Add methods to base::SharedMemory to replace common SharedMemoryHandle operations.

base/memory/shared_memory_posix.cc

Index: base/memory/shared_memory_posix.cc
diff --git a/base/memory/shared_memory_posix.cc b/base/memory/shared_memory_posix.cc
index 2dc08a14ca24ec2c441173b639dd2b5030264389..33295813ef17dfa14fa139e1ee2fa12cc0c1b10d 100644
--- a/base/memory/shared_memory_posix.cc
+++ b/base/memory/shared_memory_posix.cc
@@ -108,6 +108,26 @@ size_t SharedMemory::GetHandleLimit() {
   return base::GetMaxFds();
 }
 
+#if defined(OS_WIN) || defined(OS_POSIX)

[Nico, 2015/05/29 06:50:23]

this is just "everywhere", right?

[erikchen, 2015/05/29 18:30:24]

I guess so. Removed preprocessor conditionals.

+// static
+SharedMemoryHandle SharedMemory::ShallowCopyOfHandle(
+    const SharedMemoryHandle& handle) {
+  return handle;

[Nico, 2015/05/29 06:50:24]

The CL you link to doesn't modify this function. Is it necessary to wrap this,
or can callers just use " = "? Assignment of handles is fairly well understood,
I feel.

[erikchen, 2015/05/29 18:30:24]

I think it's semantically important to not use assignment of handles, since it
loses information about whether the copy is intended to be shallow or deep. For
example, right now, on POSIX, SharedMemoryHandle is typedefed to FileDescriptor,
and assignment copies the "auto_close" parameter without duping the fd, which
semantically doesn't make any sense. (The existing code happens to work because
locations that make shallow copies of SharedMemoryHandle end up dup()ing the
handle before turning it into a base::SharedMemory.

I updated the definition to fix the "auto_close" bug.

+}
+#endif
+
+#if defined(OS_POSIX)
+// static
+SharedMemoryHandle SharedMemory::DeepCopyOfHandle(

[Nico, 2015/05/29 06:50:24]

CloneHandle() maybe?

[erikchen, 2015/05/29 18:30:24]

If you really want me to change the verb, the canonical verb we use in Chrome is
"Duplicate" when it comes to SharedMemoryHandles. That being said, that verb is
less explicit about shallow/deep copy, which is why I prefer this version.

+    const SharedMemoryHandle& handle,
+    bool clean_up_resources_on_destruction) {
+  int duped_handle = HANDLE_EINTR(dup(handle.fd));
+  if (duped_handle < 0)
+    return base::SharedMemory::NULLHandle();
+  return base::FileDescriptor(duped_handle, clean_up_resources_on_destruction);
+}
+#endif
+
 bool SharedMemory::CreateAndMapAnonymous(size_t size) {
   return CreateAnonymous(size) && Map(size);
 }