code release

xlib/mp/RWLock.py

@@ -0,0 +1,83 @@
+import multiprocessing
+
+class RWLock():
+    """
+    Multiprocessing non-recursive reader-writer lock
+    """
+    def __init__(self):
+        self._a = multiprocessing.RawArray('I', 2)
+        #_a[0] : readers counter
+        #_a[1] : writer flag
+        self._v = memoryview(self._a).cast('B').cast('I')
+        self._l = multiprocessing.Lock()
+
+    def read_lock(self):
+        v = self._v
+        l = self._l
+        while True:
+            # Non blocky wait writer flag release
+            while v[1] != 0:
+                pass
+
+            l.acquire()
+            if v[1] != 0:
+                # Writer flag is still acquired, go to non-blocky waiting
+                l.release()
+                continue
+
+            # Inc readers counter
+            v[0] += 1
+            l.release()
+            return
+
+    def read_unlock(self):
+        v = self._v
+        l = self._l
+        l.acquire()
+        c = v[0]
+        if c == 0:
+            raise Exception('Invalid lock state')
+        # Dec readers counter
+        v[0] = c-1
+        l.release()
+
+    def write_lock(self):
+        v = self._v
+        l = self._l
+
+        while True:
+            # Non blocky wait writer flag release
+            while v[1] != 0:
+                pass
+            l.acquire()
+            if v[1] != 0:
+                # Writer flag is still acquired, go to non-blocky waiting
+                l.release()
+                continue
+            # set writer flag
+            v[1] = 1
+            l.release()
+
+            # Wait all readers gone
+            while v[0] != 0:
+                pass
+            return
+
+    def write_unlock(self):
+        v = self._v
+        c = v[1]
+        if c == 0:
+            raise Exception('Invalid lock state')
+        # Remove writer flag
+        v[1] = 0
+
+    def __getstate__(self):
+        d = self.__dict__.copy()
+        # pop unpicklable memoryview object
+        d.pop('_v')
+        return d
+
+    def __setstate__(self, d):
+        # restore memoryview of RawArray
+        d['_v'] = memoryview(d['_a']).cast('B').cast('I')
+        self.__dict__.update(d)