Share field trial allocator on zygote-using Linuxes

base/metrics/field_trial.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/metrics/field_trial.h"
 
 #include <algorithm>
 #include <utility>
 
 #include "base/base_switches.h"
 #include "base/build_time.h"
 #include "base/command_line.h"
 #include "base/debug/alias.h"
 #include "base/feature_list.h"
 #include "base/logging.h"
 #include "base/pickle.h"
 #include "base/process/memory.h"
 #include "base/rand_util.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
 
+#if defined(OS_POSIX)
+#include "base/posix/global_descriptors.h"
+#endif
+
 namespace base {
 
 namespace {
 
 // Define a separator character to use when creating a persistent form of an
 // instance.  This is intended for use as a command line argument, passed to a
 // second process to mimic our state (i.e., provide the same group name).
 const char kPersistentStringSeparator = '/';  // Currently a slash.
 
 // Define a marker character to be used as a prefix to a trial name on the
@@ skipping 192 matching lines @@
 #if defined(OS_WIN)
 HANDLE CreateReadOnlyHandle(FieldTrialList::FieldTrialAllocator* allocator) {
   HANDLE src = allocator->shared_memory()->handle().GetHandle();
   ProcessHandle process = GetCurrentProcess();
   DWORD access = SECTION_MAP_READ | SECTION_QUERY;
   HANDLE dst;
   if (!::DuplicateHandle(process, src, process, &dst, access, true, 0))
     return nullptr;
   return dst;
 }
+#elif defined(OS_POSIX) && !defined(OS_NACL)

[Alexei Svitkine (slow), 2016/11/23 17:49:55]

Instead of these #elif chains that are confusing - just use separate ifdefs and
space them out (i.e. empty line between functions.

[lawrencewu, 2016/11/23 18:59:44]

Done.

+int CreateReadOnlyHandle(FieldTrialList::FieldTrialAllocator* allocator) {
+  SharedMemoryHandle new_handle;
+  allocator->shared_memory()->ShareReadOnlyToProcess(GetCurrentProcessHandle(),
+                                                     &new_handle);
+  int fd = SharedMemory::GetFdFromSharedMemoryHandle(new_handle);
+  return fd;

[Alexei Svitkine (slow), 2016/11/23 17:49:55]

Nit: Merge with line above.

[lawrencewu, 2016/11/23 18:59:44]

Done.

+}
 #endif
 
 }  // namespace
 
 // statics
 const int FieldTrial::kNotFinalized = -1;
 const int FieldTrial::kDefaultGroupNumber = 0;
 bool FieldTrial::enable_benchmarking_ = false;
 
 int FieldTrialList::kNoExpirationYear = 0;
@@ skipping 484 matching lines @@
   }
   return true;
 }
 
 // static
 void FieldTrialList::CreateTrialsFromCommandLine(
     const CommandLine& cmd_line,
     const char* field_trial_handle_switch) {
   global_->create_trials_from_command_line_called_ = true;
 
-#if defined(OS_WIN) && !defined(OS_NACL)
   if (cmd_line.HasSwitch(field_trial_handle_switch)) {
     std::string arg = cmd_line.GetSwitchValueASCII(field_trial_handle_switch);
-    int field_trial_handle = std::stoi(arg);
-    HANDLE handle = reinterpret_cast<HANDLE>(field_trial_handle);
-    bool result = CreateTrialsFromWindowsHandle(handle);
+#if defined(OS_WIN)
+    bool result = CreateTrialsFromWindowsSwitch(arg);
     DCHECK(result);
+#elif defined(OS_POSIX) && !defined(OS_NACL)
+    bool result = CreateTrialsFromPosixSwitch(arg);
+    DCHECK(result);
+#endif
   }
-#endif
 
   if (cmd_line.HasSwitch(switches::kForceFieldTrials)) {
     bool result = FieldTrialList::CreateTrialsFromString(
         cmd_line.GetSwitchValueASCII(switches::kForceFieldTrials),
         std::set<std::string>());
     DCHECK(result);
   }
 }
 
 #if defined(OS_WIN)
 // static
 void FieldTrialList::AppendFieldTrialHandleIfNeeded(
     HandlesToInheritVector* handles) {
   if (!global_)
     return;
   if (kUseSharedMemoryForFieldTrials) {
     InstantiateFieldTrialAllocatorIfNeeded();
     if (global_->readonly_allocator_handle_)
       handles->push_back(global_->readonly_allocator_handle_);
   }
 }
+#elif defined(OS_POSIX) && !defined(OS_NACL)
+// static
+int FieldTrialList::FieldTrialHandle() {
+  if (!global_)
+    return -1;
+  if (kUseSharedMemoryForFieldTrials) {
+    InstantiateFieldTrialAllocatorIfNeeded();
+    if (global_->readonly_allocator_handle_ != -1)
+      return global_->readonly_allocator_handle_;
+  }
+  return -1;
+}
 #endif
 
 // static
 void FieldTrialList::CopyFieldTrialStateToFlags(
     const char* field_trial_handle_switch,
     CommandLine* cmd_line) {
   // TODO(lawrencewu): Ideally, having the global would be guaranteed. However,
   // content browser tests currently don't create a FieldTrialList because they
   // don't run ChromeBrowserMainParts code where it's done for Chrome.
   if (!global_)
@@ skipping 15 matching lines @@
     // int (uintptr_t, to be exact), stringify the int, and pass it as a
     // command-line flag. The child process will do the reverse conversions to
     // retrieve the handle. See http://stackoverflow.com/a/153077
     auto uintptr_handle =
         reinterpret_cast<uintptr_t>(global_->readonly_allocator_handle_);
     std::string field_trial_handle = std::to_string(uintptr_handle);
     cmd_line->AppendSwitchASCII(field_trial_handle_switch, field_trial_handle);
     global_->field_trial_allocator_->UpdateTrackingHistograms();
     return;
   }
+#elif defined(OS_POSIX) && !defined(OS_NACL)
+  // Use shared memory to pass the state if the feature is enabled, otherwise
+  // fallback to passing it via the command line as a string.
+  if (kUseSharedMemoryForFieldTrials) {
+    InstantiateFieldTrialAllocatorIfNeeded();
+    // If the readonly handle didn't get duplicated properly, then fallback to
+    // original behavior.
+    if (global_->readonly_allocator_handle_ == -1) {
+      AddForceFieldTrialsFlag(cmd_line);
+      return;
+    }
+
+    std::string field_trial_handle =
+        std::to_string(global_->readonly_allocator_handle_);
+    cmd_line->AppendSwitchASCII(field_trial_handle_switch, field_trial_handle);
+    global_->field_trial_allocator_->UpdateTrackingHistograms();
+    return;
+  }
 #endif
 
   AddForceFieldTrialsFlag(cmd_line);
 }
 
 // static
 FieldTrial* FieldTrialList::CreateFieldTrial(
     const std::string& name,
     const std::string& group_name) {
   DCHECK(global_);
@@ skipping 70 matching lines @@
 // static
 size_t FieldTrialList::GetFieldTrialCount() {
   if (!global_)
     return 0;
   AutoLock auto_lock(global_->lock_);
   return global_->registered_.size();
 }
 
 #if defined(OS_WIN)
 // static
-bool FieldTrialList::CreateTrialsFromWindowsHandle(HANDLE handle) {
+bool FieldTrialList::CreateTrialsFromWindowsSwitch(std::string cli_switch) {
+  int field_trial_handle = std::stoi(cli_switch);
+  HANDLE handle = reinterpret_cast<HANDLE>(field_trial_handle);
   SharedMemoryHandle shm_handle(handle, GetCurrentProcId());
+  return FieldTrialList::CreateTrialsFromSharedMemoryHandle(shm_handle);
+}
+#elif defined(OS_POSIX) && !defined(OS_NACL)
+// static
+bool FieldTrialList::CreateTrialsFromPosixSwitch(std::string cli_switch) {
+  int fd_key = std::stoi(cli_switch);
+  int fd = GlobalDescriptors::GetInstance()->Get(fd_key);
+  SharedMemoryHandle shm_handle(fd, true);
+  return FieldTrialList::CreateTrialsFromSharedMemoryHandle(shm_handle);
+}
+#endif
 
+#if !defined(OS_NACL)
+// static
+bool FieldTrialList::CreateTrialsFromSharedMemoryHandle(
+    SharedMemoryHandle shm_handle) {
   // shm gets deleted when it gets out of scope, but that's OK because we need
   // it only for the duration of this method.
   std::unique_ptr<SharedMemory> shm(new SharedMemory(shm_handle, true));
   if (!shm.get()->Map(kFieldTrialAllocationSize))
     TerminateBecauseOutOfMemory(kFieldTrialAllocationSize);
 
   return FieldTrialList::CreateTrialsFromSharedMemory(std::move(shm));
 }
 #endif
 
@@ skipping 69 matching lines @@
 #if !defined(OS_NACL)
 // static
 void FieldTrialList::InstantiateFieldTrialAllocatorIfNeeded() {
   if (!global_)
     return;
   AutoLock auto_lock(global_->lock_);
   // Create the allocator if not already created and add all existing trials.
   if (global_->field_trial_allocator_ != nullptr)
     return;
 
+  SharedMemoryCreateOptions options;
+  options.size = kFieldTrialAllocationSize;
+  options.share_read_only = true;
+
   std::unique_ptr<SharedMemory> shm(new SharedMemory());
-  if (!shm->CreateAndMapAnonymous(kFieldTrialAllocationSize))
+  if (!shm->Create(options))
+    TerminateBecauseOutOfMemory(kFieldTrialAllocationSize);
+
+  if (!shm->Map(kFieldTrialAllocationSize))
     TerminateBecauseOutOfMemory(kFieldTrialAllocationSize);
 
   global_->field_trial_allocator_.reset(
       new FieldTrialAllocator(std::move(shm), 0, kAllocatorName, false));
   global_->field_trial_allocator_->CreateTrackingHistograms(kAllocatorName);
 
   // Add all existing field trials.
   for (const auto& registered : global_->registered_) {
     AddToAllocatorWhileLocked(registered.second);
   }
 
-#if defined(OS_WIN)
+#if defined(OS_WIN) || defined(OS_POSIX)
   // Set |readonly_allocator_handle_| so we can pass it to be inherited and
   // via the command line.
   global_->readonly_allocator_handle_ =
       CreateReadOnlyHandle(global_->field_trial_allocator_.get());
 #endif
 }
 #endif
 
 // static
 void FieldTrialList::AddToAllocatorWhileLocked(FieldTrial* field_trial) {
@@ skipping 94 matching lines @@
     return;
   }
   AutoLock auto_lock(global_->lock_);
   CHECK(!global_->PreLockedFind(trial->trial_name())) << trial->trial_name();
   trial->AddRef();
   trial->SetTrialRegistered();
   global_->registered_[trial->trial_name()] = trial;
 }
 
 }  // namespace base