1 # Copyright 2013 The Chromium Authors. All rights reserved. 2 # Use of this source code is governed by a BSD-style license that can be 3 # found in the LICENSE file. 4 5 from compiled_file_system import CompiledFileSystem 6 from docs_server_utils import StringIdentity 7 from file_system import FileNotFoundError 8 from future import Future 9 10 11 class ChainedCompiledFileSystem(object): 12 '''A CompiledFileSystem implementation that fetches data from a chain of 13 possible FileSystems. The chain consists of some number of FileSystems which 14 may have cached data for their CompiledFileSystem instances (injected on 15 Factory construction) + the main FileSystem (injected at Creation time). 16 17 The expected configuration is that the main FileSystem is a PatchedFileSystem 18 and the chain the FileSystem which it patches, but with file systems 19 constructed via the HostFileSystemIterator the main FileSystems could be 20 anything. 21 22 This slightly unusual configuration is primarily needed to avoid re-compiling 23 data for PatchedFileSystems, which are very similar to the FileSystem which 24 they patch. Re-compiling data is expensive and a waste of memory resources. 25 ChainedCompiledFileSystem shares the data. 26 ''' 27 class Factory(CompiledFileSystem.Factory): 28 def __init__(self, file_system_chain, object_store): 29 self._file_system_chain = file_system_chain 30 self._object_store = object_store 31 32 def Create(self, file_system, populate_function, cls, category=None): 33 return ChainedCompiledFileSystem( 34 # Chain of CompiledFileSystem instances. 35 tuple(CompiledFileSystem.Factory(self._object_store).Create( 36 fs, populate_function, cls, category=category) 37 for fs in [file_system] + self._file_system_chain), 38 # Identity, as computed by all file systems. 39 StringIdentity(*(fs.GetIdentity() for fs in self._file_system_chain))) 40 41 def __init__(self, compiled_fs_chain, identity): 42 '''|compiled_fs_chain| is a list of tuples (compiled_fs, file_system). 43 ''' 44 assert len(compiled_fs_chain) > 0 45 self._compiled_fs_chain = compiled_fs_chain 46 self._identity = identity 47 48 def GetFromFile(self, path): 49 return self._GetImpl( 50 path, 51 lambda compiled_fs: compiled_fs.GetFromFile(path), 52 lambda compiled_fs: compiled_fs.GetFileVersion(path)) 53 54 def GetFromFileListing(self, path): 55 if not path.endswith('/'): 56 path += '/' 57 return self._GetImpl( 58 path, 59 lambda compiled_fs: compiled_fs.GetFromFileListing(path), 60 lambda compiled_fs: compiled_fs.GetFileListingVersion(path)) 61 62 def _GetImpl(self, path, reader, version_getter): 63 # Strategy: Get the current version of |path| in main FileSystem, then run 64 # through |_compiled_fs_chain| in *reverse* to find the "oldest" FileSystem 65 # with an up-to-date version of that file. 66 # 67 # Obviously, if files have been added in the main FileSystem then none of 68 # the older FileSystems will be able to find it. 69 read_futures = [(reader(compiled_fs), compiled_fs) 70 for compiled_fs in self._compiled_fs_chain] 71 72 def resolve(): 73 try: 74 first_compiled_fs = self._compiled_fs_chain[0] 75 # The first file system contains both files of a newer version and 76 # files shared with other compiled file systems. We are going to try 77 # each compiled file system in the reverse order and return the data 78 # when version matches. Data cached in other compiled file system will 79 # be reused whenever possible so that we don't need to recompile things 80 # that are not changed across these file systems. 81 first_version = version_getter(first_compiled_fs) 82 for read_future, compiled_fs in reversed(read_futures): 83 if version_getter(compiled_fs) == first_version: 84 return read_future.Get() 85 except FileNotFoundError: 86 pass 87 # Try an arbitrary operation again to generate a realistic stack trace. 88 return read_futures[0][0].Get() 89 90 return Future(callback=resolve) 91 92 def GetIdentity(self): 93 return self._identity 94
