- parallel module finally does something

git-svn-id: http://galileo.dmi.unict.it/svn/relational/trunk@264 014f5005-505e-4b48-8d0a-63407b615a7c

CHANGELOG

@@ -9,6 +9,7 @@
 - Fixed python expression tokenization, now uses native tokenizer
 - Fixed optimization involving selection and parenthesis in the expression (Rev 260)
 - Fixed futile_union_intersection_subtraction optimization that didn't work when selection operator was in the left subtree (Rev 261)
+- Module parallel does something, can execute queries in parallel
 
 0.11
 - Font is set only on windows (Rev 206)

relational/parallel.py

@@ -20,19 +20,92 @@
 '''This module offers capability of executing relational queries in parallel.'''
 
 import optimizer
+import multiprocessing
+import parser
 
-def weight (n,rels):
-    '''This function returns a weight that tries to give an approssimation of the
-    time that will be required to execute the expression'''
-    if n.kind==optimizer.RELATION: #Weight of a relation is its size
-        r=rels[n.name]
-        return len(r.content) * len(r.header.attributes)
-    elif n.kind==optimizer.BINARY and n.name=='ρ':
-        pass
-    elif n.kind==optimizer.BINARY and n.name=='σ':
-        pass
-    elif n.kind==optimizer.BINARY and n.name=='π':
-        pass
+def execute(tree,rels):
+    '''This funcion executes a query in parallel.
+    Tree is the tree describing the query (usually obtained with
+    parser.tree(querystring)
+    rels is a dictionary containing the relations associated with the names'''
+
+    q = multiprocessing.Queue()
+    p = multiprocessing.Process(target=__p_exec__, args=(tree,rels,q,))
+    p.start()
+    result= q.get()
+    p.join()
+    return result
+
+def __p_exec__(tree,rels,q):
+    '''q is the queue used for communication'''
+    if tree.kind==parser.RELATION:
+        q.put(rels[tree.name])
+    elif tree.kind==parser.UNARY:
+        
+        #Obtain the relation
+        temp_q = multiprocessing.Queue()
+        __p_exec__(tree.child,rels,temp_q)
+        rel=temp_q.get()
+        
+        #Execute the query
+        result=__p_exec_unary__(tree,rel)
+        q.put(result)
+    elif tree.kind==parser.BINARY:
+        left_q = multiprocessing.Queue()
+        left_p = multiprocessing.Process(target=__p_exec__, args=(tree.left,rels,left_q,))
+        right_q = multiprocessing.Queue()
+        right_p = multiprocessing.Process(target=__p_exec__, args=(tree.right,rels,right_q,))
         
         
-    pass
+        #Spawn the children
+        left_p.start()
+        right_p.start()
+                
+        #Get the left and right relations
+        left= left_q.get()
+        right= right_q.get()
+        
+        #Wait for the children to terminate
+        left_p.join()
+        right_p.join()
+        
+        result = __p_exec_binary__(tree,left,right)
+        q.put(result)
+    return
+def __p_exec_binary__(tree,left,right):
+    if tree.name=='*':
+        return left.product(right)
+    elif tree.name=='-':
+        return left.difference(right)
+    elif tree.name=='ᑌ':
+        return left.union(right)
+    elif tree.name=='ᑎ':
+        return left.intersection(right)
+    elif tree.name=='÷':
+        return left.division(right)
+    elif tree.name=='ᐅᐊ':
+        return left.join(right)
+    elif tree.name=='ᐅLEFTᐊ':
+        return left.outer_left(right)
+    elif tree.name=='ᐅRIGHTᐊ':
+        return left.outer_right(right)
+    else: # tree.name=='ᐅFULLᐊ':
+        return left.outer(right)
+    
+def __p_exec_unary__(tree,rel):
+    if tree.name=='π':#Projection
+        tree.prop=tree.prop.replace(' ','').split(',')
+        result= rel.projection(tree.prop)
+    elif tree.name=="ρ": #Rename
+        #tree.prop='{\"%s\"}' % tree.prop.replace(',','\",\"').replace('➡','\":\"').replace(' ','')
+        d={}
+        tree.prop=tree.prop.replace(' ','')
+        for i in tree.prop.split(','):
+            rename_=i.split('➡')
+            d[rename_[0]]=rename_[1]
+        
+        result= rel.rename(d)
+    else: #Selection
+        result= rel.selection(tree.prop)       
+    return result
+