Update from https://crrev.com/304418

base/metrics/histogram.h

Index: base/metrics/histogram.h
diff --git a/base/metrics/histogram.h b/base/metrics/histogram.h
index 43e7462fe0533b29b6592a0865f765467c02e236..9ee172e6cdadcf8e1493cffb24e3d5f45ca65be3 100644
--- a/base/metrics/histogram.h
+++ b/base/metrics/histogram.h
@@ -50,9 +50,12 @@
 // at the low end of the histogram scale, but allows the histogram to cover a
 // gigantic range with the addition of very few buckets.
 
-// Usually we use macros to define and use a histogram. These macros use a
-// pattern involving a function static variable, that is a pointer to a
-// histogram.  This static is explicitly initialized on any thread
+// Usually we use macros to define and use a histogram, which are defined in
+// base/metrics/histogram_macros.h. Note: Callers should include that header
+// directly if they only access the histogram APIs through macros.
+//
+// Macros use a pattern involving a function static variable, that is a pointer
+// to a histogram.  This static is explicitly initialized on any thread
 // that detects a uninitialized (NULL) pointer.  The potentially racy
 // initialization is not a problem as it is always set to point to the same
 // value (i.e., the FactoryGet always returns the same value).  FactoryGet
@@ -67,7 +70,6 @@
 #include <string>
 #include <vector>
 
-#include "base/atomicops.h"
 #include "base/base_export.h"
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
@@ -76,6 +78,8 @@
 #include "base/memory/scoped_ptr.h"
 #include "base/metrics/bucket_ranges.h"
 #include "base/metrics/histogram_base.h"
+// TODO(asvitkine): Migrate callers to to include this directly and remove this.
+#include "base/metrics/histogram_macros.h"
 #include "base/metrics/histogram_samples.h"
 #include "base/time/time.h"
 
@@ -84,234 +88,11 @@ class PickleIterator;
 
 namespace base {
 
-class Lock;
-//------------------------------------------------------------------------------
-// Histograms are often put in areas where they are called many many times, and
-// performance is critical.  As a result, they are designed to have a very low
-// recurring cost of executing (adding additional samples).  Toward that end,
-// the macros declare a static pointer to the histogram in question, and only
-// take a "slow path" to construct (or find) the histogram on the first run
-// through the macro.  We leak the histograms at shutdown time so that we don't
-// have to validate using the pointers at any time during the running of the
-// process.
-
-// The following code is generally what a thread-safe static pointer
-// initialization looks like for a histogram (after a macro is expanded).  This
-// sample is an expansion (with comments) of the code for
-// LOCAL_HISTOGRAM_CUSTOM_COUNTS().
-
-/*
-  do {
-    // The pointer's presence indicates the initialization is complete.
-    // Initialization is idempotent, so it can safely be atomically repeated.
-    static base::subtle::AtomicWord atomic_histogram_pointer = 0;
-
-    // Acquire_Load() ensures that we acquire visibility to the pointed-to data
-    // in the histogram.
-    base::Histogram* histogram_pointer(reinterpret_cast<base::Histogram*>(
-        base::subtle::Acquire_Load(&atomic_histogram_pointer)));
-
-    if (!histogram_pointer) {
-      // This is the slow path, which will construct OR find the matching
-      // histogram.  FactoryGet includes locks on a global histogram name map
-      // and is completely thread safe.
-      histogram_pointer = base::Histogram::FactoryGet(
-          name, min, max, bucket_count, base::HistogramBase::kNoFlags);
-
-      // Use Release_Store to ensure that the histogram data is made available
-      // globally before we make the pointer visible.
-      // Several threads may perform this store, but the same value will be
-      // stored in all cases (for a given named/spec'ed histogram).
-      // We could do this without any barrier, since FactoryGet entered and
-      // exited a lock after construction, but this barrier makes things clear.
-      base::subtle::Release_Store(&atomic_histogram_pointer,
-          reinterpret_cast<base::subtle::AtomicWord>(histogram_pointer));
-    }
-
-    // Ensure calling contract is upheld, and the name does NOT vary.
-    DCHECK(histogram_pointer->histogram_name() == constant_histogram_name);
-
-    histogram_pointer->Add(sample);
-  } while (0);
-*/
-
-// The above pattern is repeated in several macros.  The only elements that
-// vary are the invocation of the Add(sample) vs AddTime(sample), and the choice
-// of which FactoryGet method to use.  The different FactoryGet methods have
-// various argument lists, so the function with its argument list is provided as
-// a macro argument here.  The name is only used in a DCHECK, to assure that
-// callers don't try to vary the name of the histogram (which would tend to be
-// ignored by the one-time initialization of the histogtram_pointer).
-#define STATIC_HISTOGRAM_POINTER_BLOCK(constant_histogram_name, \
-                                       histogram_add_method_invocation, \
-                                       histogram_factory_get_invocation) \
-  do { \
-    static base::subtle::AtomicWord atomic_histogram_pointer = 0; \
-    base::HistogramBase* histogram_pointer( \
-        reinterpret_cast<base::HistogramBase*>( \
-            base::subtle::Acquire_Load(&atomic_histogram_pointer))); \
-    if (!histogram_pointer) { \
-      histogram_pointer = histogram_factory_get_invocation; \
-      base::subtle::Release_Store(&atomic_histogram_pointer, \
-          reinterpret_cast<base::subtle::AtomicWord>(histogram_pointer)); \
-    } \
-    if (DCHECK_IS_ON) \
-      histogram_pointer->CheckName(constant_histogram_name); \
-    histogram_pointer->histogram_add_method_invocation; \
-  } while (0)
-
-
-//------------------------------------------------------------------------------
-// Provide easy general purpose histogram in a macro, just like stats counters.
-// The first four macros use 50 buckets.
-
-#define LOCAL_HISTOGRAM_TIMES(name, sample) LOCAL_HISTOGRAM_CUSTOM_TIMES( \
-    name, sample, base::TimeDelta::FromMilliseconds(1), \
-    base::TimeDelta::FromSeconds(10), 50)
-
-// For folks that need real specific times, use this to select a precise range
-// of times you want plotted, and the number of buckets you want used.
-#define LOCAL_HISTOGRAM_CUSTOM_TIMES(name, sample, min, max, bucket_count) \
-    STATIC_HISTOGRAM_POINTER_BLOCK(name, AddTime(sample), \
-        base::Histogram::FactoryTimeGet(name, min, max, bucket_count, \
-                                        base::HistogramBase::kNoFlags))
-
-#define LOCAL_HISTOGRAM_COUNTS(name, sample) LOCAL_HISTOGRAM_CUSTOM_COUNTS( \
-    name, sample, 1, 1000000, 50)
-
-#define LOCAL_HISTOGRAM_COUNTS_100(name, sample) \
-    LOCAL_HISTOGRAM_CUSTOM_COUNTS(name, sample, 1, 100, 50)
-
-#define LOCAL_HISTOGRAM_COUNTS_10000(name, sample) \
-    LOCAL_HISTOGRAM_CUSTOM_COUNTS(name, sample, 1, 10000, 50)
-
-#define LOCAL_HISTOGRAM_CUSTOM_COUNTS(name, sample, min, max, bucket_count) \
-    STATIC_HISTOGRAM_POINTER_BLOCK(name, Add(sample), \
-        base::Histogram::FactoryGet(name, min, max, bucket_count, \
-                                    base::HistogramBase::kNoFlags))
-
-// This is a helper macro used by other macros and shouldn't be used directly.
-#define HISTOGRAM_ENUMERATION_WITH_FLAG(name, sample, boundary, flag) \
-    STATIC_HISTOGRAM_POINTER_BLOCK(name, Add(sample), \
-        base::LinearHistogram::FactoryGet(name, 1, boundary, boundary + 1, \
-            flag))
-
-#define LOCAL_HISTOGRAM_PERCENTAGE(name, under_one_hundred) \
-    LOCAL_HISTOGRAM_ENUMERATION(name, under_one_hundred, 101)
-
-#define LOCAL_HISTOGRAM_BOOLEAN(name, sample) \
-    STATIC_HISTOGRAM_POINTER_BLOCK(name, AddBoolean(sample), \
-        base::BooleanHistogram::FactoryGet(name, base::Histogram::kNoFlags))
-
-// Support histograming of an enumerated value.  The samples should always be
-// strictly less than |boundary_value| -- this prevents you from running into
-// problems down the line if you add additional buckets to the histogram.  Note
-// also that, despite explicitly setting the minimum bucket value to |1| below,
-// it is fine for enumerated histograms to be 0-indexed -- this is because
-// enumerated histograms should never have underflow.
-#define LOCAL_HISTOGRAM_ENUMERATION(name, sample, boundary_value) \
-    STATIC_HISTOGRAM_POINTER_BLOCK(name, Add(sample), \
-        base::LinearHistogram::FactoryGet(name, 1, boundary_value, \
-            boundary_value + 1, base::HistogramBase::kNoFlags))
-
-// Support histograming of an enumerated value. Samples should be one of the
-// std::vector<int> list provided via |custom_ranges|. See comments above
-// CustomRanges::FactoryGet about the requirement of |custom_ranges|.
-// You can use the helper function CustomHistogram::ArrayToCustomRanges to
-// transform a C-style array of valid sample values to a std::vector<int>.
-#define LOCAL_HISTOGRAM_CUSTOM_ENUMERATION(name, sample, custom_ranges) \
-    STATIC_HISTOGRAM_POINTER_BLOCK(name, Add(sample), \
-        base::CustomHistogram::FactoryGet(name, custom_ranges, \
-                                          base::HistogramBase::kNoFlags))
-
-#define LOCAL_HISTOGRAM_MEMORY_KB(name, sample) LOCAL_HISTOGRAM_CUSTOM_COUNTS( \
-    name, sample, 1000, 500000, 50)
-
-//------------------------------------------------------------------------------
-// The following macros provide typical usage scenarios for callers that wish
-// to record histogram data, and have the data submitted/uploaded via UMA.
-// Not all systems support such UMA, but if they do, the following macros
-// should work with the service.
-
-#define UMA_HISTOGRAM_TIMES(name, sample) UMA_HISTOGRAM_CUSTOM_TIMES( \
-    name, sample, base::TimeDelta::FromMilliseconds(1), \
-    base::TimeDelta::FromSeconds(10), 50)
-
-#define UMA_HISTOGRAM_MEDIUM_TIMES(name, sample) UMA_HISTOGRAM_CUSTOM_TIMES( \
-    name, sample, base::TimeDelta::FromMilliseconds(10), \
-    base::TimeDelta::FromMinutes(3), 50)
-
-// Use this macro when times can routinely be much longer than 10 seconds.
-#define UMA_HISTOGRAM_LONG_TIMES(name, sample) UMA_HISTOGRAM_CUSTOM_TIMES( \
-    name, sample, base::TimeDelta::FromMilliseconds(1), \
-    base::TimeDelta::FromHours(1), 50)
-
-// Use this macro when times can routinely be much longer than 10 seconds and
-// you want 100 buckets.
-#define UMA_HISTOGRAM_LONG_TIMES_100(name, sample) UMA_HISTOGRAM_CUSTOM_TIMES( \
-    name, sample, base::TimeDelta::FromMilliseconds(1), \
-    base::TimeDelta::FromHours(1), 100)
-
-#define UMA_HISTOGRAM_CUSTOM_TIMES(name, sample, min, max, bucket_count) \
-    STATIC_HISTOGRAM_POINTER_BLOCK(name, AddTime(sample), \
-        base::Histogram::FactoryTimeGet(name, min, max, bucket_count, \
-            base::HistogramBase::kUmaTargetedHistogramFlag))
-
-#define UMA_HISTOGRAM_COUNTS(name, sample) UMA_HISTOGRAM_CUSTOM_COUNTS( \
-    name, sample, 1, 1000000, 50)
-
-#define UMA_HISTOGRAM_COUNTS_100(name, sample) UMA_HISTOGRAM_CUSTOM_COUNTS( \
-    name, sample, 1, 100, 50)
-
-#define UMA_HISTOGRAM_COUNTS_10000(name, sample) UMA_HISTOGRAM_CUSTOM_COUNTS( \
-    name, sample, 1, 10000, 50)
-
-#define UMA_HISTOGRAM_CUSTOM_COUNTS(name, sample, min, max, bucket_count) \
-    STATIC_HISTOGRAM_POINTER_BLOCK(name, Add(sample), \
-        base::Histogram::FactoryGet(name, min, max, bucket_count, \
-            base::HistogramBase::kUmaTargetedHistogramFlag))
-
-#define UMA_HISTOGRAM_MEMORY_KB(name, sample) UMA_HISTOGRAM_CUSTOM_COUNTS( \
-    name, sample, 1000, 500000, 50)
-
-#define UMA_HISTOGRAM_MEMORY_MB(name, sample) UMA_HISTOGRAM_CUSTOM_COUNTS( \
-    name, sample, 1, 1000, 50)
-
-#define UMA_HISTOGRAM_PERCENTAGE(name, under_one_hundred) \
-    UMA_HISTOGRAM_ENUMERATION(name, under_one_hundred, 101)
-
-#define UMA_HISTOGRAM_BOOLEAN(name, sample) \
-    STATIC_HISTOGRAM_POINTER_BLOCK(name, AddBoolean(sample), \
-        base::BooleanHistogram::FactoryGet(name, \
-            base::HistogramBase::kUmaTargetedHistogramFlag))
-
-// The samples should always be strictly less than |boundary_value|.  For more
-// details, see the comment for the |LOCAL_HISTOGRAM_ENUMERATION| macro, above.
-#define UMA_HISTOGRAM_ENUMERATION(name, sample, boundary_value) \
-    HISTOGRAM_ENUMERATION_WITH_FLAG(name, sample, boundary_value, \
-        base::HistogramBase::kUmaTargetedHistogramFlag)
-
-// Similar to UMA_HISTOGRAM_ENUMERATION, but used for recording stability
-// histograms.  Use this if recording a histogram that should be part of the
-// initial stability log.
-#define UMA_STABILITY_HISTOGRAM_ENUMERATION(name, sample, boundary_value) \
-    HISTOGRAM_ENUMERATION_WITH_FLAG(name, sample, boundary_value, \
-        base::HistogramBase::kUmaStabilityHistogramFlag)
-
-#define UMA_HISTOGRAM_CUSTOM_ENUMERATION(name, sample, custom_ranges) \
-    STATIC_HISTOGRAM_POINTER_BLOCK(name, Add(sample), \
-        base::CustomHistogram::FactoryGet(name, custom_ranges, \
-            base::HistogramBase::kUmaTargetedHistogramFlag))
-
-//------------------------------------------------------------------------------
-
-class BucketRanges;
-class SampleVector;
-
 class BooleanHistogram;
 class CustomHistogram;
 class Histogram;
 class LinearHistogram;
+class SampleVector;
 
 class BASE_EXPORT Histogram : public HistogramBase {
  public: