# `mix profile.cprof`
[🔗](https://github.com/elixir-lang/elixir/blob/7ff272706afc522e74121493b7166719985cb099/lib/mix/lib/mix/tasks/profile.cprof.ex#L5)

Profiles the given file or expression using Erlang's `cprof` tool.

[`:cprof`](`:cprof`) can be useful when you want to discover the bottlenecks related
to function calls.

Before running the code, it invokes the `app.start` task which compiles
and loads your project. After that, the target expression is profiled together
with all matching function calls, by setting breakpoints containing
counters. These can only be set on BEAM code so BIFs cannot be call
count traced.

To profile the code, you can use syntax similar to the `mix run` task:

    $ mix profile.cprof -e Hello.world
    $ mix profile.cprof -e "[1, 2, 3] |> Enum.reverse |> Enum.map(&Integer.to_string/1)"
    $ mix profile.cprof my_script.exs arg1 arg2 arg3

This task is automatically re-enabled, so you can profile multiple times
in the same Mix invocation.

## Command line options

  * `--matching` - only profile calls matching the given `Module.function/arity` pattern
  * `--limit` - filters out any results with a call count less than the limit
  * `--module` - filters out any results not pertaining to the given module
  * `--eval`, `-e` - evaluate the given code
  * `--require`, `-r` - requires pattern before running the command
  * `--parallel`, `-p` - makes all requires parallel
  * `--no-compile` - does not compile even if files require compilation
  * `--no-deps-check` - does not check dependencies
  * `--no-archives-check` - does not check archives
  * `--no-halt` - does not halt the system after running the command
  * `--no-start` - does not start applications after compilation
  * `--no-elixir-version-check` - does not check the Elixir version from mix.exs

## Profile output

Example output:
                                                                         CNT
    Total                                                                 15
    Enum                                                                   6  <--
      Enum."-map/2-lists^map/1-0-"/2                                       4
      Enum.reverse/1                                                       1
      Enum.map/2                                                           1
    :elixir_compiler                                                       4  <--
      anonymous fn/1 in :elixir_compiler.__FILE__/1                        3
      anonymous fn/0 in :elixir_compiler.__FILE__/1                        1
    String.Chars.Integer                                                   3  <--
      String.Chars.Integer.to_string/1                                     3
    :erlang                                                                2  <--
      :erlang.trace_pattern/3                                              2
    Profile done over 20229 matching functions

The default output contains data gathered from all matching functions. The left
column structures each module and its total call count trace is presented on the right.
Each module has its count discriminated by function below. The `<--` symbol is meant to
help visualize where a new module call count begins.

The first row (Total) is the sum of all function calls. In the last row the number of
matching functions that were considered for profiling is presented.

When `--matching` option is specified, call count tracing will be started only for
the functions matching the given pattern:

    String.Chars.Integer                                                   3  <--
      String.Chars.Integer.to_string/1                                     3
    Profile done over 1 matching functions

The pattern can be a module name, such as `String` to count all calls to that module,
a call without arity, such as `String.split`, to count all calls to that function
regardless of arity, or a call with arity, such as `String.split/3`, to count all
calls to that exact module, function and arity.

## Caveats

You should be aware the profiler is stopped as soon as the code has finished running. This
may need special attention, when:  running asynchronous code as function calls which were
called before the profiler stopped will not be counted; running synchronous code as long
running computations and a profiler without a proper MFA trace pattern or filter may
lead to a result set which is difficult to comprehend.

Other caveats are the impossibility to call count trace BIFs, since breakpoints can
only be set on BEAM code; functions calls performed by `:cprof` are not traced; the
maximum size of a call counter is equal to the host machine's word size
(for example, `2_147_483_647` in a 32-bit host).

# `profile_opts`

```elixir
@type profile_opts() :: [
  matching: {module() | :_, atom() | :_, arity() | :_},
  limit: non_neg_integer(),
  module: module()
]
```

Options for the cprof profiler.

# `profile`

```elixir
@spec profile((-&gt; result), profile_opts()) :: result when result: any()
```

Allows to programmatically run the `cprof` profiler on expression in `fun`.

Returns the return value of `fun`.

## Options

  * `:matching` - only profile calls matching the given pattern in form of
    `{module, function, arity}`, where each element may be replaced by `:_`
    to allow any value
  * `:limit` - filters out any results with a call count less than the limit
  * `:module` - filters out any results not pertaining to the given module

---

*Consult [api-reference.md](api-reference.md) for complete listing*