CORES==0 disable parallel

Author: Qian Wenjie

README.md

@@ -20,8 +20,9 @@ the cache mechanism of pure function call with the same parameters. By adding
 parameter "*debug=True*", it is easy to show the evaluation process step by step.
 
     >>> from lazy import Lazy
+    >>> lazy_int = Lazy(int, debug=True)
     >>> def fib(n):
-    ...     return Lazy(int, debug=True)(n) if n <= 1 else fib(n-1) + fib(n-2)
+    ...     return lazy_int(n) if n <= 1 else fib(n-1) + fib(n-2)
     ... 
     >>> a = fib(10)
     >>> a
@@ -84,7 +85,7 @@ example shows how the implicit parallel works by using decorator *lazy*.
         s.eval()
         print(s)
 
-    $ time python3 1.py
+    $ time python3 test_parallel.py
     ((f1()*f2())+(f3()*f4()))
     Enter f1
     Enter f2
@@ -98,5 +99,26 @@ example shows how the implicit parallel works by using decorator *lazy*.
 
     real    0m5.173s
     user    0m0.111s
-    sys 0m0.049s
+    sys     0m0.049s
+
+You can easily change the number of CPU cores in parallel computing by adding
+*Lazy.set_cores(num)*. You can completely disable parallel by *Lazy.set_cores(0)*.
+
+    $ time python3 test_parallel_with_zero_cores.py
+    ((f1()*f2())+(f3()*f4()))
+    Enter f2
+    Leave f2
+    Enter f1
+    Leave f1
+    Enter f3
+    Leave f3
+    Enter f4
+    Leave f4
+    14
+    
+    real    0m20.085s
+    user    0m0.055s
+    sys     0m0.016s
+
+
 

lazy/lazy.py

@@ -133,13 +133,16 @@ def startjob(self):
         Lazy.JOBS.discard(self)
         if self.remote:
             Lazy.ACTIVE += 1
-            self.POOL.apply_async(self.operator, args, callback = self.finish)
+            if Lazy.POOL:
+                Lazy.POOL.apply_async(self.operator, args, callback = self.finish)
+            else:
+                self.finish(self.operator(*args))
         else:
             self.finish(self.operator(*args))
     def eval(self):
         if self.value is not None:
             return self.value
-        if Lazy.POOL is None:
+        if Lazy.POOL is None and Lazy.CORES > 0:
             Lazy.POOL = Pool(Lazy.CORES)
         self.remote = False
         self.setdepth(0)
@@ -152,7 +155,7 @@ def eval(self):
     def schedule(cls):
         while cls.JOBS:
             next = max(list(cls.JOBS), key=lambda x:x.depth)
-            if next.depth == -1 or next.remote and cls.ACTIVE >= cls.CORES:
+            if next.depth == -1 or next.remote and cls.CORES > 0 and cls.ACTIVE >= cls.CORES:
                 break
             next.startjob()