utils.py

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#!/usr/bin/env python
#
# LSST Data Management System
#
# Copyright 2016  AURA/LSST.
#
# This product includes software developed by the
# LSST Project (http://www.lsst.org/).
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the LSST License Statement and
# the GNU General Public License along with this program.  If not,
# see <https://www.lsstcorp.org/LegalNotices/>.
#
 
__all__ = [
    "traceSetAt",
    "temporaryLogLevel",
    "LogRedirect",
    "enable_notebook_logging",
    "disable_notebook_logging",
]
 
from contextlib import contextmanager
import os
import sys
import threading
 
from lsst.log import Log
 
 
def traceSetAt(name, number):
    """Adjusts logging level to display messages with the trace number being
    less than or equal to the provided value.
 
    Parameters
    ----------
    name : `str`
        Name of the logger.
    number : `int`
        The trace number threshold for display.
    """
    for i in range(6):
        level = Log.INFO if i > number else Log.DEBUG
        Log.getLogger('TRACE%d.%s' % (i, name)).setLevel(level)
 
 
@contextmanager
def temporaryLogLevel(name, level):
    """A context manager that temporarily sets the level of a `Log`.
 
    Parameters
    ----------
    name : `str`
        Name of the log to modify.
    level : `int`
        Integer enumeration constant indicating the temporary log level.
    """
    log = Log.getLogger(name)
    old = log.getLevel()
    log.setLevel(level)
    try:
        yield
    finally:
        log.setLevel(old)
 
 
class LogRedirect:
    """Redirect a logging file descriptor to a Python stream.
 
    Parameters
    ----------
    fd : `int`
        File descriptor number, usually 1 for standard out, the default log
        output location.
    dest : `io.TextIOBase`
        Destination text stream, often `sys.stderr` for ipython or Jupyter
        notebooks.
    encoding : `str`
        Text encoding of the data written to fd.
    errors : `str`
        Encoding error handling.
 
    Notes
    -----
    Inspired by `this Stack Overflow answer
    <https://stackoverflow.com/questions/41216215>`_
    """
 
    def __init__(self, fd=1, dest=sys.stderr, encoding="utf-8", errors="strict"):
        self._fd_fd = fd
        self._dest_dest = dest
        # Save original filehandle so we can restore it later.
        self._filehandle_filehandle = os.dup(fd)
 
        # Redirect `fd` to the write end of the pipe.
        pipe_read, pipe_write = os.pipe()
        os.dup2(pipe_write, fd)
        os.close(pipe_write)
 
        # This thread reads from the read end of the pipe.
        def consumer_thread(f, data):
            while True:
                buf = os.read(f, 1024)
                if not buf:
                    break
                data.write(buf.decode(encoding, errors))
            os.close(f)
            return
 
        # Spawn consumer thread with the desired destination stream.
        self._thread_thread = threading.Thread(target=consumer_thread, args=(pipe_read, dest))
        self._thread_thread.start()
 
    def finish(self):
        """Stop redirecting output.
        """
 
        # Cleanup: flush streams, restore `fd`
        self._dest_dest.flush()
        # This dup2 closes the saved file descriptor, which is now the write
        # end of the pipe, causing the thread's read to terminate
        os.dup2(self._filehandle_filehandle, self._fd_fd)
        os.close(self._filehandle_filehandle)
        self._thread_thread.join()
 
 
_redirect = None
 
 
def enable_notebook_logging(dest=sys.stderr):
    """Enable notebook output for log4cxx messages."""
    global _redirect
    if _redirect is None:
        _redirect = LogRedirect(dest=dest)
 
 
def disable_notebook_logging():
    """Stop notebook output for log4cxx messages."""
    global _redirect
    if _redirect is not None:
        _redirect.finish()
        _redirect = None