base: Introduce SharedMemoryTracker for POSIX (but not macOS)

base/memory/shared_memory_handle.h

Index: base/memory/shared_memory_handle.h
diff --git a/base/memory/shared_memory_handle.h b/base/memory/shared_memory_handle.h
index dc33eeafa11faef22f73be0d44dd30447e43118b..f5f1f4d358c1b9c065b046dad43a0e2150aa76e7 100644
--- a/base/memory/shared_memory_handle.h
+++ b/base/memory/shared_memory_handle.h
@@ -186,6 +186,34 @@ class BASE_EXPORT SharedMemoryHandle {
 };
 #endif
 
+#if defined(OS_POSIX) && !(defined(OS_MACOSX) && !defined(OS_IOS))

[danakj, 2017/01/25 16:58:13]

can you write this without double negatives? are you meaning to enable this on
IOS?

This should all go into a new file it seems like, this is a separate type with
helper methods for it.

[hajimehoshi, 2017/01/26 10:56:00]

Yeah, as far as I understand correctly, SharedMemory implementation is same in
POSIX except for macOS (not iOS).
Done.

+
+struct SharedMemoryHandleID {

[danakj, 2017/01/25 16:58:12]

Id instead of ID

[hajimehoshi, 2017/01/26 10:56:00]

Done.

+  dev_t device_id;
+  ino_t file_id;
+};
+
+bool GetIDFromSharedMemoryHandle(const SharedMemoryHandle& handle,

[danakj, 2017/01/25 16:58:13]

How about a Populate method on SharedMemoryHandleId?

[hajimehoshi, 2017/01/26 10:56:00]

SharedMemoryHandle is FileDescriptor on POSIX. Adding methods to FileDescriptor
seems controversial. Do you think it is OK?

+                                 SharedMemoryHandleID* id);
+
+std::string GetSharedMemoryHandleIDString(const SharedMemoryHandleID& id);

[danakj, 2017/01/25 16:58:13]

How about a ToString() method?

[hajimehoshi, 2017/01/26 10:56:00]

Done.

+
+struct SharedMemoryHandleIDHash {
+  std::size_t operator()(const SharedMemoryHandleID& id) const {
+    return std::hash<int64_t>()(static_cast<int64_t>(id.device_id)) ^

[danakj, 2017/01/25 16:58:13]

Use HashInts, not xor.
https://cs.chromium.org/chromium/src/base/hash.h?rcl=1485346575&l=96

[hajimehoshi, 2017/01/26 10:56:00]

Done.

+           std::hash<int64_t>()(static_cast<int64_t>(id.file_id));
+  }
+};
+
+struct SharedMemoryHandleIDEqual {

[danakj, 2017/01/25 16:58:13]

why not operator==?

[hajimehoshi, 2017/01/26 10:56:00]

Done.

+  bool operator()(const SharedMemoryHandleID& lhs,
+                  const SharedMemoryHandleID& rhs) const {
+    return lhs.device_id == rhs.device_id && lhs.file_id == rhs.file_id;
+  }
+};
+
+#endif
+
 }  // namespace base
 
 #endif  // BASE_MEMORY_SHARED_MEMORY_HANDLE_H_