Add UMA to track the number of live URLRequests.

UMA data shows that there can be a large number of active
HttpStreamRequests at a given time. The number reported by
ResourceDispatcherHostImpl doesn't account for the large number of
HttpStreamRequests. This CL adds a histogram to track the number of
active URLRequests, so we can know whether the cause for the large
number of HttpStreamRequests is internal or external to the network
stack.

BUG=711721

Review-Url: https://codereview.chromium.org/2837313002
Cr-Commit-Position: refs/heads/master@{#467332}

net/log/net_log_util.cc

@@ -515,7 +515,7 @@ NET_EXPORT void CreateNetLogEntriesForActiveObjects(
     DCHECK(context->CalledOnValidThread());
     // Contexts should all be using the same NetLog.
     DCHECK_EQ((*contexts.begin())->net_log(), context->net_log());
-    for (auto* request : *context->url_requests()) {
+    for (auto* request : context->url_requests()) {
       requests.push_back(request);
     }
   }

net/url_request/url_request.cc

@@ -186,8 +186,7 @@ URLRequest::~URLRequest() {
   // on UserData associated with |this| and poke at it during teardown.
   job_.reset();
 
-  DCHECK_EQ(1u, context_->url_requests()->count(this));
-  context_->url_requests()->erase(this);
+  context_->RemoveURLRequest(this);
 
   int net_error = OK;
   // Log error only on failure, not cancellation, as even successful requests
@@ -585,7 +584,7 @@ URLRequest::URLRequest(const GURL& url,
   // Sanity check out environment.
   DCHECK(base::ThreadTaskRunnerHandle::IsSet());
 
-  context->url_requests()->insert(this);
+  context->InsertURLRequest(this);
   net_log_.BeginEvent(
       NetLogEventType::REQUEST_ALIVE,
       base::Bind(&NetLogURLRequestConstructorCallback, &url, priority_));

net/url_request/url_request_context.cc

@@ -9,6 +9,7 @@
 #include "base/compiler_specific.h"
 #include "base/debug/alias.h"
 #include "base/memory/ptr_util.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/threading/thread_task_runner_handle.h"
@@ -48,10 +49,10 @@ URLRequestContext::URLRequestContext()
       sdch_manager_(nullptr),
       network_quality_estimator_(nullptr),
       reporting_service_(nullptr),
-      url_requests_(new std::set<const URLRequest*>),
       enable_brotli_(false),
       check_cleartext_permitted_(false),
-      name_(nullptr) {
+      name_(nullptr),
+      largest_outstanding_requests_count_seen_(0) {
   base::trace_event::MemoryDumpManager::GetInstance()->RegisterDumpProvider(
       this, "URLRequestContext", base::ThreadTaskRunnerHandle::Get());
 }
@@ -122,13 +123,27 @@ void URLRequestContext::set_cookie_store(CookieStore* cookie_store) {
   cookie_store_ = cookie_store;
 }
 
+void URLRequestContext::InsertURLRequest(const URLRequest* request) const {
+  url_requests_.insert(request);
+  if (url_requests_.size() > largest_outstanding_requests_count_seen_) {
+    largest_outstanding_requests_count_seen_ = url_requests_.size();
+    UMA_HISTOGRAM_COUNTS_1M("Net.URLRequestContext.OutstandingRequests",
+                            largest_outstanding_requests_count_seen_);
+  }
+}
+
+void URLRequestContext::RemoveURLRequest(const URLRequest* request) const {
+  DCHECK_EQ(1u, url_requests_.count(request));
+  url_requests_.erase(request);
+}
+
 void URLRequestContext::AssertNoURLRequests() const {
-  int num_requests = url_requests_->size();
+  int num_requests = url_requests_.size();
   if (num_requests != 0) {
     // We're leaking URLRequests :( Dump the URL of the first one and record how
     // many we leaked so we have an idea of how bad it is.
     char url_buf[128];
-    const URLRequest* request = *url_requests_->begin();
+    const URLRequest* request = *url_requests_.begin();
     base::strlcpy(url_buf, request->url().spec().c_str(), arraysize(url_buf));
     int load_flags = request->load_flags();
     base::debug::Alias(url_buf);
@@ -154,7 +169,7 @@ bool URLRequestContext::OnMemoryDump(
       pmd->CreateAllocatorDump(dump_name);
   dump->AddScalar(base::trace_event::MemoryAllocatorDump::kNameObjectCount,
                   base::trace_event::MemoryAllocatorDump::kUnitsObjects,
-                  url_requests_->size());
+                  url_requests_.size());
   HttpTransactionFactory* transaction_factory = http_transaction_factory();
   if (transaction_factory) {
     HttpNetworkSession* network_session = transaction_factory->GetSession();

net/url_request/url_request_context.h

@@ -221,10 +221,14 @@ class NET_EXPORT URLRequestContext
 
   // Gets the URLRequest objects that hold a reference to this
   // URLRequestContext.
-  std::set<const URLRequest*>* url_requests() const {
-    return url_requests_.get();
+  const std::set<const URLRequest*>& url_requests() const {
+    return url_requests_;
   }
 
+  void InsertURLRequest(const URLRequest* request) const;
+
+  void RemoveURLRequest(const URLRequest* request) const;
+
   // CHECKs that no URLRequests using this context remain. Subclasses should
   // additionally call AssertNoURLRequests() within their own destructor,
   // prior to implicit destruction of subclass-owned state.
@@ -312,7 +316,7 @@ class NET_EXPORT URLRequestContext
   // be added to CopyFrom.
   // ---------------------------------------------------------------------------
 
-  std::unique_ptr<std::set<const URLRequest*>> url_requests_;
+  mutable std::set<const URLRequest*> url_requests_;
 
   // Enables Brotli Content-Encoding support.
   bool enable_brotli_;
@@ -325,6 +329,10 @@ class NET_EXPORT URLRequestContext
   // to be unique.
   const char* name_;
 
+  // The largest number of outstanding URLRequests that have been created by
+  // |this| and are not yet destroyed. This doesn't need to be in CopyFrom.
+  mutable size_t largest_outstanding_requests_count_seen_;
+
   DISALLOW_COPY_AND_ASSIGN(URLRequestContext);
 };
 

tools/metrics/histograms/histograms.xml

@@ -39229,6 +39229,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>True if a URLRequest's referrer is empty or valid when set.</summary>
 </histogram>
 
+<histogram name="Net.URLRequestContext.OutstandingRequests" units="count">
+  <owner>xunjieli@chromium.org</owner>
+  <summary>
+    Indicates the number of URLRequests that are handed out by a
+    URLRequestContext and are not yet destroyed.
+  </summary>
+</histogram>
+
 <histogram name="Net.ValidDNSName" enum="Boolean">
   <owner>palmer@chromium.org</owner>
   <summary>