[tracing] Add method to create "weak" global dumps

base/trace_event/memory_allocator_dump.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_TRACE_EVENT_MEMORY_ALLOCATOR_DUMP_H_
 #define BASE_TRACE_EVENT_MEMORY_ALLOCATOR_DUMP_H_
 
 #include <stdint.h>
 
 #include <string>
 
 #include "base/base_export.h"
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/trace_event/memory_allocator_dump_guid.h"
 #include "base/values.h"
 
 namespace base {
 namespace trace_event {
 
 class MemoryDumpManager;
 class ProcessMemoryDump;
 class TracedValue;
 
 // Data model for user-land memory allocator dumps.
 class BASE_EXPORT MemoryAllocatorDump {
  public:
+  enum Flag {
+    // A dump marked weak will be removed from tracing. It is used when dump

[petrcermak, 2016/01/18 11:23:46]

nit: "... removed from tracing, unless it was/will be dumped by the same or a
different process without the weak flag."

[ssid, 2016/01/18 16:28:35]

Hm, I think as far as mad is concerned, it means that a dump marked weak is
removed. It can be marked strong later so that it is not removed. These cases
are handled by pmd.
Also "will be dumped without weak" would mean same dump can be dumped twice and
is confusing to the user. The existing comment would prevent the user from using
this flag directly from here instead of usign pmd to modify.

[petrcermak, 2016/01/18 17:18:12]

Good point. My concern is that this suggests that the trace will NOT contain
weak memory allocator dumps, which it WILL (they will be removed in Trace
Viewer).

What about "A dump marked as weak will be removed together with its transitive
owners and descendants in trace post-processing"?

+    // provider is unsure of the existance of memory.

[petrcermak, 2016/01/18 11:23:46]

s/existance/existence/

[petrcermak, 2016/01/18 11:23:46]

nit: s/memory/a block of memory/ (memory always exists)

[ssid, 2016/01/18 16:28:35]

Done.

[ssid, 2016/01/18 16:28:35]

Done.

+    WEAK = 1 << 0,
+  };
+
   // MemoryAllocatorDump is owned by ProcessMemoryDump.
   MemoryAllocatorDump(const std::string& absolute_name,
                       ProcessMemoryDump* process_memory_dump,
+                      const MemoryAllocatorDumpGuid& guid,
+                      uint8_t flags);

[petrcermak, 2016/01/18 11:23:46]

As explained in my comment in ProcessMemoryDump, adding this constructor might
not be necessary.

[ssid, 2016/01/18 16:28:35]

true.

+  MemoryAllocatorDump(const std::string& absolute_name,
+                      ProcessMemoryDump* process_memory_dump,
                       const MemoryAllocatorDumpGuid& guid);
   MemoryAllocatorDump(const std::string& absolute_name,
                       ProcessMemoryDump* process_memory_dump);
   ~MemoryAllocatorDump();
 
   // Standard attribute |name|s for the AddScalar and AddString() methods.
   static const char kNameSize[];          // To represent allocated space.
   static const char kNameObjectCount[];   // To represent number of objects.
 
   // Standard attribute |unit|s for the AddScalar and AddString() methods.
@@ skipping 19 matching lines @@
   const std::string& absolute_name() const { return absolute_name_; }
 
   // Called at trace generation time to populate the TracedValue.
   void AsValueInto(TracedValue* value) const;
 
   // Get the ProcessMemoryDump instance that owns this.
   ProcessMemoryDump* process_memory_dump() const {
     return process_memory_dump_;
   }
 
+  // Use enum Flag to set values.
+  void set_flags(uint8_t flags) { flags_ |= flags; }
+  void unset_flags(uint8_t flags) { flags_ &= ~flags; }
+  uint8_t flags() { return flags_; }
+
   // |guid| is an optional global dump identifier, unique across all processes
   // within the scope of a global dump. It is only required when using the
   // graph APIs (see TODO_method_name) to express retention / suballocation or
   // cross process sharing. See crbug.com/492102 for design docs.
   // Subsequent MemoryAllocatorDump(s) with the same |absolute_name| are
   // expected to have the same guid.
   const MemoryAllocatorDumpGuid& guid() const { return guid_; }
 
   TracedValue* attributes_for_testing() const { return attributes_.get(); }
 
  private:
   const std::string absolute_name_;
   ProcessMemoryDump* const process_memory_dump_;  // Not owned (PMD owns this).
   scoped_refptr<TracedValue> attributes_;
   MemoryAllocatorDumpGuid guid_;
+  uint8_t flags_;  // See enum Flag.
 
   // A local buffer for Sprintf conversion on fastpath. Avoids allocating
   // temporary strings on each AddScalar() call.
   std::string string_conversion_buffer_;
 
   DISALLOW_COPY_AND_ASSIGN(MemoryAllocatorDump);
 };
 
 }  // namespace trace_event
 }  // namespace base
 
 #endif  // BASE_TRACE_EVENT_MEMORY_ALLOCATOR_DUMP_H_