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 5from compiled_file_system import CompiledFileSystem 6from docs_server_utils import StringIdentity 7from file_system import FileNotFoundError 8from future import Future 9from path_util import ToDirectory 10 11 12class ChainedCompiledFileSystem(object): 13 '''A CompiledFileSystem implementation that fetches data from a chain of 14 possible FileSystems. The chain consists of some number of FileSystems which 15 may have cached data for their CompiledFileSystem instances (injected on 16 Factory construction) + the main FileSystem (injected at Creation time). 17 18 The expected configuration is that the main FileSystem is a PatchedFileSystem 19 and the chain the FileSystem which it patches, but with file systems 20 constructed via the HostFileSystemIterator the main FileSystems could be 21 anything. 22 23 This slightly unusual configuration is primarily needed to avoid re-compiling 24 data for PatchedFileSystems, which are very similar to the FileSystem which 25 they patch. Re-compiling data is expensive and a waste of memory resources. 26 ChainedCompiledFileSystem shares the data. 27 ''' 28 class Factory(CompiledFileSystem.Factory): 29 def __init__(self, file_system_chain, object_store): 30 self._file_system_chain = file_system_chain 31 self._object_store = object_store 32 33 def Create(self, file_system, populate_function, cls, category=None): 34 return ChainedCompiledFileSystem( 35 # Chain of CompiledFileSystem instances. 36 tuple(CompiledFileSystem.Factory(self._object_store).Create( 37 fs, populate_function, cls, category=category) 38 for fs in [file_system] + self._file_system_chain), 39 # Identity, as computed by all file systems. 40 StringIdentity(*(fs.GetIdentity() for fs in self._file_system_chain))) 41 42 def __init__(self, compiled_fs_chain, identity): 43 '''|compiled_fs_chain| is a list of tuples (compiled_fs, file_system). 44 ''' 45 assert len(compiled_fs_chain) > 0 46 self._compiled_fs_chain = compiled_fs_chain 47 self._identity = identity 48 49 def GetFromFile(self, path, skip_not_found=False): 50 return self._GetImpl( 51 path, 52 lambda cfs: cfs.GetFromFile(path, skip_not_found=skip_not_found), 53 lambda cfs: cfs._GetFileVersionFromCache(path)) 54 55 def GetFromFileListing(self, path): 56 path = ToDirectory(path) 57 return self._GetImpl( 58 path, 59 lambda compiled_fs: compiled_fs.GetFromFileListing(path), 60 lambda compiled_fs: compiled_fs._GetFileListingVersionFromCache(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_and_version_futures = [(reader(fs), version_getter(fs), fs) 70 for fs in self._compiled_fs_chain] 71 72 def resolve(): 73 try: 74 # The first file system contains both files of a newer version and 75 # files shared with other compiled file systems. We are going to try 76 # each compiled file system in the reverse order and return the data 77 # when version matches. Data cached in other compiled file system will 78 # be reused whenever possible so that we don't need to recompile things 79 # that are not changed across these file systems. 80 first_version = read_and_version_futures[0][1].Get() 81 for (read_future, 82 version_future, 83 compiled_fs) in reversed(read_and_version_futures): 84 if version_future.Get() == first_version: 85 return read_future.Get() 86 except FileNotFoundError: 87 pass 88 # Try an arbitrary operation again to generate a realistic stack trace. 89 return read_and_version_futures[0][0].Get() 90 91 return Future(callback=resolve) 92 93 def GetIdentity(self): 94 return self._identity 95