energymon 0.1.2

Python bindings to native energymon libraries

EnergyMon Python Bindings

This project provides Python bindings to energymon libraries.

If using this project for other scientific works or publications, please reference:

• Connor Imes, Lars Bergstrom, and Henry Hoffmann. "A Portable Interface for Runtime Energy Monitoring". In: FSE. 2016. DOI: https://doi.org/10.1145/2950290.2983956

  [BibTex]

  @inproceedings{imes2016energymon,
    author = {Imes, Connor and Bergstrom, Lars and Hoffmann, Henry},
    title = {A Portable Interface for Runtime Energy Monitoring},
    year = {2016},
    isbn = {9781450342186},
    publisher = {Association for Computing Machinery},
    address = {New York, NY, USA},
    url = {https://doi.org/10.1145/2950290.2983956},
    doi = {10.1145/2950290.2983956},
    booktitle = {Proceedings of the 2016 24th ACM SIGSOFT International Symposium on Foundations of Software Engineering},
    pages = {968–974},
    numpages = {7},
    keywords = {portable energy measurement},
    location = {Seattle, WA, USA},
    series = {FSE 2016}
  }
  

Dependencies

The energymon libraries should be installed to the system and on the library search path (e.g., LD_LIBRARY_PATH on Linux/POSIX systems or DYLD_LIBRARY_PATH on macOS systems).

The latest energymon C libraries can be found at https://github.com/energymon/energymon.

Installing

Versioned releases of the energymon package are published in the Python Package Index and installable with pip:

pip install energymon

and through Conda Forge:

conda install energymon

To install from source:

pip install .

Usage

The following subsections document usage with increasing levels of abstraction.

Direct Bindings

At the lowest level, the energymon package exposes an energymon class, which is a binding to the energymon C struct.

To directly use the energymon API, first load the library, create and "get" the struct to populate its function pointers, then initialize, do work, and cleanup when finished. For example:

from ctypes import CDLL, byref, create_string_buffer, sizeof, set_errno, get_errno
from ctypes.util import find_library
from energymon import energymon

# try to find the library by name:
lib_path = find_library('energymon-default')
if lib_path is None:
    # maybe fall back on a relative or absolute path
    lib_path = 'libenergymon-default.so'

lib = CDLL(lib_path, use_errno=True)
em = energymon()
if lib.energymon_get_default(byref(em)) != 0:
    # handle error...
    exit(1)

name = create_string_buffer(256)
if not em.fsource(name, sizeof(name)):
    # handle error
    exit(1)

print(name.value.decode())
if em.finit(byref(em)) != 0:
    # handle error
    exit(1)

set_errno(0)
uj = em.fread(byref(em))
if uj == 0 and get_errno() != 0:
    # handle error (but don't skip cleanup!)
    pass

if em.ffinish(byref(em)) != 0:
    # handle error
    exit(1)

Utility Functions

Utility functions work with the direct bindings, but simplify their usage by (1) abstracting the user from the Python ctypes (including pointers) and (2) raising exceptions when errors are reported by the native library. For example, to load the energymon-default library, "get" the energymon, and report the energy source and current value:

from energymon import util

lib = util.load_energymon_library()
em = util.get_energymon(lib)
print(util.get_source(em))
util.init(em)
try:
    print(util.get_uj(em))
finally:
    util.finish(em)

Context Management

The context submodule provides the EnergyMon class, which is both a wrapper around energymon bindings and a Python context manager. As a context manager, the class handles the energymon lifecycle, and is both reentrant and reusable. For example, to use as a context manager:

from energymon.context import EnergyMon

with EnergyMon() as em:
    print('source:', em.get_source())
    print('reading (uJ):', em.get_uj())

Alternatively, you can manage the lifecycle yourself with em.init() and em.finish() (instead of using with ...). Take care to handle exceptions, including correct lifecycle management if not using the automatic context management.

Project Source

Find this and related project sources at the energymon organization on GitHub.
This project originates at: https://github.com/energymon/energymon-py

Bug reports and pull requests for bug fixes and enhancements are welcome.