cache: Use configuration's hash value to validate cache

Previously we use the file time stamp to judge if a cache is valid.
Here this commit introduce a new method, which calculates the total
hash value for a certain configuration's key/value paris, and tag
it into cache filename, for example, bb_cache.dat.xxxyyyzzz.

This mechanism also ensures the cache's correctness if user
dynamically setting variables from some frontend GUI, like HOB.

(Bitbake rev: 1c1df03a6c4717bfd5faab144c4f8bbfcbae0b57)

Signed-off-by: Dongxiao Xu <dongxiao.xu@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/cooker.py

@@ -849,6 +849,7 @@ class BBCooker:
         bb.event.fire(bb.event.ConfigParsed(), data)
         bb.parse.init_parser(data)
         self.configuration.data = data
+        self.configuration.data_hash = data.get_hash()
 
     def handleCollections( self, collections ):
         """Handle collections"""
@@ -1494,6 +1495,7 @@ class CookerParser(object):
         self.filelist = filelist
         self.cooker = cooker
         self.cfgdata = cooker.configuration.data
+        self.cfghash = cooker.configuration.data_hash
 
         # Accounting statistics
         self.parsed = 0
@@ -1509,7 +1511,7 @@ class CookerParser(object):
         self.num_processes = int(self.cfgdata.getVar("BB_NUMBER_PARSE_THREADS", True) or
                                  multiprocessing.cpu_count())
 
-        self.bb_cache = bb.cache.Cache(self.cfgdata, cooker.caches_array)
+        self.bb_cache = bb.cache.Cache(self.cfgdata, self.cfghash, cooker.caches_array)
         self.fromcache = []
         self.willparse = []
         for filename in self.filelist: