From e9b9584a587af65817fe0d04bedd939ec004a185 Mon Sep 17 00:00:00 2001
From: Tor Egge <Tor.Egge@online.no>
Date: Wed, 9 Feb 2022 16:22:31 +0100
Subject: Add reset and create methods to vespalib::Array.

---
 vespalib/src/tests/array/array_test.cpp    | 48 ++++++++++++++++++++++++++++++
 vespalib/src/vespa/vespalib/util/alloc.h   |  7 +++++
 vespalib/src/vespa/vespalib/util/array.h   |  2 ++
 vespalib/src/vespa/vespalib/util/array.hpp | 15 ++++++++++
 4 files changed, 72 insertions(+)

diff --git a/vespalib/src/tests/array/array_test.cpp b/vespalib/src/tests/array/array_test.cpp
index 719623c9401..5f80ee893da 100644
--- a/vespalib/src/tests/array/array_test.cpp
+++ b/vespalib/src/tests/array/array_test.cpp
@@ -2,6 +2,7 @@
 
 #include <vespa/vespalib/stllike/string.h>
 #include <vespa/vespalib/testkit/testapp.h>
+#include <vespa/vespalib/test/memory_allocator_observer.h>
 #include <vespa/vespalib/util/array.hpp>
 #include <vespa/vespalib/util/size_literals.h>
 #include <deque>
@@ -27,6 +28,11 @@ std::ostream & operator << (std::ostream & os, const Array<T> & a)
 
 }
 
+using alloc::Alloc;
+using alloc::MemoryAllocator;
+using MyMemoryAllocator = vespalib::alloc::test::MemoryAllocatorObserver;
+using AllocStats = MyMemoryAllocator::Stats;
+
 class Clever {
 public:
     Clever() : _counter(&_global) { (*_counter)++; }
@@ -351,4 +357,46 @@ TEST_F("require that try_unreserve() succeedes if mmap can be shrinked", Unreser
     EXPECT_EQUAL(oldPtr, newPtr);
 }
 
+struct Fixture {
+    AllocStats stats;
+    std::unique_ptr<MemoryAllocator> allocator;
+    Alloc initial_alloc;
+    Array<int> arr;
+
+    Fixture();
+    ~Fixture();
+};
+
+Fixture::Fixture()
+    : stats(),
+      allocator(std::make_unique<MyMemoryAllocator>(stats)),
+      initial_alloc(Alloc::alloc_with_allocator(allocator.get())),
+      arr(initial_alloc)
+{
+}
+
+Fixture::~Fixture() = default;
+
+TEST_F("require that memory allocator can be set", Fixture)
+{
+    f.arr.resize(1);
+    EXPECT_EQUAL(AllocStats(1, 0), f.stats);
+}
+
+TEST_F("require that memory allocator is preserved across reset", Fixture)
+{
+    f.arr.resize(1);
+    f.arr.reset();
+    f.arr.resize(1);
+    EXPECT_EQUAL(AllocStats(2, 1), f.stats);
+}
+
+TEST_F("require that created array uses same memory allocator", Fixture)
+{
+    auto arr2 = f.arr.create();
+    EXPECT_EQUAL(AllocStats(0, 0), f.stats);
+    arr2.resize(1);
+    EXPECT_EQUAL(AllocStats(1, 0), f.stats);
+}
+
 TEST_MAIN() { TEST_RUN_ALL(); }
diff --git a/vespalib/src/vespa/vespalib/util/alloc.h b/vespalib/src/vespa/vespalib/util/alloc.h
index d25fb6f6a7c..4066894b4e3 100644
--- a/vespalib/src/vespa/vespalib/util/alloc.h
+++ b/vespalib/src/vespa/vespalib/util/alloc.h
@@ -62,6 +62,13 @@ public:
         std::swap(_alloc, rhs._alloc);
         std::swap(_allocator, rhs._allocator);
     }
+    void reset() {
+        if (_alloc.first != nullptr) {
+            _allocator->free(_alloc);
+            _alloc.first = nullptr;
+            _alloc.second = 0u;
+        }
+    }
     Alloc create(size_t sz) const noexcept {
         return (sz == 0) ? Alloc(_allocator) : Alloc(_allocator, sz);
     }
diff --git a/vespalib/src/vespa/vespalib/util/array.h b/vespalib/src/vespa/vespalib/util/array.h
index 30d87cd98f6..cb5d5c7cc63 100644
--- a/vespalib/src/vespa/vespalib/util/array.h
+++ b/vespalib/src/vespa/vespalib/util/array.h
@@ -135,6 +135,7 @@ public:
         std::destroy(array(0), array(_sz));
         _sz = 0;
     }
+    void reset();
     bool empty() const                      { return _sz == 0; }
     T & operator [] (size_t i)              { return *array(i); }
     const T & operator [] (size_t i) const  { return *array(i); }
@@ -145,6 +146,7 @@ public:
         rhs._sz = 0;
         return std::move(rhs._array);
     }
+    Array<T> create() const;
 private:
     T *       array(size_t i)       { return static_cast<T *>(_array.get()) + i; }
     const T * array(size_t i) const { return static_cast<const T *>(_array.get()) + i; }
diff --git a/vespalib/src/vespa/vespalib/util/array.hpp b/vespalib/src/vespa/vespalib/util/array.hpp
index e9070f5759c..72178f0391b 100644
--- a/vespalib/src/vespa/vespalib/util/array.hpp
+++ b/vespalib/src/vespa/vespalib/util/array.hpp
@@ -205,5 +205,20 @@ void Array<T>::cleanup()
     Alloc().swap(_array);
 }
 
+template <typename T>
+void Array<T>::reset()
+{
+    std::destroy(array(0), array(_sz));
+    _sz = 0;
+    _array.reset();
+}
+
+template <typename T>
+Array<T>
+Array<T>::create() const
+{
+    return Array<T>(_array); // Use same memory allocator
+}
+
 }
 
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