Index: base/metrics/field_trial.cc |
diff --git a/base/metrics/field_trial.cc b/base/metrics/field_trial.cc |
index 4f3e0c76fcd58c606f3b98f90718f8dc63538d5f..2f993402c548bca98d24de03f32e108d5f300496 100644 |
--- a/base/metrics/field_trial.cc |
+++ b/base/metrics/field_trial.cc |
@@ -35,10 +35,46 @@ const char kActivationMarker = '*'; |
// for now while the implementation is fleshed out (e.g. data format, single |
// shared memory segment). See https://codereview.chromium.org/2365273004/ and |
// crbug.com/653874 |
-#if defined(OS_WIN) |
const bool kUseSharedMemoryForFieldTrials = false; |
+ |
+// Allocator used to instantiate field trial in child processes. In the |
+// future, we may want to move this to a more generic place if we want to |
+// start passing more data other than field trials. |
+base::SharedPersistentMemoryAllocator* g_field_trial_allocator = nullptr; |
+#if defined(OS_WIN) |
+HANDLE g_readonly_allocator_handle = 0; |
#endif |
+// Constants for the field trial allocator. |
+const char kAllocatorName[] = "FieldTrialAllocator"; |
+const uint32_t kFieldTrialType = 0xABA17E13 + 1; // SHA1(FieldTrialEntry) v1 |
+ |
+// We create one FieldTrialEntry struct per field trial in shared memory (via |
+// g_field_trial_allocator). It contains whether or not it's activated, and the |
+// offset from the start of the allocated memory to the group name. We don't |
+// need the offset into the trial name because that's always a fixed position |
+// from the start of the struct. Two strings will be appended to the end of this |
+// structure in allocated memory, so the result will look like this: |
+// --------------------------------- |
+// | fte | trial_name | group_name | |
+// --------------------------------- |
+struct FieldTrialEntry { |
+ bool activated; |
+ uint32_t group_name_offset; |
+ |
+ const char* GetTrialName() const { |
+ const char* src = |
+ reinterpret_cast<char*>(const_cast<FieldTrialEntry*>(this)); |
+ return src + sizeof(FieldTrialEntry); |
+ } |
+ |
+ const char* GetGroupName() const { |
+ const char* src = |
+ reinterpret_cast<char*>(const_cast<FieldTrialEntry*>(this)); |
+ return src + this->group_name_offset; |
+ } |
+}; |
+ |
// Created a time value based on |year|, |month| and |day_of_month| parameters. |
Time CreateTimeFromParams(int year, int month, int day_of_month) { |
DCHECK_GT(year, 1970); |
@@ -129,6 +165,7 @@ bool ParseFieldTrialsString(const std::string& trials_string, |
// statics |
const int FieldTrial::kNotFinalized = -1; |
const int FieldTrial::kDefaultGroupNumber = 0; |
+const int kFieldTrialAllocationSize = 4 << 10; // 4 KiB = one page |
bool FieldTrial::enable_benchmarking_ = false; |
int FieldTrialList::kNoExpirationYear = 0; |
@@ -586,14 +623,12 @@ void FieldTrialList::CreateTrialsFromCommandLine( |
base::SharedMemoryHandle(handle, base::GetCurrentProcId()); |
// Gets deleted when it gets out of scope, but that's OK because we need it |
- // only for the duration of this call currently anyway. |
- base::SharedMemory shared_memory(shm_handle, false); |
- shared_memory.Map(field_trial_length); |
+ // only for the duration of this method. |
+ std::unique_ptr<base::SharedMemory> shm( |
+ new base::SharedMemory(shm_handle, true)); |
+ shm.get()->Map(field_trial_length); |
bcwhite
2016/10/20 21:14:06
Map() will return false if it fails which can happ
lawrencewu
2016/10/21 16:41:58
Done.
|
- char* field_trial_state = static_cast<char*>(shared_memory.memory()); |
- bool result = FieldTrialList::CreateTrialsFromString( |
- std::string(field_trial_state), std::set<std::string>()); |
- DCHECK(result); |
+ FieldTrialList::CreateTrialsFromSharedMemory(std::move(shm)); |
return; |
} |
#endif |
@@ -606,37 +641,78 @@ void FieldTrialList::CreateTrialsFromCommandLine( |
} |
} |
+#if defined(OS_WIN) |
+// static |
+void FieldTrialList::AppendFieldTrialHandleIfNeeded( |
+ base::HandlesToInheritVector* handles) { |
+ FieldTrialList::InstantiateFieldTrialAllocatorIfNeeded(); |
+ |
+ // Need to get a new, read-only handle to share to the child. |
+ handles->push_back(g_readonly_allocator_handle); |
+} |
+#endif |
+ |
// static |
-std::unique_ptr<base::SharedMemory> FieldTrialList::CopyFieldTrialStateToFlags( |
+void FieldTrialList::CreateTrialsFromSharedMemory( |
+ std::unique_ptr<base::SharedMemory> shm) { |
+ const base::SharedPersistentMemoryAllocator shalloc(std::move(shm), 0, |
+ kAllocatorName, true); |
+ base::PersistentMemoryAllocator::Iterator iter(&shalloc); |
+ |
+ base::SharedPersistentMemoryAllocator::Reference ref; |
+ while ((ref = iter.GetNextOfType(kFieldTrialType)) != |
+ base::SharedPersistentMemoryAllocator::kReferenceNull) { |
+ const FieldTrialEntry* entry = |
+ shalloc.GetAsObject<const FieldTrialEntry>(ref, kFieldTrialType); |
+ FieldTrial* trial = |
+ CreateFieldTrial(entry->GetTrialName(), entry->GetGroupName()); |
+ |
+ if (entry->activated) { |
+ // Call |group()| to mark the trial as "used" and notify observers, if |
+ // any. This is useful to ensure that field trials created in child |
+ // processes are properly reported in crash reports. |
+ trial->group(); |
+ } |
+ } |
+} |
+ |
+// static |
+void FieldTrialList::CopyFieldTrialStateToFlags( |
const char* field_trial_handle_switch, |
base::CommandLine* cmd_line) { |
+#if defined(OS_WIN) |
+ // 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) { |
+ FieldTrialList::InstantiateFieldTrialAllocatorIfNeeded(); |
+ // HANDLE is just typedef'd to void *. We basically cast the handle into an |
+ // 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>(g_readonly_allocator_handle); |
+ size_t field_trial_length = |
+ g_field_trial_allocator->shared_memory()->mapped_size(); |
bcwhite
2016/10/20 21:14:06
Instead of UpdateTrackingHistograms you could also
lawrencewu
2016/10/23 20:01:56
Ack, will do later.
|
+ std::string field_trial_handle = std::to_string(uintptr_handle) + "," + |
+ std::to_string(field_trial_length); |
+ |
+ cmd_line->AppendSwitchASCII(field_trial_handle_switch, field_trial_handle); |
+ return; |
+ } |
+#endif |
+ |
std::string field_trial_states; |
base::FieldTrialList::AllStatesToString(&field_trial_states); |
if (!field_trial_states.empty()) { |
-// 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 defined(OS_WIN) |
- if (kUseSharedMemoryForFieldTrials) { |
- std::unique_ptr<base::SharedMemory> shm(new base::SharedMemory()); |
- size_t length = field_trial_states.size() + 1; |
- shm->CreateAndMapAnonymous(length); |
- memcpy(shm->memory(), field_trial_states.c_str(), length); |
- |
- // HANDLE is just typedef'd to void * |
- auto uintptr_handle = |
- reinterpret_cast<std::uintptr_t>(shm->handle().GetHandle()); |
- std::string field_trial_handle = |
- std::to_string(uintptr_handle) + "," + std::to_string(length); |
- |
- cmd_line->AppendSwitchASCII(field_trial_handle_switch, |
- field_trial_handle); |
- return shm; |
- } |
-#endif |
cmd_line->AppendSwitchASCII(switches::kForceFieldTrials, |
field_trial_states); |
} |
- return std::unique_ptr<base::SharedMemory>(nullptr); |
+} |
+ |
+// static |
+base::SharedPersistentMemoryAllocator* |
+FieldTrialList::GetFieldTrialAllocatorForTesting() { |
+ return g_field_trial_allocator; |
} |
// static |
@@ -694,12 +770,87 @@ void FieldTrialList::NotifyFieldTrialGroupSelection(FieldTrial* field_trial) { |
if (!field_trial->enable_field_trial_) |
return; |
+ if (kUseSharedMemoryForFieldTrials) { |
+ FieldTrialList::UpdateFieldTrialAllocator(field_trial); |
+ } |
+ |
global_->observer_list_->Notify( |
FROM_HERE, &FieldTrialList::Observer::OnFieldTrialGroupFinalized, |
field_trial->trial_name(), field_trial->group_name_internal()); |
} |
// static |
+void FieldTrialList::InstantiateFieldTrialAllocatorIfNeeded() { |
+ AutoLock auto_lock(global_->lock_); |
+ // Create the allocator if not already created and add all existing trials. |
+ if (g_field_trial_allocator == nullptr) { |
+ std::unique_ptr<base::SharedMemory> shm(new base::SharedMemory()); |
+ shm->CreateAndMapAnonymous(kFieldTrialAllocationSize); |
+ |
+ // TODO(lawrencewu): call UpdateTrackingHistograms() when all field trials |
+ // have been registered (perhaps in the destructor?) |
+ g_field_trial_allocator = new base::SharedPersistentMemoryAllocator( |
+ std::move(shm), 0, kAllocatorName, false); |
+ g_field_trial_allocator->CreateTrackingHistograms(kAllocatorName); |
+ |
+ // Add all existing field trials. |
+ for (const auto& registered : global_->registered_) { |
+ FieldTrialList::UpdateFieldTrialAllocator(registered.second); |
+ } |
+ |
+#if defined(OS_WIN) |
+ // Duplicate and set |g_readonly_allocator_handle| so we can pass it to be |
+ // inherited and via the command line. |
+ HANDLE src = g_field_trial_allocator->shared_memory()->handle().GetHandle(); |
+ ProcessHandle process = GetCurrentProcess(); |
+ DWORD access = SECTION_MAP_READ | SECTION_QUERY; |
+ ::DuplicateHandle(process, src, process, &g_readonly_allocator_handle, |
+ access, true, 0); |
+#endif |
+ } |
+} |
+ |
+// static |
+void FieldTrialList::UpdateFieldTrialAllocator(FieldTrial* field_trial) { |
+ // Don't do anything if the allocator hasn't been instantiated yet. |
+ if (g_field_trial_allocator == nullptr) |
bcwhite
2016/10/21 13:48:29
Since we've established that there could be parall
lawrencewu
2016/10/23 20:01:56
Done.
|
+ return; |
+ |
+ // We allocate just enough memory to fit the FTE struct, trial name, and group |
+ // name. If there's no more memory available, quit early. |
+ FieldTrial::State trial_state; |
+ field_trial->GetState(&trial_state); |
+ |
+ std::string trial_name; |
+ trial_state.trial_name.CopyToString(&trial_name); |
+ size_t trial_name_size = trial_name.size() + 1; |
+ |
+ std::string group_name; |
+ trial_state.group_name.CopyToString(&group_name); |
+ size_t group_name_size = group_name.size() + 1; |
+ |
+ uint32_t trial_name_offset = sizeof(FieldTrialEntry); |
+ uint32_t group_name_offset = trial_name_offset + trial_name_size; |
+ size_t size = sizeof(FieldTrialEntry) + trial_name_size + group_name_size; |
+ |
+ base::SharedPersistentMemoryAllocator::Reference ref = |
+ g_field_trial_allocator->Allocate(size, kFieldTrialType); |
+ if (ref == base::SharedPersistentMemoryAllocator::kReferenceNull) |
+ return; |
+ |
+ FieldTrialEntry* dst = g_field_trial_allocator->GetAsObject<FieldTrialEntry>( |
+ ref, kFieldTrialType); |
+ FieldTrialEntry entry = {trial_state.activated, group_name_offset}; |
+ *dst = entry; |
+ memcpy(reinterpret_cast<char*>(dst) + trial_name_offset, trial_name.c_str(), |
+ trial_name_size); |
+ memcpy(reinterpret_cast<char*>(dst) + group_name_offset, group_name.c_str(), |
+ group_name_size); |
+ |
+ g_field_trial_allocator->MakeIterable(ref); |
+} |
+ |
+// static |
size_t FieldTrialList::GetFieldTrialCount() { |
if (!global_) |
return 0; |