bitbake: cache: Add SimpleCache class

This adds a simple version of the MultiProcessCache which can be used to
save and load cache data, useful for a new usecase we have in
sigdata/runqueue.

(Bitbake rev: 19a6e35600ae6d2d1bcecca6e68ab8c37674774e)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/cache.py

@@ -883,3 +883,56 @@ class MultiProcessCache(object):
             p.dump([data, self.__class__.CACHE_VERSION])
 
         bb.utils.unlockfile(glf)
+
+
+class SimpleCache(object):
+    """
+    BitBake multi-process cache implementation
+
+    Used by the codeparser & file checksum caches
+    """
+
+    def __init__(self, version):
+        self.cachefile = None
+        self.cachedata = None
+        self.cacheversion = version
+
+    def init_cache(self, d, cache_file_name=None, defaultdata=None):
+        cachedir = (d.getVar("PERSISTENT_DIR") or
+                    d.getVar("CACHE"))
+        if not cachedir:
+            return defaultdata
+
+        bb.utils.mkdirhier(cachedir)
+        self.cachefile = os.path.join(cachedir,
+                                      cache_file_name or self.__class__.cache_file_name)
+        logger.debug(1, "Using cache in '%s'", self.cachefile)
+
+        glf = bb.utils.lockfile(self.cachefile + ".lock")
+
+        try:
+            with open(self.cachefile, "rb") as f:
+                p = pickle.Unpickler(f)
+                data, version = p.load()
+        except:
+            bb.utils.unlockfile(glf)
+            return defaultdata
+
+        bb.utils.unlockfile(glf)
+
+        if version != self.cacheversion:
+            return defaultdata
+
+        return data
+
+    def save(self, data):
+        if not self.cachefile:
+            return
+
+        glf = bb.utils.lockfile(self.cachefile + ".lock")
+
+        with open(self.cachefile, "wb") as f:
+            p = pickle.Pickler(f, -1)
+            p.dump([data, self.cacheversion])
+
+        bb.utils.unlockfile(glf)