Properly create zero-initialized local memory.

base/metrics/persistent_memory_allocator.cc

Index: base/metrics/persistent_memory_allocator.cc
diff --git a/base/metrics/persistent_memory_allocator.cc b/base/metrics/persistent_memory_allocator.cc
index bc873fefa0aeebc1b631861d594e55bf4919cc69..39bdb40a6ced245069d479ddb78aacff23e603f7 100644
--- a/base/metrics/persistent_memory_allocator.cc
+++ b/base/metrics/persistent_memory_allocator.cc
@@ -7,6 +7,12 @@
 #include <assert.h>
 #include <algorithm>
 
+#if defined(OS_WIN)
+#include "winbase.h"
+#elif defined(OS_POSIX)
+#include <sys/mman.h>
+#endif
+
 #include "base/files/memory_mapped_file.h"
 #include "base/logging.h"
 #include "base/memory/shared_memory.h"
@@ -716,11 +722,44 @@ LocalPersistentMemoryAllocator::LocalPersistentMemoryAllocator(
     size_t size,
     uint64_t id,
     base::StringPiece name)
-    : PersistentMemoryAllocator(memset(new char[size], 0, size),
+    : PersistentMemoryAllocator(AllocateLocalMemory(size),
                                 size, 0, id, name, false) {}
 
 LocalPersistentMemoryAllocator::~LocalPersistentMemoryAllocator() {
-  delete [] mem_base_;
+  DeallocateLocalMemory(const_cast<char*>(mem_base_), mem_size_);
+}
+
+// static
+void* LocalPersistentMemoryAllocator::AllocateLocalMemory(size_t size) {
+#if defined(OS_WIN)
+  void* address =
+      ::VirtualAlloc(nullptr, size, MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE);
+  DCHECK(address) << ::GetLastError();

[Ilya Sherman, 2016/06/01 23:34:58]

nit: Mebbe use PCHECK, here and elsewhere where you print GetLastError/errno?

[bcwhite, 2016/06/02 13:47:05]

Done.

+  return address;
+#elif defined(OS_POSIX)
+  // MAP_ANON is deprecated on Linux but MAP_ANONYMOUS is not universal on Mac.
+  // MAP_SHARED is not available on Linux <2.4 but required on Mac.

[Ilya Sherman, 2016/06/01 23:34:58]

Would it make more sense to have separate code paths for Linux and Mac, then?

[bcwhite, 2016/06/02 13:47:05]

I considered that but in the end decided that a combination that worked on both
Mac and Linux was most likely to work on any configuration marked "posix"
without having to individually try every specific OS definition.

+  void* address = ::mmap(nullptr, size, PROT_READ | PROT_WRITE,
+                         MAP_ANON | MAP_SHARED, -1, 0);
+  DCHECK_NE(MAP_FAILED, address) << errno;
+  return address;
+#else
+#error This architecture is not (yet) supported.
+#endif
+}
+
+// static
+void LocalPersistentMemoryAllocator::DeallocateLocalMemory(void* memory,
+                                                           size_t size) {
+#if defined(OS_WIN)
+  BOOL success = ::VirtualFree(memory, 0, MEM_DECOMMIT);
+  DCHECK(success) << ::GetLastError();
+#elif defined(OS_POSIX)
+  int result = ::munmap(memory, size);
+  DCHECK_EQ(0, result) << errno;
+#else
+#error This architecture is not (yet) supported.
+#endif
 }