Add fibonacci examples that uses futures (#284)

examples/fibonacci/README.rst

@@ -1,5 +1,23 @@
 
 **Recursive Parallel Fibonacci**
 
+These examples calculate the Fibonacci number at a given index provided
+by the user.
+
 This example is meant to illustrate the use of ``charm.pool`` and nested
 parallelism (creating parallel tasks from other parallel tasks).
+
+**Different versions**
+
+There are 3 implementations:
+
+-  fib.py (Uses the charm pool to create tasks recursively and assign them to workers)
+-  fib-numba.py (Uses the Numba JIT compiler for an efficient implementation)
+-  fibonacci_with_futures.py (Uses Charm4Py futures to store the results of intermediate calculations)
+
+**Usage**
+
+$ python3 -m charmrun.start +p<N> <file_name> <index>
+
+where N is the number of PEs and index is the Fibonacci number you want to calculate. For example, index=6
+should return 8.

examples/fibonacci/fibonacci_with_futures.py

@@ -0,0 +1,57 @@
+from charm4py import charm, Chare, Future, coro
+#modeled after the charm with futures example in the charm++ textbook
+
+THRESHOLD = 20
+
+class Fib(Chare):
+
+    @coro
+    def __init__(self, n, future):
+        if n < THRESHOLD:
+            res = self.seqFib(n)
+            future.send(res)
+        else:
+            # Create two futures for the recursive calls
+            f1 = Future()
+            f2 = Future()
+
+            # Create two new chares with parameters n - 1, n - 2, and their corresponding futures
+            childfib1 = Chare(Fib, args=[n - 1, f1])
+            childfib2 = Chare(Fib, args=[n - 2, f2])
+
+            # Wait for the results
+            val1 = f1.get()
+            val2 = f2.get()
+            res = val1 + val2
+
+            # Send result back to the parent chare
+            future.send(res)
+
+    def seqFib(self, n):
+        if n <= 1:
+            return n
+        else:
+            return self.seqFib(n - 1) + self.seqFib(n - 2)
+
+@coro
+def main(args):
+    if len(args) < 2:
+        print("Possible Usage: charmrun ++local +p4 fibonacciWithFutures.py 20 <n>")
+        charm.exit()
+    n = int(args[1])
+    if n < 0:
+        print("n must be a non-negative integer")
+        charm.exit()
+
+    # Create a future
+    f = Future()
+
+    # Create a Fib chare to start the calculations
+    fibChare = Chare(Fib, args=[n, f])
+
+    # Get the value of the future (blocks until received)
+    res = f.get()
+    print("The requested Fibonacci number is:", res)
+    charm.exit()
+
+charm.start(main)