Add a templated priority queue class.

Review URL: https://codereview.chromium.org/914003004

4 files changed, 349 insertions, 0 deletions

diff --git a/gyp/core.gypi b/gyp/core.gypi
index 0e2f24f398..608014828e 100644
--- a/gyp/core.gypi
+++ b/gyp/core.gypi
@@ -203,6 +203,7 @@
         '<(skia_src_path)/core/SkTextBlob.cpp',
         '<(skia_src_path)/core/SkTextFormatParams.h',
         '<(skia_src_path)/core/SkTextMapStateProc.h',
+        '<(skia_src_path)/core/SkTDPQueue.h',
         '<(skia_src_path)/core/SkTHashCache.h',
         '<(skia_src_path)/core/SkTLList.h',
         '<(skia_src_path)/core/SkTLS.cpp',
diff --git a/gyp/tests.gypi b/gyp/tests.gypi
index 25e1b7ae8c..625fa866f0 100644
--- a/gyp/tests.gypi
+++ b/gyp/tests.gypi
@@ -202,6 +202,7 @@
     '../tests/StrokerTest.cpp',
     '../tests/SurfaceTest.cpp',
     '../tests/TArrayTest.cpp',
+    '../tests/TDPQueueTest.cpp',
     '../tests/THashCache.cpp',
     '../tests/Time.cpp',
     '../tests/TLSTest.cpp',
diff --git a/src/core/SkTDPQueue.h b/src/core/SkTDPQueue.h
new file mode 100644
index 0000000000..9efde01b66
--- /dev/null
+++ b/src/core/SkTDPQueue.h
@@ -0,0 +1,191 @@
+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkTDPQueue_DEFINED
+#define SkTDPQueue_DEFINED
+
+#include "SkTDArray.h"
+
+/**
+ * This class implements a priority queue. T is the type of the elements in the queue. LESS is a
+ * function that compares two Ts and returns true if the first is higher priority than the second.
+ *
+ * Optionally objects may know their index into the priority queue. The queue will update the index
+ * as the objects move through the queue. This is enabled by using a non-NULL function for INDEX.
+ * When an INDEX function is provided random deletes from the queue are allowed using remove().
+ * Additionally, the * priority is allowed to change as long as priorityDidChange() is called
+ * afterwards. In debug builds the index will be set to -1 before an element is removed from the
+ * queue.
+ */
+template <typename T,
+          bool (*LESS)(const T&, const T&),
+          int* (*INDEX)(const T&) = (int* (*)(const T&))NULL>
+class SkTDPQueue : public SkNoncopyable {
+public:
+    SkTDPQueue() {}
+
+    /** Number of items in the queue. */
+    int count() const { return fArray.count(); }
+
+    /** Gets the next item in the queue without popping it. */
+    const T& peek() const { return fArray[0]; }
+    T& peek() { return fArray[0]; }
+    
+    /** Removes the next item. */
+    void pop() {
+        this->validate();
+        SkDEBUGCODE(if (SkToBool(INDEX)) { *INDEX(fArray[0]) = -1; })
+        if (1 == fArray.count()) {
+            fArray.pop();
+            return;
+        }
+
+        fArray[0] = fArray[fArray.count() - 1];
+        this->setIndex(0);
+        fArray.pop();
+        this->percolateDownIfNecessary(0);
+
+        this->validate();
+    }
+
+    /** Inserts a new item in the queue based on its priority. */
+    void insert(T entry) {
+        this->validate();
+        int index = fArray.count();
+        *fArray.append() = entry;
+        this->setIndex(fArray.count() - 1);
+        this->percolateUpIfNecessary(index);
+        this->validate();
+    }
+
+    /** Random access removal. This requires that the INDEX function is non-NULL. */
+    void remove(T entry) {
+        SkASSERT(NULL != INDEX);
+        int index = *INDEX(entry);
+        SkASSERT(index >= 0 && index < fArray.count());
+        this->validate();
+        SkDEBUGCODE(*INDEX(fArray[index]) = -1;)
+        if (index == fArray.count() - 1) {
+            fArray.pop();
+            return;
+        }
+        fArray[index] = fArray[fArray.count() - 1];
+        fArray.pop();
+        this->setIndex(index);
+        this->percolateUpOrDown(index);
+        this->validate();
+    }
+
+    /** Notification that the priority of an entry has changed. This must be called after an
+        item's priority is changed to maintain correct ordering. Changing the priority is only
+        allowed if an INDEX function is provided. */
+    void priorityDidChange(T entry) {
+        SkASSERT(NULL != INDEX);
+        int index = *INDEX(entry);
+        SkASSERT(index >= 0 && index < fArray.count());
+        this->validate(index);
+        this->percolateUpOrDown(index);
+        this->validate();
+    }
+
+private:
+    static int LeftOf(int x) { SkASSERT(x >= 0); return 2 * x + 1; }
+    static int ParentOf(int x) { SkASSERT(x > 0); return (x - 1) >> 1; }
+
+    void percolateUpOrDown(int index) {
+        SkASSERT(index >= 0);
+        if (!percolateUpIfNecessary(index)) {
+            this->validate(index);
+            this->percolateDownIfNecessary(index);
+        }
+    }
+
+    bool percolateUpIfNecessary(int index) {
+        SkASSERT(index >= 0);
+        bool percolated = false;
+        do {
+            if (0 == index) {
+                this->setIndex(index);
+                return percolated;
+            }
+            int p = ParentOf(index);
+            if (LESS(fArray[index], fArray[p])) {
+                SkTSwap(fArray[index], fArray[p]);
+                this->setIndex(index);
+                index = p;
+                percolated = true;
+            } else {
+                this->setIndex(index);
+                return percolated;
+            }
+            this->validate(index);
+        } while (true);
+    }
+
+    void percolateDownIfNecessary(int index) {
+        SkASSERT(index >= 0);
+        do {
+            int child = LeftOf(index);
+            
+            if (child >= fArray.count()) {
+                // We're a leaf.
+                this->setIndex(index);
+                return;
+            }
+
+            if (child + 1 >= fArray.count()) {
+                // We only have a left child.
+                if (LESS(fArray[child], fArray[index])) {
+                    SkTSwap(fArray[child], fArray[index]);
+                    this->setIndex(child);
+                    this->setIndex(index);
+                    return;
+                }
+            } else if (LESS(fArray[child + 1], fArray[child])) {
+                // The right child is the one we should swap with, if we swap.
+                child++;
+            }
+
+            // Check if we need to swap.
+            if (LESS(fArray[child], fArray[index])) {
+                SkTSwap(fArray[child], fArray[index]);
+                this->setIndex(index);
+                index = child;
+            } else {
+                // We're less than both our children.
+                this->setIndex(index);
+                return;
+            }
+            this->validate(index);
+        } while (true);
+    }
+
+    void setIndex(int index) {
+        SkASSERT(index < fArray.count());
+        if (SkToBool(INDEX)) {
+            *INDEX(fArray[index]) = index;
+        }
+    }
+
+    void validate(int excludedIndex = -1) const {
+#ifdef SK_DEBUG
+        for (int i = 1; i < fArray.count(); ++i) {
+            int p = ParentOf(i);
+            if (excludedIndex != p && excludedIndex != i) {
+                SkASSERT(!(LESS(fArray[i], fArray[p])));
+                SkASSERT(!SkToBool(INDEX) || *INDEX(fArray[i]) == i);
+            }
+        }
+#endif
+    }
+
+    SkTDArray<T> fArray;
+    
+    typedef SkNoncopyable INHERITED;
+};
+
+#endif
diff --git a/tests/TDPQueueTest.cpp b/tests/TDPQueueTest.cpp
new file mode 100644
index 0000000000..70367a7b82
--- /dev/null
+++ b/tests/TDPQueueTest.cpp
@@ -0,0 +1,156 @@
+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkTDPQueue.h"
+#include "SkRandom.h"
+#include "Test.h"
+
+namespace { bool intless(const int& a, const int& b) { return a < b; } }
+
+static void simple_test(skiatest::Reporter* reporter) {
+    SkTDPQueue<int, intless> heap;
+    REPORTER_ASSERT(reporter, 0 == heap.count());
+
+    heap.insert(0);
+    REPORTER_ASSERT(reporter, 1 == heap.count());
+    REPORTER_ASSERT(reporter, 0 == heap.peek());
+    heap.pop();
+    REPORTER_ASSERT(reporter, 0 == heap.count());
+
+    heap.insert(0);
+    heap.insert(1);
+    REPORTER_ASSERT(reporter, 2 == heap.count());
+    REPORTER_ASSERT(reporter, 0 == heap.peek());
+    heap.pop();
+    REPORTER_ASSERT(reporter, 1 == heap.count());
+    REPORTER_ASSERT(reporter, 1 == heap.peek());
+    heap.pop();
+    REPORTER_ASSERT(reporter, 0 == heap.count());
+
+    heap.insert(2);
+    heap.insert(1);
+    heap.insert(0);
+    REPORTER_ASSERT(reporter, 3 == heap.count());
+    REPORTER_ASSERT(reporter, 0 == heap.peek());
+    heap.pop();
+    REPORTER_ASSERT(reporter, 2 == heap.count());
+    REPORTER_ASSERT(reporter, 1 == heap.peek());
+    heap.pop();
+    REPORTER_ASSERT(reporter, 1 == heap.count());
+    REPORTER_ASSERT(reporter, 2 == heap.peek());
+    heap.pop();
+    REPORTER_ASSERT(reporter, 0 == heap.count());
+
+    heap.insert(2);
+    heap.insert(3);
+    heap.insert(0);
+    heap.insert(1);
+    REPORTER_ASSERT(reporter, 4 == heap.count());
+    REPORTER_ASSERT(reporter, 0 == heap.peek());
+    heap.pop();
+    REPORTER_ASSERT(reporter, 3 == heap.count());
+    REPORTER_ASSERT(reporter, 1 == heap.peek());
+    heap.pop();
+    REPORTER_ASSERT(reporter, 2 == heap.count());
+    REPORTER_ASSERT(reporter, 2 == heap.peek());
+    heap.pop();
+    REPORTER_ASSERT(reporter, 1 == heap.count());
+    REPORTER_ASSERT(reporter, 3 == heap.peek());
+    heap.pop();
+    REPORTER_ASSERT(reporter, 0 == heap.count());
+}
+
+struct Dummy {
+    int fValue;
+    int fPriority;
+    mutable int fIndex;
+
+    static bool LessP(Dummy* const& a, Dummy* const& b) { return a->fPriority < b->fPriority; }
+    static int* PQIndex(Dummy* const& dummy) { return &dummy->fIndex; }
+
+    bool operator== (const Dummy& that) const {
+        return fValue == that.fValue && fPriority == that.fPriority;
+    }
+    bool operator!= (const Dummy& that) const { return !(*this == that); }
+};
+
+void random_test(skiatest::Reporter* reporter) {
+    SkRandom random;
+    static const Dummy kSentinel = {-1, -1, -1};
+
+    for (int i = 0; i < 100; ++i) {
+        // Create a random set of Dummy objects.
+        int count = random.nextULessThan(100);
+        SkTDArray<Dummy> array;
+        array.setReserve(count);
+        for (int j = 0; j < count; ++j) {
+            Dummy* dummy = array.append();
+            dummy->fPriority = random.nextS();
+            dummy->fValue = random.nextS();
+            dummy->fIndex = -1;
+            if (*dummy == kSentinel) {
+                array.pop();
+                --j;
+            }
+        }
+
+        // Stick the dummy objects in the pqueue.
+        SkTDPQueue<Dummy*, Dummy::LessP, Dummy::PQIndex> pq;
+        for (int j = 0; j < count; ++j) {
+            pq.insert(&array[j]);
+        }
+        REPORTER_ASSERT(reporter, pq.count() == array.count());
+        for (int j = 0; j < count; ++j) {
+            // every item should have an entry in the queue.
+            REPORTER_ASSERT(reporter, -1 != array[j].fIndex);
+        }
+
+        // Begin the test.
+        while (pq.count()) {
+            // Make sure the top of the queue is really the highest priority.
+            Dummy* top = pq.peek();
+            for (int k = 0; k < count; ++k) {
+                REPORTER_ASSERT(reporter, kSentinel == array[k] ||
+                                            array[k].fPriority >= top->fPriority);
+            }
+            // Do one of three random actions:
+            unsigned action = random.nextULessThan(3);
+            switch (action) {
+                case 0: { // pop the top,
+                    Dummy* top = pq.peek();
+                    REPORTER_ASSERT(reporter, array.begin() <= top && top < array.end());
+                    pq.pop();
+                    *top = kSentinel;
+                    break;
+                }
+                case 1: { // remove a random element,
+                    int item;
+                    do {
+                        item = random.nextULessThan(count);
+                    } while (array[item] == kSentinel);
+                    pq.remove(&array[item]);
+                    array[item] = kSentinel;
+                    break;
+                }
+                case 2: { // or change an element's priority.
+                    int item;
+                    do {
+                        item = random.nextULessThan(count);
+                    } while (array[item] == kSentinel);
+                    array[item].fPriority = random.nextS();
+                    pq.priorityDidChange(&array[item]);
+                    break;
+                }
+            }
+        }
+   }
+}
+
+DEF_TEST(TDPQueueTest, reporter) {
+    simple_test(reporter);
+    random_test(reporter);
+}