` gem to set breakpoints and step through live code in
Rails. To install it, just run:
```bash
$ gem install debugger
$ gem install byebug
```
Rails has had built-in support for debugging since Rails 2.0. Inside any Rails application you can invoke the debugger by calling the `debugger` method.
Inside any Rails application you can then invoke the debugger by calling the
`byebug` method.
Here's an example:
```ruby
class PeopleController < ApplicationController
def new
debugger
byebug
@person = Person.new
end
end
```
If you see this message in the console or logs:
```
***** Debugger requested, but was not available: Start server with --debugger to enable *****
```
Make sure you have started your web server with the option `--debugger`:
```bash
$ rails server --debugger
=> Booting WEBrick
=> Rails 4.0.0 application starting on http://0.0.0.0:3000
=> Debugger enabled
...
```
TIP: In development mode, you can dynamically `require \'debugger\'` instead of restarting the server, even if it was started without `--debugger`.
### The Shell
As soon as your application calls the `debugger` method, the debugger will be started in a debugger shell inside the terminal window where you launched your application server, and you will be placed at the debugger's prompt `(rdb:n)`. The _n_ is the thread number. The prompt will also show you the next line of code that is waiting to run.
As soon as your application calls the `byebug` method, the debugger will be
started in a debugger shell inside the terminal window where you launched your
application server, and you will be placed at the debugger's prompt `(byebug)`.
Before the prompt, the code around the line that is about to be run will be
shown and the current line is marked by '=>'. Like this:
If you got there by a browser request, the browser tab containing the request will be hung until the debugger has finished and the trace has finished processing the entire request.
```
[1, 10] in /PathTo/project/app/controllers/posts_controller.rb
1 class PostsController < ApplicationController
2 # GET /posts
3 # GET /posts.json
4 def index
5 byebug
=> 6 @posts = Post.all
7
8 respond_to do |format|
9 format.html # index.html.erb
10 format.json { render json: @posts }
(byebug)
```
If you got there by a browser request, the browser tab containing the request
will be hung until the debugger has finished and the trace has finished
processing the entire request.
For example:
@ -299,71 +311,38 @@ For example:
(rdb:7)
```
Now it's time to explore and dig into your application. A good place to start is by asking the debugger for help. Type: `help`
Now it's time to explore and dig into your application. A good place to start is
by asking the debugger for help. Type: `help`
```
(rdb:7) help
ruby-debug help v0.10.2
(byebug) help
byebug 2.6.0
Type 'help <command-name>' for help on a specific command
Available commands:
backtrace delete enable help next quit show trace
break disable eval info p reload source undisplay
catch display exit irb pp restart step up
condition down finish list ps save thread var
continue edit frame method putl set tmate where
backtrace delete enable help list pry next restart source up
break disable eval info method ps save step var
catch display exit interrupt next putl set thread
condition down finish irb p quit show trace
continue edit frame kill pp reload skip undisplay
```
TIP: To view the help menu for any command use `help <command-name>` at the debugger prompt. For example: _`help var`_
TIP: To view the help menu for any command use `help <command-name>` at the
debugger prompt. For example: _`help list`_. You can abbreviate any debugging
command by supplying just enough letters to distinguish them from other
commands, so you can also use `l` for the `list` command, for example.
The next command to learn is one of the most useful: `list`. You can abbreviate any debugging command by supplying just enough letters to distinguish them from other commands, so you can also use `l` for the `list` command.
This command shows you where you are in the code by printing 10 lines centered around the current line; the current line in this particular case is line 6 and is marked by `=>`.
To see the previous ten lines you should type `list-` (or `l-`)
```
(rdb:7) list
(byebug) l-
[1, 10] in /PathTo/project/app/controllers/posts_controller.rb
1 class PostsController < ApplicationController
2 # GET /posts
3 # GET /posts.json
4 def index
5 debugger
=> 6 @posts = Post.all
7
8 respond_to do |format|
9 format.html # index.html.erb
10 format.json { render json: @posts }
```
If you repeat the `list` command, this time using just `l`, the next ten lines of the file will be printed out.
```
(rdb:7) l
[11, 20] in /PathTo/project/app/controllers/posts_controller.rb
11 end
12 end
13
14 # GET /posts/1
15 # GET /posts/1.json
16 def show
17 @post = Post.find(params[:id])
18
19 respond_to do |format|
20 format.html # show.html.erb
```
And so on until the end of the current file. When the end of file is reached, the `list` command will start again from the beginning of the file and continue again up to the end, treating the file as a circular buffer.
On the other hand, to see the previous ten lines you should type `list-` (or `l-`)
```
(rdb:7) l-
[1, 10] in /PathTo/project/app/controllers/posts_controller.rb
1 class PostsController < ApplicationController
2 # GET /posts
3 # GET /posts.json
4 def index
5 debugger
5 byebug
6 @posts = Post.all
7
8 respond_to do |format|
@ -371,17 +350,18 @@ On the other hand, to see the previous ten lines you should type `list-` (or `l-
10 format.json { render json: @posts }
```
This way you can move inside the file, being able to see the code above and over the line you added the `debugger`.
Finally, to see where you are in the code again you can type `list=`
This way you can move inside the file, being able to see the code above and over
the line you added the `byebug` call. Finally, to see where you are in the code
again you can type `list=`
```
(rdb:7) list=
(byebug) list=
[1, 10] in /PathTo/project/app/controllers/posts_controller.rb
1 class PostsController < ApplicationController
2 # GET /posts
3 # GET /posts.json
4 def index
5 debugger
5 byebug
=> 6 @posts = Post.all
7
8 respond_to do |format|
@ -391,14 +371,22 @@ Finally, to see where you are in the code again you can type `list=`
### The Context
When you start debugging your application, you will be placed in different contexts as you go through the different parts of the stack.
When you start debugging your application, you will be placed in different
contexts as you go through the different parts of the stack.
The debugger creates a context when a stopping point or an event is reached. The context has information about the suspended program which enables a debugger to inspect the frame stack, evaluate variables from the perspective of the debugged program, and contains information about the place where the debugged program is stopped.
The debugger creates a context when a stopping point or an event is reached. The
context has information about the suspended program which enables the debugger
to inspect the frame stack, evaluate variables from the perspective of the
debugged program, and contains information about the place where the debugged
program is stopped.
At any time you can call the `backtrace` command (or its alias `where`) to print the backtrace of the application. This can be very helpful to know how you got where you are. If you ever wondered about how you got somewhere in your code, then `backtrace` will supply the answer.
At any time you can call the `backtrace` command (or its alias `where`) to print
the backtrace of the application. This can be very helpful to know how you got
where you are. If you ever wondered about how you got somewhere in your code,
then `backtrace` will supply the answer.
```
(rdb:5) where
(byebug) where
#0 PostsController.index
at line /PathTo/project/app/controllers/posts_controller.rb:6
#1 Kernel.send
@ -410,46 +398,64 @@ At any time you can call the `backtrace` command (or its alias `where`) to print
...
```
You move anywhere you want in this trace (thus changing the context) by using the `frame _n_` command, where _n_ is the specified frame number.
You move anywhere you want in this trace (thus changing the context) by using
the `frame _n_` command, where _n_ is the specified frame number.
```
(rdb:5) frame 2
(byebug) frame 2
#2 ActionController::Base.perform_action_without_filters
at line /PathTo/project/vendor/rails/actionpack/lib/action_controller/base.rb:1175
```
The available variables are the same as if you were running the code line by line. After all, that's what debugging is.
The available variables are the same as if you were running the code line by
line. After all, that's what debugging is.
Moving up and down the stack frame: You can use `up [n]` (`u` for abbreviated) and `down [n]` commands in order to change the context _n_ frames up or down the stack respectively. _n_ defaults to one. Up in this case is towards higher-numbered stack frames, and down is towards lower-numbered stack frames.
Moving up and down the stack frame: You can use `up [n]` (`u` for abbreviated)
and `down [n]` commands in order to change the context _n_ frames up or down the
stack respectively. _n_ defaults to one. Up in this case is towards
higher-numbered stack frames, and down is towards lower-numbered stack frames.
### Threads
The debugger can list, stop, resume and switch between running threads by using the command `thread` (or the abbreviated `th`). This command has a handful of options:
The debugger can list, stop, resume and switch between running threads by using
the command `thread` (or the abbreviated `th`). This command has a handful of
options:
* `thread` shows the current thread.
* `thread list` is used to list all threads and their statuses. The plus + character and the number indicates the current thread of execution.
* `thread list` is used to list all threads and their statuses. The plus +
character and the number indicates the current thread of execution.
* `thread stop _n_` stop thread _n_.
* `thread resume _n_` resumes thread _n_.
* `thread switch _n_` switches the current thread context to _n_.
This command is very helpful, among other occasions, when you are debugging concurrent threads and need to verify that there are no race conditions in your code.
This command is very helpful, among other occasions, when you are debugging
concurrent threads and need to verify that there are no race conditions in your
code.
### Inspecting Variables
Any expression can be evaluated in the current context. To evaluate an expression, just type it!
Any expression can be evaluated in the current context. To evaluate an
expression, just type it!
This example shows how you can print the instance_variables defined within the current context:
This example shows how you can print the instance_variables defined within the
current context:
```
@posts = Post.all
(rdb:11) instance_variables
["@_response", "@action_name", "@url", "@_session", "@_cookies", "@performed_render", "@_flash", "@template", "@_params", "@before_filter_chain_aborted", "@request_origin", "@_headers", "@performed_redirect", "@_request"]
(byebug) instance_variables
["@_response", "@action_name", "@url", "@_session", "@_cookies",
"@performed_render", "@_flash", "@template", "@_params",
"@before_filter_chain_aborted", "@request_origin", "@_headers",
"@performed_redirect", "@_request"]
```
As you may have figured out, all of the variables that you can access from a controller are displayed. This list is dynamically updated as you execute code. For example, run the next line using `next` (you'll learn more about this command later in this guide).
As you may have figured out, all of the variables that you can access from a
controller are displayed. This list is dynamically updated as you execute code.
For example, run the next line using `next` (you'll learn more about this
command later in this guide).
```
(rdb:11) next
(byebug) next
Processing PostsController#index (for 127.0.0.1 at 2008-09-04 19:51:34) [GET]
Session ID: BAh7BiIKZmxhc2hJQzonQWN0aW9uQ29udHJvbGxlcjo6Rmxhc2g6OkZsYXNoSGFzaHsABjoKQHVzZWR7AA==--b16e91b992453a8cc201694d660147bba8b0fd0e
Parameters: {"action"=>"index", "controller"=>"posts"}
@ -460,64 +466,80 @@ respond_to do |format|
And then ask again for the instance_variables:
```
(rdb:11) instance_variables.include? "@posts"
(byebug) instance_variables.include? "@posts"
true
```
Now `@posts` is included in the instance variables, because the line defining it was executed.
Now `@posts` is included in the instance variables, because the line defining it
was executed.
TIP: You can also step into **irb** mode with the command `irb` (of course!). This way an irb session will be started within the context you invoked it. But be warned: this is an experimental feature.
TIP: You can also step into **irb** mode with the command `irb` (of course!).
This way an irb session will be started within the context you invoked it. But
be warned: this is an experimental feature.
The `var` method is the most convenient way to show variables and their values:
```
var
(rdb:1) v[ar] const <object> show constants of object
(rdb:1) v[ar] g[lobal] show global variables
(rdb:1) v[ar] i[nstance] <object> show instance variables of object
(rdb:1) v[ar] l[ocal] show local variables
(byebug) v[ar] const <object> show constants of object
(byebug) v[ar] g[lobal] show global variables
(byebug) v[ar] i[nstance] <object> show instance variables of object
(byebug) v[ar] l[ocal] show local variables
```
This is a great way to inspect the values of the current context variables. For example:
This is a great way to inspect the values of the current context variables. For
example:
```
(rdb:9) var local
(byebug) var local
__dbg_verbose_save => false
```
You can also inspect for an object method this way:
```
(rdb:9) var instance Post.new
(byebug) var instance Post.new
@attributes = {"updated_at"=>nil, "body"=>nil, "title"=>nil, "published"=>nil, "created_at"...
@attributes_cache = {}
@new_record = true
```
TIP: The commands `p` (print) and `pp` (pretty print) can be used to evaluate Ruby expressions and display the value of variables to the console.
TIP: The commands `p` (print) and `pp` (pretty print) can be used to evaluate
Ruby expressions and display the value of variables to the console.
You can use also `display` to start watching variables. This is a good way of tracking the values of a variable while the execution goes on.
You can use also `display` to start watching variables. This is a good way of
tracking the values of a variable while the execution goes on.
```
(rdb:1) display @recent_comments
(byebug) display @recent_comments
1: @recent_comments =
```
The variables inside the displaying list will be printed with their values after you move in the stack. To stop displaying a variable use `undisplay _n_` where _n_ is the variable number (1 in the last example).
The variables inside the displaying list will be printed with their values after
you move in the stack. To stop displaying a variable use `undisplay _n_` where
_n_ is the variable number (1 in the last example).
### Step by Step
Now you should know where you are in the running trace and be able to print the available variables. But lets continue and move on with the application execution.
Now you should know where you are in the running trace and be able to print the
available variables. But lets continue and move on with the application
execution.
Use `step` (abbreviated `s`) to continue running your program until the next logical stopping point and return control to the debugger.
Use `step` (abbreviated `s`) to continue running your program until the next
logical stopping point and return control to the debugger.
TIP: You can also use `step+ n` and `step- n` to move forward or backward `n` steps respectively.
TIP: You can also use `step+ n` and `step- n` to move forward or backward `n`
steps respectively.
You may also use `next` which is similar to step, but function or method calls that appear within the line of code are executed without stopping. As with step, you may use plus sign to move _n_ steps.
You may also use `next` which is similar to step, but function or method calls
that appear within the line of code are executed without stopping. As with
`step`, you may use plus sign to move _n_ steps.
The difference between `next` and `step` is that `step` stops at the next line of code executed, doing just a single step, while `next` moves to the next line without descending inside methods.
The difference between `next` and `step` is that `step` stops at the next line
of code executed, doing just a single step, while `next` moves to the next line
without descending inside methods.
For example, consider this block of code with an included `debugger` statement:
For example, consider this block of code with an included `byebug` statement:
```ruby
class Author < ActiveRecord::Base
@ -525,53 +547,46 @@ class Author < ActiveRecord::Base
has_many :comments
def find_recent_comments(limit = 10)
debugger
byebug
@recent_comments ||= comments.where("created_at > ?", 1.week.ago).limit(limit)
end
end
```
TIP: You can use the debugger while using `rails console`. Just remember to `require "debugger"` before calling the `debugger` method.
```
$ rails console
Loading development environment (Rails 4.0.0)
>> require "debugger"
=> []
>> author = Author.first
=> #<Author id: 1, first_name: "Bob", last_name: "Smith", created_at: "2008-07-31 12:46:10", updated_at: "2008-07-31 12:46:10">
>> author.find_recent_comments
/PathTo/project/app/models/author.rb:11
)
```
With the code stopped, take a look around:
```
(rdb:1) list
[2, 9] in /PathTo/project/app/models/author.rb
2 has_one :editorial
3 has_many :comments
4
5 def find_recent_comments(limit = 10)
6 debugger
6 byebug
=> 7 @recent_comments ||= comments.where("created_at > ?", 1.week.ago).limit(limit)
8 end
9 end
(byebug)
```
You are at the end of the line, but... was this line executed? You can inspect the instance variables.
You are at the end of the line, but... was this line executed? You can inspect
the instance variables.
```
(rdb:1) var instance
(byebug) var instance
@attributes = {"updated_at"=>"2008-07-31 12:46:10", "id"=>"1", "first_name"=>"Bob", "las...
@attributes_cache = {}
```
`@recent_comments` hasn't been defined yet, so it's clear that this line hasn't been executed yet. Use the `next` command to move on in the code:
`@recent_comments` hasn't been defined yet, so it's clear that this line hasn't
been executed yet. Use the `next` command to move on in the code:
```
(rdb:1) next
(byebug) next
/PathTo/project/app/models/author.rb:12
@recent_comments
(rdb:1) var instance
@ -581,89 +596,119 @@ You are at the end of the line, but... was this line executed? You can inspect t
@recent_comments = []
```
Now you can see that the `@comments` relationship was loaded and @recent_comments defined because the line was executed.
Now you can see that the `@comments` relationship was loaded and
`@recent_comments` defined because the line was executed.
If you want to go deeper into the stack trace you can move single `steps`, through your calling methods and into Rails code. This is one of the best ways to find bugs in your code, or perhaps in Ruby or Rails.
If you want to go deeper into the stack trace you can move single steps
through your calling methods and into Rails code. This is one of the best ways
to find bugs in your code, or perhaps in Ruby or Rails.
### Breakpoints
A breakpoint makes your application stop whenever a certain point in the program is reached. The debugger shell is invoked in that line.
A breakpoint makes your application stop whenever a certain point in the program
is reached. The debugger shell is invoked in that line.
You can add breakpoints dynamically with the command `break` (or just `b`). There are 3 possible ways of adding breakpoints manually:
You can add breakpoints dynamically with the command `break` (or just `b`).
There are 3 possible ways of adding breakpoints manually:
* `break line`: set breakpoint in the _line_ in the current source file.
* `break file:line [if expression]`: set breakpoint in the _line_ number inside the _file_. If an _expression_ is given it must evaluated to _true_ to fire up the debugger.
* `break class(.|\#)method [if expression]`: set breakpoint in _method_ (. and \# for class and instance method respectively) defined in _class_. The _expression_ works the same way as with file:line.
* `break file:line [if expression]`: set breakpoint in the _line_ number inside
the _file_. If an _expression_ is given it must evaluated to _true_ to fire up
the debugger.
* `break class(.|\#)method [if expression]`: set breakpoint in _method_ (. and
\# for class and instance method respectively) defined in _class_. The
_expression_ works the same way as with file:line.
```
(rdb:5) break 10
(byebug:5) break 10
Breakpoint 1 file /PathTo/project/vendor/rails/actionpack/lib/action_controller/filters.rb, line 10
```
Use `info breakpoints _n_` or `info break _n_` to list breakpoints. If you supply a number, it lists that breakpoint. Otherwise it lists all breakpoints.
Use `info breakpoints _n_` or `info break _n_` to list breakpoints. If you
supply a number, it lists that breakpoint. Otherwise it lists all breakpoints.
```
(rdb:5) info breakpoints
(byebug:5) info breakpoints
Num Enb What
1 y at filters.rb:10
```
To delete breakpoints: use the command `delete _n_` to remove the breakpoint number _n_. If no number is specified, it deletes all breakpoints that are currently active..
To delete breakpoints: use the command `delete _n_` to remove the breakpoint
number _n_. If no number is specified, it deletes all breakpoints that are
currently active.
```
(rdb:5) delete 1
(rdb:5) info breakpoints
(byebug:5) delete 1
(byebug:5) info breakpoints
No breakpoints.
```
You can also enable or disable breakpoints:
* `enable breakpoints`: allow a list _breakpoints_ or all of them if no list is specified, to stop your program. This is the default state when you create a breakpoint.
* `enable breakpoints`: allow a list _breakpoints_ or all of them if no list is
specified, to stop your program. This is the default state when you create a
breakpoint.
* `disable breakpoints`: the _breakpoints_ will have no effect on your program.
### Catching Exceptions
The command `catch exception-name` (or just `cat exception-name`) can be used to intercept an exception of type _exception-name_ when there would otherwise be is no handler for it.
The command `catch exception-name` (or just `cat exception-name`) can be used to
intercept an exception of type _exception-name_ when there would otherwise be no
handler for it.
To list all active catchpoints use `catch`.
### Resuming Execution
There are two ways to resume execution of an application that is stopped in the debugger:
There are two ways to resume execution of an application that is stopped in the
debugger:
* `continue` [line-specification] \(or `c`): resume program execution, at the address where your script last stopped; any breakpoints set at that address are bypassed. The optional argument line-specification allows you to specify a line number to set a one-time breakpoint which is deleted when that breakpoint is reached.
* `finish` [frame-number] \(or `fin`): execute until the selected stack frame returns. If no frame number is given, the application will run until the currently selected frame returns. The currently selected frame starts out the most-recent frame or 0 if no frame positioning (e.g up, down or frame) has been performed. If a frame number is given it will run until the specified frame returns.
* `continue` [line-specification] \(or `c`): resume program execution, at the
address where your script last stopped; any breakpoints set at that address are
bypassed. The optional argument line-specification allows you to specify a line
number to set a one-time breakpoint which is deleted when that breakpoint is
reached.
* `finish` [frame-number] \(or `fin`): execute until the selected stack frame
returns. If no frame number is given, the application will run until the
currently selected frame returns. The currently selected frame starts out the
most-recent frame or 0 if no frame positioning (e.g up, down or frame) has been
performed. If a frame number is given it will run until the specified frame
returns.
### Editing
Two commands allow you to open code from the debugger into an editor:
* `edit [file:line]`: edit _file_ using the editor specified by the EDITOR environment variable. A specific _line_ can also be given.
* `tmate _n_` (abbreviated `tm`): open the current file in TextMate. It uses n-th frame if _n_ is specified.
* `edit [file:line]`: edit _file_ using the editor specified by the EDITOR
environment variable. A specific _line_ can also be given.
### Quitting
To exit the debugger, use the `quit` command (abbreviated `q`), or its alias `exit`.
To exit the debugger, use the `quit` command (abbreviated `q`), or its alias
`exit`.
A simple quit tries to terminate all threads in effect. Therefore your server will be stopped and you will have to start it again.
A simple quit tries to terminate all threads in effect. Therefore your server
will be stopped and you will have to start it again.
### Settings
The `debugger` gem can automatically show the code you're stepping through and reload it when you change it in an editor. Here are a few of the available options:
`byebug` has a few available options to tweak its behaviour:
* `set reload`: Reload source code when changed.
* `set autolist`: Execute `list` command on every breakpoint.
* `set listsize _n_`: Set number of source lines to list by default to _n_.
* `set forcestep`: Make sure the `next` and `step` commands always move to a new line
* `set autoreload`: Reload source code when changed (default: true).
* `set autolist`: Execute `list` command on every breakpoint (default: true).
* `set listsize _n_`: Set number of source lines to list by default to _n_
(default: 10)
* `set forcestep`: Make sure the `next` and `step` commands always move to a new
line.
You can see the full list by using `help set`. Use `help set _subcommand_` to learn about a particular `set` command.
You can see the full list by using `help set`. Use `help set _subcommand_` to
learn about a particular `set` command.
TIP: You can save these settings in an `.rdebugrc` file in your home directory. The debugger reads these global settings when it starts.
Here's a good start for an `.rdebugrc`:
TIP: You can save these settings in an `.byebugrc` file in your home directory.
The debugger reads these global settings when it starts. For example:
```bash
set autolist
set forcestep
set listsize 25
```
@ -671,35 +716,59 @@ set listsize 25
Debugging Memory Leaks
----------------------
A Ruby application (on Rails or not), can leak memory - either in the Ruby code or at the C code level.
A Ruby application (on Rails or not), can leak memory - either in the Ruby code
or at the C code level.
In this section, you will learn how to find and fix such leaks by using tool such as Valgrind.
In this section, you will learn how to find and fix such leaks by using tool
such as Valgrind.
### Valgrind
[Valgrind](http://valgrind.org/) is a Linux-only application for detecting C-based memory leaks and race conditions.
[Valgrind](http://valgrind.org/) is a Linux-only application for detecting
C-based memory leaks and race conditions.
There are Valgrind tools that can automatically detect many memory management and threading bugs, and profile your programs in detail. For example, if a C extension in the interpreter calls `malloc()` but doesn't properly call `free()`, this memory won't be available until the app terminates.
There are Valgrind tools that can automatically detect many memory management
and threading bugs, and profile your programs in detail. For example, if a C
extension in the interpreter calls `malloc()` but doesn't properly call
`free()`, this memory won't be available until the app terminates.
For further information on how to install Valgrind and use with Ruby, refer to [Valgrind and Ruby](http://blog.evanweaver.com/articles/2008/02/05/valgrind-and-ruby/) by Evan Weaver.
For further information on how to install Valgrind and use with Ruby, refer to
[Valgrind and Ruby](http://blog.evanweaver.com/articles/2008/02/05/valgrind-and-ruby/)
by Evan Weaver.
Plugins for Debugging
---------------------
There are some Rails plugins to help you to find errors and debug your application. Here is a list of useful plugins for debugging:
There are some Rails plugins to help you to find errors and debug your
application. Here is a list of useful plugins for debugging:
* [Footnotes](https://github.com/josevalim/rails-footnotes) Every Rails page has footnotes that give request information and link back to your source via TextMate.
* [Query Trace](https://github.com/ntalbott/query_trace/tree/master) Adds query origin tracing to your logs.
* [Query Reviewer](https://github.com/nesquena/query_reviewer) This rails plugin not only runs "EXPLAIN" before each of your select queries in development, but provides a small DIV in the rendered output of each page with the summary of warnings for each query that it analyzed.
* [Exception Notifier](https://github.com/smartinez87/exception_notification/tree/master) Provides a mailer object and a default set of templates for sending email notifications when errors occur in a Rails application.
* [Better Errors](https://github.com/charliesome/better_errors) Replaces the standard Rails error page with a new one containing more contextual information, like source code and variable inspection.
* [RailsPanel](https://github.com/dejan/rails_panel) Chrome extension for Rails development that will end your tailing of development.log. Have all information about your Rails app requests in the browser - in the Developer Tools panel. Provides insight to db/rendering/total times, parameter list, rendered views and more.
* [Footnotes](https://github.com/josevalim/rails-footnotes) Every Rails page has
footnotes that give request information and link back to your source via
TextMate.
* [Query Trace](https://github.com/ntalbott/query_trace/tree/master) Adds query
origin tracing to your logs.
* [Query Reviewer](https://github.com/nesquena/query_reviewer) This rails plugin
not only runs "EXPLAIN" before each of your select queries in development, but
provides a small DIV in the rendered output of each page with the summary of
warnings for each query that it analyzed.
* [Exception Notifier](https://github.com/smartinez87/exception_notification/tree/master)
Provides a mailer object and a default set of templates for sending email
notifications when errors occur in a Rails application.
* [Better Errors](https://github.com/charliesome/better_errors) Replaces the
standard Rails error page with a new one containing more contextual information,
like source code and variable inspection.
* [RailsPanel](https://github.com/dejan/rails_panel) Chrome extension for Rails
development that will end your tailing of development.log. Have all information
about your Rails app requests in the browser - in the Developer Tools panel.
Provides insight to db/rendering/total times, parameter list, rendered views and
more.
References
----------
* [ruby-debug Homepage](http://bashdb.sourceforge.net/ruby-debug/home-page.html)
* [debugger Homepage](https://github.com/cldwalker/debugger)
* [byebug Homepage](https://github.com/deivid-rodriguez/byebug)
* [Article: Debugging a Rails application with ruby-debug](http://www.sitepoint.com/debug-rails-app-ruby-debug/)
* [Ryan Bates' debugging ruby (revised) screencast](http://railscasts.com/episodes/54-debugging-ruby-revised)
* [Ryan Bates' stack trace screencast](http://railscasts.com/episodes/24-the-stack-trace)