Add DCHECK to detect misuse of HISTOGRAM interface.

The interface (for perf reasons) snapshots the histogram
name, and reuses it in future calls. As a result, any attempt
to modulate (change) the name between call is ignored.

This change uses a DCHECK to detect such abuse.

BUG=43377
BUG=43375
r=vandebo
Review URL: http://codereview.chromium.org/2019001

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@46726 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 16 insertions, 8 deletions

diff --git a/net/socket/client_socket_handle.cc b/net/socket/client_socket_handle.cc
index 6e3a587..87212b1 100644
--- a/net/socket/client_socket_handle.cc
+++ b/net/socket/client_socket_handle.cc
@@ -75,32 +75,40 @@ void ClientSocketHandle::HandleInitCompletion(int result) {
   }
   setup_time_ = base::TimeTicks::Now() - init_time_;
 
-  std::string metric = "Net." + pool_->name() + "SocketType";
+  // TODO(vandebo): bug 43375: The strings passed to HISTOGRAM macros should NOT
+  // vary, as the macro snapshots the name into a static.  I've temporarilly
+  // made this code use statics so that the HISTOGRAM macro will not DCHECK (and
+  // this also makes the current semantics a tiny bit more clear).
+  static std::string metric = "Net." + pool_->name() + "SocketType";
   UMA_HISTOGRAM_ENUMERATION(metric, reuse_type(), NUM_TYPES);
   switch (reuse_type()) {
-    case ClientSocketHandle::UNUSED:
-      metric = "Net." + pool_->name() + "SocketRequestTime";
+    case ClientSocketHandle::UNUSED: {
+      static std::string metric = "Net." + pool_->name() + "SocketRequestTime";
       UMA_HISTOGRAM_CLIPPED_TIMES(metric, setup_time(),
                                   base::TimeDelta::FromMilliseconds(1),
                                   base::TimeDelta::FromMinutes(10), 100);
       break;
-    case ClientSocketHandle::UNUSED_IDLE:
-      metric = "Net." + pool_->name() +
+    }
+    case ClientSocketHandle::UNUSED_IDLE: {
+      static std::string metric = "Net." + pool_->name() +
           "SocketIdleTimeBeforeNextUse_UnusedSocket";
       UMA_HISTOGRAM_CUSTOM_TIMES(metric, idle_time(),
                                  base::TimeDelta::FromMilliseconds(1),
                                  base::TimeDelta::FromMinutes(6), 100);
       break;
-    case ClientSocketHandle::REUSED_IDLE:
-      metric = "Net." + pool_->name() +
+    }
+    case ClientSocketHandle::REUSED_IDLE: {
+      static std::string metric = "Net." + pool_->name() +
           "SocketIdleTimeBeforeNextUse_ReusedSocket";
       UMA_HISTOGRAM_CUSTOM_TIMES(metric, idle_time(),
                                  base::TimeDelta::FromMilliseconds(1),
                                  base::TimeDelta::FromMinutes(6), 100);
       break;
-    default:
+    }
+    default: {
       NOTREACHED();
       break;
+    }
   }
 }