From b46835e15ec0441199094e6aa5e583bcaaed8663 Mon Sep 17 00:00:00 2001
From: Max Kellermann <max@musicpd.org>
Date: Thu, 21 Sep 2017 20:31:03 +0200
Subject: [PATCH] util/HugeAllocator: HugeAllocator() returns
 WritableBuffer<void>

---
 src/input/ThreadInputStream.cxx |  9 +++----
 src/util/HugeAllocator.cxx      |  9 +++----
 src/util/HugeAllocator.hxx      | 42 ++++++++++++++++-----------------
 src/util/SliceBuffer.hxx        |  2 +-
 4 files changed, 32 insertions(+), 30 deletions(-)

diff --git a/src/input/ThreadInputStream.cxx b/src/input/ThreadInputStream.cxx
index b9c9587a4..36f77d557 100644
--- a/src/input/ThreadInputStream.cxx
+++ b/src/input/ThreadInputStream.cxx
@@ -50,12 +50,13 @@ ThreadInputStream::Start()
 {
 	assert(buffer == nullptr);
 
-	void *p = HugeAllocate(buffer_size);
-	assert(p != nullptr);
+	auto allocation = HugeAllocate(buffer_size);
+	assert(allocation != nullptr);
 
-	HugeForkCow(p, buffer_size, false);
+	HugeForkCow(allocation.data, allocation.size, false);
 
-	buffer = new CircularBuffer<uint8_t>((uint8_t *)p, buffer_size);
+	buffer = new CircularBuffer<uint8_t>((uint8_t *)allocation.data,
+					     allocation.size);
 	thread.Start();
 }
 
diff --git a/src/util/HugeAllocator.cxx b/src/util/HugeAllocator.cxx
index 6fcdad953..f5d4683be 100644
--- a/src/util/HugeAllocator.cxx
+++ b/src/util/HugeAllocator.cxx
@@ -55,7 +55,7 @@ AlignToPageSize(size_t size) noexcept
 	return (size + ps - 1) / ps * ps;
 }
 
-void *
+WritableBuffer<void>
 HugeAllocate(size_t size)
 {
 	size = AlignToPageSize(size);
@@ -73,7 +73,7 @@ HugeAllocate(size_t size)
 	madvise(p, size, MADV_HUGEPAGE);
 #endif
 
-	return p;
+	return {p, size};
 }
 
 void
@@ -101,7 +101,7 @@ HugeDiscard(void *p, size_t size) noexcept
 
 #elif defined(WIN32)
 
-void *
+WritableBuffer<void>
 HugeAllocate(size_t size)
 {
 	// TODO: use MEM_LARGE_PAGES
@@ -111,7 +111,8 @@ HugeAllocate(size_t size)
 	if (p == nullptr)
 		throw std::bad_alloc();
 
-	return p;
+	// TODO: round size up to the page size
+	return {p, size};
 }
 
 #endif
diff --git a/src/util/HugeAllocator.hxx b/src/util/HugeAllocator.hxx
index 421cf7da4..765b4fc6b 100644
--- a/src/util/HugeAllocator.hxx
+++ b/src/util/HugeAllocator.hxx
@@ -30,6 +30,7 @@
 #ifndef HUGE_ALLOCATOR_HXX
 #define HUGE_ALLOCATOR_HXX
 
+#include "WritableBuffer.hxx"
 #include "Compiler.h"
 
 #include <utility>
@@ -44,9 +45,12 @@
  * need it anymore.  On the downside, this call is expensive.
  *
  * Throws std::bad_alloc on error
+ *
+ * @returns the allocated buffer with a size which may be rounded up
+ * (to the next page size), so callers can take advantage of this
+ * allocation overhead
  */
-gcc_malloc
-void *
+WritableBuffer<void>
 HugeAllocate(size_t size);
 
 /**
@@ -77,8 +81,7 @@ HugeDiscard(void *p, size_t size) noexcept;
 #elif defined(WIN32)
 #include <windows.h>
 
-gcc_malloc
-void *
+WritableBuffer<void>
 HugeAllocate(size_t size);
 
 static inline void
@@ -104,11 +107,10 @@ HugeDiscard(void *p, size_t size) noexcept
 
 #include <stdint.h>
 
-gcc_malloc
-static inline void *
+WritableBuffer<void>
 HugeAllocate(size_t size)
 {
-	return new uint8_t[size];
+	return {new uint8_t[size], size};
 }
 
 static inline void
@@ -134,46 +136,44 @@ HugeDiscard(void *, size_t) noexcept
  * Automatic huge memory allocation management.
  */
 class HugeAllocation {
-	void *data = nullptr;
-	size_t size;
+	WritableBuffer<void> buffer = nullptr;
 
 public:
 	HugeAllocation() = default;
 
 	explicit HugeAllocation(size_t _size)
-		:data(HugeAllocate(_size)), size(_size) {}
+		:buffer(HugeAllocate(_size)) {}
 
 	HugeAllocation(HugeAllocation &&src) noexcept
-		:data(std::exchange(src.data, nullptr)), size(src.size) {}
+		:buffer(std::exchange(src.buffer, nullptr)) {}
 
 	~HugeAllocation() {
-		if (data != nullptr)
-			HugeFree(data, size);
+		if (buffer != nullptr)
+			HugeFree(buffer.data, buffer.size);
 	}
 
 	HugeAllocation &operator=(HugeAllocation &&src) noexcept {
-		std::swap(data, src.data);
-		std::swap(size, src.size);
+		std::swap(buffer, src.buffer);
 		return *this;
 	}
 
 	void ForkCow(bool enable) noexcept {
-		HugeForkCow(data, size, enable);
+		HugeForkCow(buffer.data, buffer.size, enable);
 	}
 
 	void Discard() noexcept {
-		HugeDiscard(data, size);
+		HugeDiscard(buffer.data, buffer.size);
 	}
 
 	void reset() noexcept {
-		if (data != nullptr) {
-			HugeFree(data, size);
-			data = nullptr;
+		if (buffer != nullptr) {
+			HugeFree(buffer.data, buffer.size);
+			buffer = nullptr;
 		}
 	}
 
 	void *get() noexcept {
-		return data;
+		return buffer.data;
 	}
 };
 
diff --git a/src/util/SliceBuffer.hxx b/src/util/SliceBuffer.hxx
index de553fcb4..76e5d3b83 100644
--- a/src/util/SliceBuffer.hxx
+++ b/src/util/SliceBuffer.hxx
@@ -72,7 +72,7 @@ class SliceBuffer {
 public:
 	SliceBuffer(unsigned _count)
 		:n_max(_count),
-		 data((Slice *)HugeAllocate(CalcAllocationSize())) {
+		 data((Slice *)HugeAllocate(CalcAllocationSize()).data) {
 		assert(n_max > 0);
 
 		HugeForkCow(data, CalcAllocationSize(), false);