Add pop_back() to GrAllocator and add unit test.

BUG=skia:2889
R=robertphillips@google.com

Author: bsalomon@google.com

Review URL: https://codereview.chromium.org/538183002

gyp/tests.gypi

@@ -108,6 +108,7 @@
     '../tests/GrBinHashKeyTest.cpp',
     '../tests/GrContextFactoryTest.cpp',
     '../tests/GrDrawTargetTest.cpp',
+    '../tests/GrAllocatorTest.cpp',
     '../tests/GrMemoryPoolTest.cpp',
     '../tests/GrOrderedSetTest.cpp',
     '../tests/GrGLSLPrettyPrintTest.cpp',

src/gpu/GrAllocator.h

@@ -60,6 +60,24 @@ public:
         return ret;
     }
 
+    /**
+     * Remove the last item, only call if count() != 0
+     */
+    void pop_back() {
+        SkASSERT(fCount);
+        SkASSERT(fInsertionIndexInBlock > 0);
+        --fInsertionIndexInBlock;
+        --fCount;
+        if (0 == fInsertionIndexInBlock) {
+            // Never delete the first block
+            if (fBlocks.count() > 1) {
+                sk_free(fBlocks.back());
+                fBlocks.pop_back();
+                fInsertionIndexInBlock = fItemsPerBlock;
+            }
+        }
+    }
+
     /**
      * Removes all added items.
      */
@@ -109,7 +127,6 @@ public:
         return (const char*)(fBlocks.back()) + (fInsertionIndexInBlock - 1) * fItemSize;
     }
 
-
     /**
      * Iterates through the allocator. This is faster than using operator[] when walking linearly
      * through the allocator.
@@ -239,6 +256,14 @@ public:
         return *(T*)item;
     }
 
+    /**
+     * Remove the last item, only call if count() != 0
+     */
+    void pop_back() {
+        this->back().~T();
+        fAllocator.pop_back();
+    }
+
     /**
      * Removes all added items.
      */

tests/GrAllocatorTest.cpp

@@ -0,0 +1,103 @@
+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "Test.h"
+// This is a GPU-backend specific test
+#if SK_SUPPORT_GPU
+#include "GrAllocator.h"
+
+namespace {
+struct C {
+    C() : fID(-1) { ++gInstCnt; }
+    C(int id) : fID(id) { ++gInstCnt; }
+    ~C() { --gInstCnt; }
+    int fID;
+
+    static int gInstCnt;
+};
+
+int C::gInstCnt = 0;
+}
+
+static void check_allocator_helper(GrTAllocator<C>* allocator, int cnt, int popCnt,
+                                   skiatest::Reporter* reporter);
+
+// Adds cnt items to the allocator, tests the cnts and iterators, pops popCnt items and checks
+// again. Finally it resets the allocator and checks again.
+static void check_allocator(GrTAllocator<C>* allocator, int cnt, int popCnt,
+                            skiatest::Reporter* reporter) {
+    SkASSERT(NULL != allocator);
+    SkASSERT(allocator->empty());
+    for (int i = 0; i < cnt; ++i) {
+        // Try both variations of push_back().
+        if (i % 1) {
+            allocator->push_back(C(i));
+        } else {
+            allocator->push_back() = C(i);
+        }
+    }
+    check_allocator_helper(allocator, cnt, popCnt, reporter);
+    allocator->reset();
+    check_allocator_helper(allocator, 0, 0, reporter);
+}
+
+// Checks that the allocator has the correct count, etc and that the element IDs are correct.
+// Then pops popCnt items and checks again.
+static void check_allocator_helper(GrTAllocator<C>* allocator, int cnt, int popCnt,
+                                   skiatest::Reporter* reporter) {
+    REPORTER_ASSERT(reporter, (0 == cnt) == allocator->empty());
+    REPORTER_ASSERT(reporter, cnt == allocator->count());
+    REPORTER_ASSERT(reporter, cnt == C::gInstCnt);
+
+    GrTAllocator<C>::Iter iter(allocator);
+    for (int i = 0; i < cnt; ++i) {
+        REPORTER_ASSERT(reporter, iter.next() && i == iter.get()->fID);
+    }
+    REPORTER_ASSERT(reporter, !iter.next());
+    if (cnt > 0) {
+        REPORTER_ASSERT(reporter, cnt-1 == allocator->back().fID);
+    }
+
+    if (popCnt > 0) {
+        for (int i = 0; i < popCnt; ++i) {
+            allocator->pop_back();
+        }
+        check_allocator_helper(allocator, cnt - popCnt, 0, reporter);
+    }
+}
+
+DEF_TEST(GrAllocator, reporter) {
+
+    // Test combinations of allocators with and without stack storage and with different block
+    // sizes.
+    SkTArray<GrTAllocator<C>*> allocators;
+    GrTAllocator<C> a1(1);
+    allocators.push_back(&a1);
+    GrTAllocator<C> a2(2);
+    allocators.push_back(&a2);
+    GrTAllocator<C> a5(5);
+    allocators.push_back(&a5);
+
+    GrSTAllocator<1, C> sa1;
+    allocators.push_back(&a1);
+    GrSTAllocator<3, C> sa3;
+    allocators.push_back(&sa3);
+    GrSTAllocator<4, C> sa4;
+    allocators.push_back(&sa4);
+
+    for (int i = 0; i < allocators.count(); ++i) {
+        check_allocator(allocators[i], 0, 0, reporter);
+        check_allocator(allocators[i], 1, 1, reporter);
+        check_allocator(allocators[i], 2, 2, reporter);
+        check_allocator(allocators[i], 10, 1, reporter);
+        check_allocator(allocators[i], 10, 5, reporter);
+        check_allocator(allocators[i], 10, 10, reporter);
+        check_allocator(allocators[i], 100, 10, reporter);
+    }
+}
+
+#endif