Package SCons :: Module PathList
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Source Code for Module SCons.PathList

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 23   
 24  __revision__ = "src/engine/SCons/PathList.py issue-2856:2676:d23b7a2f45e8 2012/08/05 15:38:28 garyo" 
 25   
 26  __doc__ = """SCons.PathList 
 27   
 28  A module for handling lists of directory paths (the sort of things 
 29  that get set as CPPPATH, LIBPATH, etc.) with as much caching of data and 
 30  efficiency as we can while still keeping the evaluation delayed so that we 
 31  Do the Right Thing (almost) regardless of how the variable is specified. 
 32   
 33  """ 
 34   
 35  import os 
 36   
 37  import SCons.Memoize 
 38  import SCons.Node 
 39  import SCons.Util 
 40   
 41  # 
 42  # Variables to specify the different types of entries in a PathList object: 
 43  # 
 44   
 45  TYPE_STRING_NO_SUBST = 0        # string with no '$' 
 46  TYPE_STRING_SUBST = 1           # string containing '$' 
 47  TYPE_OBJECT = 2                 # other object 
 48   
49 -def node_conv(obj):
50 """ 51 This is the "string conversion" routine that we have our substitutions 52 use to return Nodes, not strings. This relies on the fact that an 53 EntryProxy object has a get() method that returns the underlying 54 Node that it wraps, which is a bit of architectural dependence 55 that we might need to break or modify in the future in response to 56 additional requirements. 57 """ 58 try: 59 get = obj.get 60 except AttributeError: 61 if isinstance(obj, SCons.Node.Node) or SCons.Util.is_Sequence( obj ): 62 result = obj 63 else: 64 result = str(obj) 65 else: 66 result = get() 67 return result
68
69 -class _PathList(object):
70 """ 71 An actual PathList object. 72 """
73 - def __init__(self, pathlist):
74 """ 75 Initializes a PathList object, canonicalizing the input and 76 pre-processing it for quicker substitution later. 77 78 The stored representation of the PathList is a list of tuples 79 containing (type, value), where the "type" is one of the TYPE_* 80 variables defined above. We distinguish between: 81 82 strings that contain no '$' and therefore need no 83 delayed-evaluation string substitution (we expect that there 84 will be many of these and that we therefore get a pretty 85 big win from avoiding string substitution) 86 87 strings that contain '$' and therefore need substitution 88 (the hard case is things like '${TARGET.dir}/include', 89 which require re-evaluation for every target + source) 90 91 other objects (which may be something like an EntryProxy 92 that needs a method called to return a Node) 93 94 Pre-identifying the type of each element in the PathList up-front 95 and storing the type in the list of tuples is intended to reduce 96 the amount of calculation when we actually do the substitution 97 over and over for each target. 98 """ 99 if SCons.Util.is_String(pathlist): 100 pathlist = pathlist.split(os.pathsep) 101 elif not SCons.Util.is_Sequence(pathlist): 102 pathlist = [pathlist] 103 104 pl = [] 105 for p in pathlist: 106 try: 107 index = p.find('$') 108 except (AttributeError, TypeError): 109 type = TYPE_OBJECT 110 else: 111 if index == -1: 112 type = TYPE_STRING_NO_SUBST 113 else: 114 type = TYPE_STRING_SUBST 115 pl.append((type, p)) 116 117 self.pathlist = tuple(pl)
118
119 - def __len__(self): return len(self.pathlist)
120
121 - def __getitem__(self, i): return self.pathlist[i]
122
123 - def subst_path(self, env, target, source):
124 """ 125 Performs construction variable substitution on a pre-digested 126 PathList for a specific target and source. 127 """ 128 result = [] 129 for type, value in self.pathlist: 130 if type == TYPE_STRING_SUBST: 131 value = env.subst(value, target=target, source=source, 132 conv=node_conv) 133 if SCons.Util.is_Sequence(value): 134 result.extend(value) 135 continue 136 137 elif type == TYPE_OBJECT: 138 value = node_conv(value) 139 if value: 140 result.append(value) 141 return tuple(result)
142 143
144 -class PathListCache(object):
145 """ 146 A class to handle caching of PathList lookups. 147 148 This class gets instantiated once and then deleted from the namespace, 149 so it's used as a Singleton (although we don't enforce that in the 150 usual Pythonic ways). We could have just made the cache a dictionary 151 in the module namespace, but putting it in this class allows us to 152 use the same Memoizer pattern that we use elsewhere to count cache 153 hits and misses, which is very valuable. 154 155 Lookup keys in the cache are computed by the _PathList_key() method. 156 Cache lookup should be quick, so we don't spend cycles canonicalizing 157 all forms of the same lookup key. For example, 'x:y' and ['x', 158 'y'] logically represent the same list, but we don't bother to 159 split string representations and treat those two equivalently. 160 (Note, however, that we do, treat lists and tuples the same.) 161 162 The main type of duplication we're trying to catch will come from 163 looking up the same path list from two different clones of the 164 same construction environment. That is, given 165 166 env2 = env1.Clone() 167 168 both env1 and env2 will have the same CPPPATH value, and we can 169 cheaply avoid re-parsing both values of CPPPATH by using the 170 common value from this cache. 171 """ 172 if SCons.Memoize.use_memoizer: 173 __metaclass__ = SCons.Memoize.Memoized_Metaclass 174 175 memoizer_counters = [] 176
177 - def __init__(self):
178 self._memo = {}
179
180 - def _PathList_key(self, pathlist):
181 """ 182 Returns the key for memoization of PathLists. 183 184 Note that we want this to be pretty quick, so we don't completely 185 canonicalize all forms of the same list. For example, 186 'dir1:$ROOT/dir2' and ['$ROOT/dir1', 'dir'] may logically 187 represent the same list if you're executing from $ROOT, but 188 we're not going to bother splitting strings into path elements, 189 or massaging strings into Nodes, to identify that equivalence. 190 We just want to eliminate obvious redundancy from the normal 191 case of re-using exactly the same cloned value for a path. 192 """ 193 if SCons.Util.is_Sequence(pathlist): 194 pathlist = tuple(SCons.Util.flatten(pathlist)) 195 return pathlist
196 197 memoizer_counters.append(SCons.Memoize.CountDict('PathList', _PathList_key)) 198
199 - def PathList(self, pathlist):
200 """ 201 Returns the cached _PathList object for the specified pathlist, 202 creating and caching a new object as necessary. 203 """ 204 pathlist = self._PathList_key(pathlist) 205 try: 206 memo_dict = self._memo['PathList'] 207 except KeyError: 208 memo_dict = {} 209 self._memo['PathList'] = memo_dict 210 else: 211 try: 212 return memo_dict[pathlist] 213 except KeyError: 214 pass 215 216 result = _PathList(pathlist) 217 218 memo_dict[pathlist] = result 219 220 return result
221 222 PathList = PathListCache().PathList 223 224 225 del PathListCache 226 227 # Local Variables: 228 # tab-width:4 229 # indent-tabs-mode:nil 230 # End: 231 # vim: set expandtab tabstop=4 shiftwidth=4: 232