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extern/stdcxx/4.2.1/examples/tutorial/icecream.cpp

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+/**************************************************************************
+ *
+ * icecream.cpp - Priority queue example program.
+ *
+ * $Id: icecream.cpp 595289 2007-11-15 12:34:31Z faridz $
+ *
+ ***************************************************************************
+ *
+ * Licensed to the Apache Software  Foundation (ASF) under one or more
+ * contributor  license agreements.  See  the NOTICE  file distributed
+ * with  this  work  for  additional information  regarding  copyright
+ * ownership.   The ASF  licenses this  file to  you under  the Apache
+ * License, Version  2.0 (the  "License"); you may  not use  this file
+ * except in  compliance with the License.   You may obtain  a copy of
+ * the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the  License is distributed on an  "AS IS" BASIS,
+ * WITHOUT  WARRANTIES OR CONDITIONS  OF ANY  KIND, either  express or
+ * implied.   See  the License  for  the  specific language  governing
+ * permissions and limitations under the License.
+ *
+ * Copyright 1994-2006 Rogue Wave Software.
+ * 
+ **************************************************************************/
+
+#include <algorithm>   // for random_shuffle()
+#include <iostream>    // for cout
+#include <queue>       // for queue
+#include <vector>      // for vector
+
+#include <examples.h>
+
+
+// Execution event in a descrete event driven simulation.
+class event {
+public:
+    // Construct sets time of event.
+    event (unsigned int t) : time (t)
+        { }
+
+    // Execute event by invoking this method.
+    virtual void processEvent () = 0;
+
+    const unsigned int time;
+};
+
+struct eventComparator {
+    bool operator() (const event * left, const event * right) const {
+        return left->time > right->time;
+    }
+};
+
+
+// Framework for discrete event-driven simulations.
+class simulation {
+public:
+    simulation () : time (0), eventQueue () 
+        {}
+    void run ();
+    void  scheduleEvent (event * newEvent) {
+        eventQueue.push (newEvent);
+    }
+    unsigned int time;
+protected:
+    std::priority_queue<event*,
+                        std::vector<event *, std::allocator<event*> >,
+                        eventComparator> eventQueue;
+};
+
+
+void simulation::run () {
+
+    while (! eventQueue.empty ()) {
+
+        event * nextEvent = eventQueue.top ();
+        eventQueue.pop ();
+        time = nextEvent->time;
+        nextEvent->processEvent ();
+        delete nextEvent;
+    }
+}
+
+
+//  Ice cream store simulation.
+class storeSimulation : public simulation {
+public:
+    storeSimulation () : simulation (), freeChairs (35), profit (0.0)
+        { }
+    bool canSeat (unsigned int numberOfPeople);
+    void order   (unsigned int numberOfScoops);
+    void leave   (unsigned int numberOfPeople);
+    // Data fields.
+    unsigned int freeChairs;
+    double       profit;  
+} theSimulation;
+
+
+class arriveEvent : public event {
+public:
+    arriveEvent (unsigned int t, unsigned int groupSize)
+        : event (t), size (groupSize)
+        { }
+    virtual void processEvent ();
+private:
+    unsigned int size;
+};
+
+
+class orderEvent : public event {
+public:
+    orderEvent (unsigned int t, unsigned int groupSize)
+        : event (t), size (groupSize)
+        { }
+    virtual void processEvent ();
+private:
+    unsigned int size;
+};
+
+
+class leaveEvent : public event
+{
+public:
+    leaveEvent (unsigned int t, unsigned int groupSize)
+        : event (t), size (groupSize)
+        { }
+    virtual void processEvent ();
+private:
+    unsigned int size;
+};
+
+
+// returns a random integer between 0 and n with n <= 32767 <= INT_MAX
+int irand (int n)
+{
+    static int seq[] = {
+        0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0xa, 0xb, 0xc, 0xd, 0xe, 0xf
+    };
+
+    std::random_shuffle (seq, seq + sizeof seq / sizeof *seq);
+
+    const int rnd = (seq [0] << 11) | (seq [1] << 8) | (seq [2] << 4) + seq [3];
+
+    return rnd % n;
+}
+
+
+void arriveEvent::processEvent () {
+
+    if (theSimulation.canSeat (size))
+        theSimulation.scheduleEvent
+            (new orderEvent (time + 1 + irand (4), size));
+}
+
+
+void orderEvent::processEvent () {
+
+    // Each person orders some number of scoops.
+    for (unsigned int i = 0; i < size; i++)
+        theSimulation.order (1 + irand (4));
+
+    // Then we schedule the leave event.
+    theSimulation.scheduleEvent
+        (new leaveEvent (time + 1 + irand (10), size));
+}
+
+
+void leaveEvent::processEvent () {
+
+    theSimulation.leave (size);
+}
+
+
+// If sufficient room then seat customers.
+bool storeSimulation::canSeat (unsigned int numberOfPeople) {
+
+    std::cout << "Time: " << time;
+    std::cout << " group of " << numberOfPeople << " customers arrives";
+
+    if (numberOfPeople < freeChairs) {
+        std::cout << " is seated\n";
+        freeChairs -= numberOfPeople;
+        return true;
+    }
+    else {
+        std::cout << " no room, they leave\n";
+        return false;
+    }
+}
+
+
+// Service icecream, compute profits.
+void storeSimulation::order (unsigned int numberOfScoops) {
+
+    std::cout << "Time: " << time << " serviced order for "
+              << numberOfScoops << '\n';
+    profit += 0.35 * numberOfScoops;
+}
+
+
+// People leave, free up chairs.
+void storeSimulation::leave (unsigned int numberOfPeople) {
+
+    std::cout << "Time: " << time << " group of size "
+              << numberOfPeople << " leaves\n";
+    freeChairs += numberOfPeople;
+}
+
+
+int main () {
+
+    std::cout << "Ice Cream Store simulation from Chapter 9\n";
+
+    // Load queue with some number of initial events.
+    for (unsigned t = 0; t < 20; t += irand (6)) {
+
+        std::cout << "pumping queue with event " << t << '\n';
+        theSimulation.scheduleEvent (new arriveEvent (t, 1 + irand (4)));
+    }
+
+    // Run the simulation.
+    theSimulation.run ();
+
+    std::cout << "Total profits " << theSimulation.profit
+              << "\nEnd of ice cream store simulation\n";
+
+    return 0;
+}