Metadata-Version: 2.1
Name: py-spy
Version: 0.2.0.dev3
Summary: A Sampling Profiler for Python
Home-page: https://github.com/benfred/py-spy
Author: Ben Frederickson
Author-email: ben@benfrederickson.com
License: GPL
Platform: UNKNOWN
Classifier: Development Status :: 3 - Alpha
Classifier: Programming Language :: Python :: 3
Classifier: Programming Language :: Python :: 2
Classifier: Intended Audience :: Developers
Classifier: License :: OSI Approved :: GNU General Public License v3 (GPLv3)
Classifier: Topic :: Software Development :: Libraries
Classifier: Topic :: Utilities

py-spy: A sampling profiler for Python programs.
================================================

|Build Status| |Windows Build status|

py-spy is a sampling profiler for Python programs. It lets you visualize
what your Python program is spending time on without restarting the
program or modifying the code in any way. py-spy is extremely low
overhead: it is written in Rust for speed and doesn't run in the same
process as the profiled Python program. This means py-spy is safe to use
against production Python code.

py-spy works on Linux, OSX and Windows, and supports profiling all
recent versions of the CPython interpreter (versions 2.3-2.7 and
3.3-3.7).

Installation
------------

Prebuilt binary wheels can be installed from PyPI with:

::

    pip install py-spy

If you're a Rust user, py-spy can also be installed with:

::

    cargo install py-spy

On Arch Linux, `py-spy is in
AUR <https://aur.archlinux.org/packages/py-spy/>`__ and can be installed
by using your favorite AUR helper, for example:

::

    yay -S py-spy

Usage
-----

py-spy works from the command line and takes either the PID of the
program you want to sample from or the command line of the python
program you want to run:

.. code:: bash

    py-spy --pid 12345
    # OR
    py-spy -- python myprogram.py

The default visualization is a
`top-like <https://linux.die.net/man/1/top>`__ live view of your python
program:

.. figure:: ./images/console_viewer.gif
   :alt: console viewer demo

   console viewer demo

There is also support for generating `flame
graphs <http://www.brendangregg.com/flamegraphs.html>`__ from the
running process:

.. code:: bash

    py-spy --flame profile.svg --pid 12345
    # OR
    py-spy --flame profile.svg -- python myprogram.py

Which will generate a SVG file looking like:

.. figure:: ./images/flamegraph.svg
   :alt: flame graph

   flame graph

It also possible to dump out the current call stack for each thread by
passing ``--dump`` to the command line.

Frequently Asked Questions
--------------------------

Why do we need another Python profiler?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This project aims to let you profile and debug any running Python
program, even if the program is serving production traffic.

While there are many other python profiling projects, almost all of them
require modifying the profiled program in some way. Usually, the
profiling code runs inside of the target python process, which will slow
down and change how the program operates. This means it's not generally
safe to use these profilers for debugging issues in production services
since they will usually have a noticeable impact on performance. The
only other Python profiler that runs totally in a separate process is
`pyflame <https://github.com/uber/pyflame>`__, which profiles remote
python processes by using the ptrace system call. While pyflame is a
great project, it doesn't support Python 3.7 yet and doesn't work on OSX
or Windows.

How does py-spy work?
~~~~~~~~~~~~~~~~~~~~~

py-spy works by directly reading the memory of the python program using
the
`process\_vm\_readv <http://man7.org/linux/man-pages/man2/process_vm_readv.2.html>`__
system call on Linux, the
`vm\_read <https://developer.apple.com/documentation/kernel/1585350-vm_read?language=objc>`__
call on OSX or the
`ReadProcessMemory <https://msdn.microsoft.com/en-us/library/windows/desktop/ms680553(v=vs.85).aspx>`__
call on Windows.

Figuring out the call stack of the Python program is done by looking at
the global PyInterpreterState variable to get all the Python threads
running in the interpreter, and then iterating over each PyFrameObject
in each thread to get the call stack. Since the Python ABI changes
between versions, we use rust's
`bindgen <https://github.com/rust-lang-nursery/rust-bindgen>`__ to
generate different rust structures for each Python interpreter class we
care about and use these generated structs to figure out the memory
layout in the Python program.

Getting the memory address of the Python Interpreter can be a little
tricky due to `Address Space Layout
Randomization <https://en.wikipedia.org/wiki/Address_space_layout_randomization>`__.
If the target python interpreter ships with symbols it is pretty easy to
figure out the memory address of the interpreter by dereferencing the
``interp_head`` or ``_PyRuntime`` variables depending on the Python
version. However, many Python versions are shipped with either stripped
binaries or shipped without the corresponding PDB symbol files on
Windows. In these cases we scan through the BSS section for addresses
that look like they may point to a valid PyInterpreterState and check if
the layout of that address is what we expect.

Can py-spy profile native extensions?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Since we're getting the call stacks of the python program by looking at
the
`PyInterpreterState <https://docs.python.org/3/c-api/init.html#c.PyInterpreterState>`__
we don't yet get information about non-python threads and can't profile
native extensions like those written in languages like Cython or C++.
Native code will instead show up as spending time in the line of Python
that calls the native function, rather than as its own entry right now.

It should be possible to use something like
`libunwind <https://www.nongnu.org/libunwind/>`__ to profile the native
code in the Python Extensions. If this is something that interests you
`please upvote this
issue <https://github.com/benfred/py-spy/issues/2>`__.

When do you need to run as sudo?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

py-spy works by reading memory from a different python process, and this
might not be allowed for security reasons depending on your OS and
system settings. In many cases, running as a root user (with sudo or
similar) gets around these security restrictions. OSX always requires
running as root, but on Linux it depends on how you are launching py-spy
and the system security settings.

On Linux the default configuration is to require root permissions when
attaching to a process that isn't a child. For py-spy this means you can
profile without root access by getting py-spy to create the process
(``py-spy -- python myprogram.py``) but attaching to an existing process
by specifying a PID will usually require root
(``sudo py-spy --pid 123456``). You can remove this restriction on linux
by setting the `ptrace\_scope sysctl
variable <https://wiki.ubuntu.com/SecurityTeam/Roadmap/KernelHardening#ptrace_Protection>`__.

Why am I having issues profiling /usr/bin/python on OSX?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

OSX has a feature called `System Integrity
Protection <https://en.wikipedia.org/wiki/System_Integrity_Protection>`__
that prevents even the root user from reading memory from any binary
located in /usr/bin. Unfortunately, this includes the python interpreter
that ships with OSX.

There are a couple of different ways to deal with this: \* You can
install a different Python distribution (you probably want to migrate
away from python2 anyways =) \* You can use
`virtualenv <https://virtualenv.pypa.io/en/stable/>`__ to run the system
python in an environment where SIP doesn't apply. \* You can `disable
System Integrity
Protection <https://www.macworld.co.uk/how-to/mac/how-turn-off-mac-os-x-system-integrity-protection-rootless-3638975/>`__.

How do I run py-spy in Docker?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Running py-spy inside of a docker container will also usually bring up a
permissions denied error even when running as root.

This error is caused by docker restricting the process\_vm\_readv system
call we are using. This can be overridden by setting
```--cap-add SYS_PTRACE`` <https://docs.docker.com/engine/security/seccomp/>`__
when starting the docker container.

Alternatively you can edit the docker-compose yaml file

::

    your_service:
       cap_add:
         - SYS_PTRACE

Note that you'll need to restart the docker container in order for this
setting to take effect.

How do I run py-spy in Kubernetes?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

py-spy needs ``SYS_PTRACE`` to be able to read process memory.
Kubernetes drops that capability by default, resulting in the error

::

    Permission Denied: Try running again with elevated permissions by going 'sudo env "PATH=$PATH" !!'

The recommended way to deal with this is to edit the spec and add that
capability. For a deployment, this is done by adding this to
``Deployment.spec.template.spec.containers``

::

    securityContext:
      capabilities:
        add:
        - SYS_PTRACE

More details on this here:
https://kubernetes.io/docs/tasks/configure-pod-container/security-context/#set-capabilities-for-a-container
Note that this will remove the existing pods and create those again.

Running py-spy in Alpine Linux
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Alpine python opts out of the ``manylinux`` wheels: `pypa/pip#3969
(comment) <https://github.com/pypa/pip/issues/3969#issuecomment-247381915>`__.
Before installing py-spy on Alpine docker containers do:

::

    echo 'manylinux1_compatible = True' > /usr/local/lib/python3.7/site-packages/_manylinux.py

How can you avoid pausing the Python program?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

By setting the ``--nonblocking`` option, py-spy won't pause the target
python you are profiling from. While the performance impact of sampling
from a process with py-spy is usually extremely low, setting this option
will totally avoid interrupting your running python program.

With this option set, py-spy will instead read the interpreter state
from the python process as it is running. Since the calls we use to read
memory from are not atomic, and we have to issue multiple calls to get a
stack trace this means that occasionally we get errors when sampling.
This can show up as an increased error rate when sampling, or as partial
stack frames being included in the output.

How are you distributing Rust executable binaries over PyPI?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Ok, so no-one has ever actually asked me this - but I wanted to share
since it's a pretty terrible hack that might be useful to other people.

I really wanted to distribute this package over PyPI, since installing
with pip will make this much easier for most Python programmers to get
installed on their system. Unfortunately, `installing executables as
python scripts isn't something that setuptools
supports <https://github.com/pypa/setuptools/issues/210>`__.

To get around this I'm using setuptools\_rust package to build the
py-spy binary, and then overriding the `distutils install
command <https://github.com/benfred/py-spy/blob/master/setup.py#L20>`__
to copy the built binary into the python scripts folder. By doing this
with prebuilt wheels for supported platforms means that we can install
py-spy with pip, and not require a Rust compiler on the machine that
this is being installed onto.

Does this run on BSD? Support 32-bit Windows? Integrate with PyPy? Work with USC-16 versions of Python2?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Not yet =).

Credits
-------

py-spy is heavily inspired by `Julia Evans <https://github.com/jvns/>`__
excellent work on `rbspy <http://github.com/rbspy/rbspy>`__. In
particular, the code to generate the flamegraphs is taken directly from
rbspy, and this project uses the
`read-process-memory <https://github.com/luser/read-process-memory>`__
and `proc-maps <https://github.com/benfred/proc-maps>`__ crates that
were spun off from rbspy.

License
-------

Py-spy is released under the GNU General Public License v3.0, see the
`LICENSE <https://github.com/benfred/py-spy/blob/master/LICENSE>`__ file
for the full text.

.. |Build Status| image:: https://travis-ci.org/benfred/py-spy.svg?branch=master
   :target: https://travis-ci.org/benfred/py-spy
.. |Windows Build status| image:: https://ci.appveyor.com/api/projects/status/x0jwd5ygaybsa0md?svg=true
   :target: https://ci.appveyor.com/project/benfred/py-spy


