Add a SimpleBufferPool for uv::Buffer (#1215)

Buffers are reused on a regular basis in many use cases.

wpiutil/src/test/native/cpp/uv/UvBufferTest.cpp

@@ -0,0 +1,50 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2018 FIRST. All Rights Reserved.                             */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include "wpi/uv/Buffer.h"  // NOLINT(build/include_order)
+
+#include "gtest/gtest.h"  // NOLINT(build/include_order)
+
+namespace wpi {
+namespace uv {
+
+TEST(UvSimpleBufferPool, ConstructDefault) {
+  SimpleBufferPool<> pool;
+  auto buf1 = pool.Allocate();
+  ASSERT_EQ(buf1.len, 4096u);
+}
+
+TEST(UvSimpleBufferPool, ConstructSize) {
+  SimpleBufferPool<4> pool{8192};
+  auto buf1 = pool.Allocate();
+  ASSERT_EQ(buf1.len, 8192u);
+}
+
+TEST(UvSimpleBufferPool, ReleaseReuse) {
+  SimpleBufferPool<4> pool;
+  auto buf1 = pool.Allocate();
+  auto buf1copy = buf1;
+  auto origSize = buf1.len;
+  buf1.len = 8;
+  pool.Release(buf1);
+  ASSERT_EQ(buf1.base, nullptr);
+  auto buf2 = pool.Allocate();
+  ASSERT_EQ(buf1copy.base, buf2.base);
+  ASSERT_EQ(buf2.len, origSize);
+}
+
+TEST(UvSimpleBufferPool, ClearRemaining) {
+  SimpleBufferPool<4> pool;
+  auto buf1 = pool.Allocate();
+  pool.Release(buf1);
+  ASSERT_EQ(pool.Remaining(), 1u);
+  pool.Clear();
+  ASSERT_EQ(pool.Remaining(), 0u);
+}
+
+}  // namespace uv
+}  // namespace wpi