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      1 // Copyright 2016 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #ifndef BASE_TRACE_EVENT_CATEGORY_REGISTRY_H_
      6 #define BASE_TRACE_EVENT_CATEGORY_REGISTRY_H_
      7 
      8 #include <stddef.h>
      9 #include <stdint.h>
     10 
     11 #include "base/base_export.h"
     12 #include "base/logging.h"
     13 
     14 namespace base {
     15 namespace trace_event {
     16 
     17 struct TraceCategory;
     18 class TraceCategoryTest;
     19 class TraceLog;
     20 
     21 // Allows fast and thread-safe acces to the state of all tracing categories.
     22 // All the methods in this class can be concurrently called on multiple threads,
     23 // unless otherwise noted (e.g., GetOrCreateCategoryLocked).
     24 // The reason why this is a fully static class with global state is to allow to
     25 // statically define known categories as global linker-initialized structs,
     26 // without requiring static initializers.
     27 class BASE_EXPORT CategoryRegistry {
     28  public:
     29   // Allows for-each iterations over a slice of the categories array.
     30   class Range {
     31    public:
     32     Range(TraceCategory* begin, TraceCategory* end) : begin_(begin), end_(end) {
     33       DCHECK_LE(begin, end);
     34     }
     35     TraceCategory* begin() const { return begin_; }
     36     TraceCategory* end() const { return end_; }
     37 
     38    private:
     39     TraceCategory* const begin_;
     40     TraceCategory* const end_;
     41   };
     42 
     43   // Known categories.
     44   static TraceCategory* const kCategoryExhausted;
     45   static TraceCategory* const kCategoryMetadata;
     46   static TraceCategory* const kCategoryAlreadyShutdown;
     47 
     48   // Returns a category entry from the Category.state_ptr() pointer.
     49   // TODO(primiano): trace macros should just keep a pointer to the entire
     50   // TraceCategory, not just the enabled state pointer. That would remove the
     51   // need for this function and make everything cleaner at no extra cost (as
     52   // long as the |state_| is the first field of the struct, which can be
     53   // guaranteed via static_assert, see TraceCategory ctor).
     54   static const TraceCategory* GetCategoryByStatePtr(
     55       const uint8_t* category_state);
     56 
     57   // Returns a category from its name or nullptr if not found.
     58   // The output |category| argument is an undefinitely lived pointer to the
     59   // TraceCategory owned by the registry. TRACE_EVENTx macros will cache this
     60   // pointer and use it for checks in their fast-paths.
     61   static TraceCategory* GetCategoryByName(const char* category_name);
     62 
     63   static bool IsBuiltinCategory(const TraceCategory*);
     64 
     65  private:
     66   friend class TraceCategoryTest;
     67   friend class TraceLog;
     68   using CategoryInitializerFn = void (*)(TraceCategory*);
     69 
     70   // Only for debugging/testing purposes, is a no-op on release builds.
     71   static void Initialize();
     72 
     73   // Resets the state of all categories, to clear up the state between tests.
     74   static void ResetForTesting();
     75 
     76   // Used to get/create a category in the slow-path. If the category exists
     77   // already, this has the same effect of GetCategoryByName and returns false.
     78   // If not, a new category is created and the CategoryInitializerFn is invoked
     79   // before retuning true. The caller must guarantee serialization: either call
     80   // this method from a single thread or hold a lock when calling this.
     81   static bool GetOrCreateCategoryLocked(const char* category_name,
     82                                         CategoryInitializerFn,
     83                                         TraceCategory**);
     84 
     85   // Allows to iterate over the valid categories in a for-each loop.
     86   // This includes builtin categories such as __metadata.
     87   static Range GetAllCategories();
     88 };
     89 
     90 }  // namespace trace_event
     91 }  // namespace base
     92 
     93 #endif  // BASE_TRACE_EVENT_CATEGORY_REGISTRY_H_
     94