Use persistent memory for receiving metrics from sub-processes.

content/browser/browser_child_process_host_impl.cc

Index: content/browser/browser_child_process_host_impl.cc
diff --git a/content/browser/browser_child_process_host_impl.cc b/content/browser/browser_child_process_host_impl.cc
index afc52015320fecafb9abc463abf4a979e56945f4..c5f61aba6b38953d91fcdbaa7818bf06ea3a8059 100644
--- a/content/browser/browser_child_process_host_impl.cc
+++ b/content/browser/browser_child_process_host_impl.cc
@@ -15,6 +15,8 @@
 #include "base/macros.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
+#include "base/metrics/persistent_histogram_allocator.h"
+#include "base/metrics/persistent_memory_allocator.h"
 #include "base/stl_util.h"
 #include "base/strings/string_util.h"
 #include "base/synchronization/waitable_event.h"
@@ -84,15 +86,15 @@ BrowserChildProcessHost* BrowserChildProcessHost::Create(
     content::ProcessType process_type,
     BrowserChildProcessHostDelegate* delegate) {
   return new BrowserChildProcessHostImpl(
-      process_type, delegate, mojo::edk::GenerateRandomToken());
+      process_type, delegate, mojo::edk::GenerateRandomToken(), 0, nullptr);
 }
 
 BrowserChildProcessHost* BrowserChildProcessHost::Create(
     content::ProcessType process_type,
     BrowserChildProcessHostDelegate* delegate,
     const std::string& mojo_child_token) {
-  return new BrowserChildProcessHostImpl(
-      process_type, delegate, mojo_child_token);
+  return new BrowserChildProcessHostImpl(process_type, delegate,
+                                         mojo_child_token, 0, nullptr);
 }
 
 BrowserChildProcessHost* BrowserChildProcessHost::FromID(int child_process_id) {
@@ -135,7 +137,9 @@ void BrowserChildProcessHostImpl::RemoveObserver(
 BrowserChildProcessHostImpl::BrowserChildProcessHostImpl(
     content::ProcessType process_type,
     BrowserChildProcessHostDelegate* delegate,
-    const std::string& mojo_child_token)
+    const std::string& mojo_child_token,
+    size_t shared_metrics_memory_size,
+    base::StringPiece shared_metrics_name)
     : data_(process_type),
       delegate_(delegate),
       mojo_child_token_(mojo_child_token),
@@ -168,6 +172,16 @@ BrowserChildProcessHostImpl::BrowserChildProcessHostImpl(
   GetContentClient()->browser()->BrowserChildProcessHostCreated(this);
 
   power_monitor_message_broadcaster_.Init();
+
+  // Create a persistent memory segment for subprocess histograms only if
+  // they're active in the browser.
+  if (shared_metrics_memory_size > 0 && base::GlobalHistogramAllocator::Get()) {
+    std::unique_ptr<base::SharedMemory> shm(new base::SharedMemory());
+    shm->CreateAndMapAnonymous(shared_metrics_memory_size);
+    metrics_allocator_.reset(new base::SharedPersistentMemoryAllocator(
+        std::move(shm), static_cast<uint64_t>(data_.id), shared_metrics_name,
+        /*readonly=*/false));
+  }
 }
 
 BrowserChildProcessHostImpl::~BrowserChildProcessHostImpl() {
@@ -268,6 +282,11 @@ const base::Process& BrowserChildProcessHostImpl::GetProcess() const {
   return child_process_->GetProcess();
 }
 
+std::unique_ptr<base::SharedPersistentMemoryAllocator>
+BrowserChildProcessHostImpl::TakeMetricsAllocator() {
+  return std::move(metrics_allocator_);
+}
+
 void BrowserChildProcessHostImpl::SetName(const base::string16& name) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   data_.name = name;
@@ -335,6 +354,7 @@ void BrowserChildProcessHostImpl::OnChannelConnected(int32_t peer_pid) {
   delegate_->OnChannelConnected(peer_pid);
 
   if (IsProcessLaunched()) {
+    ShareMetricsAllocatorToProcess();
     BrowserThread::PostTask(BrowserThread::UI, FROM_HERE,
                             base::Bind(&NotifyProcessLaunchedAndConnected,
                                        data_));
@@ -436,6 +456,16 @@ bool BrowserChildProcessHostImpl::Send(IPC::Message* message) {
   return child_process_host_->Send(message);
 }
 
+void BrowserChildProcessHostImpl::ShareMetricsAllocatorToProcess() {
+  if (metrics_allocator_) {
+    base::SharedMemoryHandle shm_handle;
+    metrics_allocator_->shared_memory()->ShareToProcess(data_.handle,
+                                                        &shm_handle);
+    Send(new ChildProcessMsg_SetHistogramMemory(
+        shm_handle, metrics_allocator_->shared_memory()->mapped_size()));
+  }
+}
+
 void BrowserChildProcessHostImpl::OnProcessLaunchFailed(int error_code) {
   delegate_->OnProcessLaunchFailed(error_code);
   notify_child_disconnected_ = false;
@@ -462,6 +492,7 @@ void BrowserChildProcessHostImpl::OnProcessLaunched() {
   delegate_->OnProcessLaunched();
 
   if (is_channel_connected_) {
+    ShareMetricsAllocatorToProcess();
     BrowserThread::PostTask(BrowserThread::UI, FROM_HERE,
                             base::Bind(&NotifyProcessLaunchedAndConnected,
                                        data_));