Measure and report time between user-space process crashes.

counter.h

 // Copyright (c) 2010 The Chromium OS 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 METRICS_COUNTER_H_
 #define METRICS_COUNTER_H_
 
 #include <gtest/gtest_prod.h>  // for FRIEND_TEST
 
 namespace chromeos_metrics {
 
 // TaggedCounter maintains a persistent storage (i.e., a file)
 // aggregation counter for a given tag (e.g., day, hour) that survives
 // system shutdowns, reboots and crashes, as well as daemon process
 // restarts. The counter object is initialized by pointing to the
 // persistent storage file and providing a callback used for reporting
 // aggregated data.  The counter can then be updated with additional
 // event counts.  The aggregated count is reported through the
 // callback when the counter is explicitly flushed or when data for a
 // new tag arrives.
 class TaggedCounterInterface {
  public:
   // Callback type used for reporting aggregated or flushed data.
   // Once this callback is invoked by the counter, the reported
-  // aggregated data is discarded. Only aggregated data with positive
-  // counts is reported.
+  // aggregated data is discarded.
   //
   // |handle| is the |reporter_handle| pointer passed through Init.
   // |tag| is the tag associated with the aggregated count.
   // |count| is aggregated count.
   typedef void (*Reporter)(void* handle, int tag, int count);
 
   virtual ~TaggedCounterInterface() {}
 
   // Initializes the counter by providing the persistent storage
   // location |filename| and a |reporter| callback for reporting
@@ skipping 80 matching lines @@
   void ReadRecord(int fd);
 
   // If there's an existing valid record and either |flush| is true,
   // or the new |tag| is different than the old one, reports the
   // aggregated data through the reporter callback and resets the
   // cached record.
   void ReportRecord(int tag, bool flush);
 
   // Updates the cached record given the new |tag| and |count|. This
   // method expects either a null cached record, or a valid cached
-  // record with the same tag as |tag|.
-  void UpdateRecord(int tag, int count);
+  // record with the same tag as |tag|. If |flush| is true, the method
+  // asserts that the cached record is null and returns.
+  void UpdateRecord(int tag, int count, bool flush);
 
   // If the cached record state is dirty, updates the persistent
   // storage specified through file descriptor |fd| and switches the
   // record state to non-dirty.
   void WriteRecord(int fd);
 
   // Persistent storage file path.
   const char* filename_;
 
   // Aggregated data reporter callback and handle to pass-through.
   Reporter reporter_;
   void* reporter_handle_;
 
   // Current cached aggregation record.
   Record record_;
 
   // Current cached aggregation record state.
   RecordState record_state_;
 };
 
 }  // namespace chromeos_metrics
 
 #endif  // METRICS_COUNTER_H_