multiemitter.py

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#!/usr/bin/env python3
# Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
# for details. All rights reserved. Use of this source code is governed by a
# BSD-style license that can be found in the LICENSE file.
"""Templating to help generate structured text."""
 
import os
import sys
import subprocess
import time
import emitter
import logging
 
_logger = logging.getLogger('multiemitter')
 
 
class MultiEmitter(object):
    """A set of Emitters that write to different files.
 
  Each entry has a key.
 
  file --> emitter
  key --> emitter
 
  """
 
    def __init__(self, logging_level=logging.WARNING):
        self._key_to_emitter = {}  # key -> Emitter
        self._filename_to_emitter = {}  # filename -> Emitter
 
        _logger.setLevel(logging_level)
 
    def FileEmitter(self, filename, key=None):
        """Creates an emitter for writing to a file.
 
    When this MultiEmitter is flushed, the contents of the emitter are written
    to the file.
 
    Arguments:
      filename: a string, the path name of the file
      key: provides an access key to retrieve the emitter.
 
    Returns: the emitter.
    """
        e = emitter.Emitter()
        self._filename_to_emitter[filename] = e
        if key:
            self.Associate(key, e)
        return e
 
    def Associate(self, key, emitter):
        """Associates a key with an emitter."""
        self._key_to_emitter[key] = emitter
 
    def Find(self, key):
        """Returns the emitter associated with |key|."""
        return self._key_to_emitter[key]
 
    def Flush(self, writer=None):
        """Writes all pending files.
 
    Arguments:
      writer: a function called for each file and it's lines.
    """
        if not writer:
            writer = _WriteFile
        for file in sorted(self._filename_to_emitter.keys()):
            emitter = self._filename_to_emitter[file]
            writer(file, emitter.Fragments())
 
 
def _WriteFile(path, lines):
    (dir, file) = os.path.split(path)
 
    # Ensure dir exists.
    if dir:
        if not os.path.isdir(dir):
            _logger.info('Mkdir - %s' % dir)
            os.makedirs(dir)
 
    # If file exists and is unchanged, return.
    new_contents = ''.join(lines)
    if os.path.exists(path):
        with open(path) as fd:
            contents = fd.read()
        if new_contents == contents:
            _logger.info('Unchanged file %s' % path)
            return
 
    # Write the file.
    num_attempts = 4
    for i in range(num_attempts):
        try:
            _logger.info('Writing (attempt %d) - %s' % (i + 1, path))
            with open(path, 'w') as fd:
                fd.write(new_contents)
            return
        except IOError as error:
            last_attempt = (i == (num_attempts - 1))
            if not last_attempt:
                # Sleep for 50 ms and try again
                time.sleep(0.05)
            else:
                _logger.info('Got exception (%s) ' % error)
                raise error