Add analyzer support for multiple processes.

base/debug/activity_tracker.cc

 // Copyright 2016 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/debug/activity_tracker.h"
 
 #include <algorithm>
 #include <limits>
 #include <utility>
 
@@ skipping 302 matching lines @@
 ActivityUserData::ValueInfo::ValueInfo(ValueInfo&&) = default;
 ActivityUserData::ValueInfo::~ValueInfo() {}
 ActivityUserData::MemoryHeader::MemoryHeader() {}
 ActivityUserData::MemoryHeader::~MemoryHeader() {}
 ActivityUserData::FieldHeader::FieldHeader() {}
 ActivityUserData::FieldHeader::~FieldHeader() {}
 
 ActivityUserData::ActivityUserData(void* memory, size_t size)
     : memory_(reinterpret_cast<char*>(memory)),
       available_(RoundDownToAlignment(size, kMemoryAlignment)),
-      header_(reinterpret_cast<MemoryHeader*>(memory)) {
+      header_(reinterpret_cast<MemoryHeader*>(memory)),
+      orig_data_id(0),
+      orig_process_id(0),
+      orig_create_stamp(0) {
   // It's possible that no user data is being stored.
   if (!memory_)
     return;
 
   static_assert(0 == sizeof(MemoryHeader) % kMemoryAlignment, "invalid header");
   DCHECK_LT(sizeof(MemoryHeader), available_);
   if (header_->owner.data_id.load(std::memory_order_acquire) == 0)
     header_->owner.Release_Initialize();
   memory_ += sizeof(MemoryHeader);
   available_ -= sizeof(MemoryHeader);
 
+  // Make a copy of identifying information for later comparison.
+  *const_cast<uint32_t*>(&orig_data_id) =
+      header_->owner.data_id.load(std::memory_order_acquire);
+  *const_cast<int64_t*>(&orig_process_id) = header_->owner.process_id;
+  *const_cast<int64_t*>(&orig_create_stamp) = header_->owner.create_stamp;
+
   // If there is already data present, load that. This allows the same class
   // to be used for analysis through snapshots.
   ImportExistingData();
 }
 
 ActivityUserData::~ActivityUserData() {}
 
 bool ActivityUserData::CreateSnapshot(Snapshot* output_snapshot) const {
   DCHECK(output_snapshot);
   DCHECK(output_snapshot->empty());
 
   // Find any new data that may have been added by an active instance of this
   // class that is adding records.
   ImportExistingData();
 
+  // Add all the values to the snapshot.
   for (const auto& entry : values_) {
     TypedValue value;
+    const size_t size = entry.second.size_ptr->load(std::memory_order_acquire);
     value.type_ = entry.second.type;
-    DCHECK_GE(entry.second.extent,
-              entry.second.size_ptr->load(std::memory_order_relaxed));
+    DCHECK_GE(entry.second.extent, size);
 
     switch (entry.second.type) {
       case RAW_VALUE:
       case STRING_VALUE:
         value.long_value_ =
-            std::string(reinterpret_cast<char*>(entry.second.memory),
-                        entry.second.size_ptr->load(std::memory_order_relaxed));
+            std::string(reinterpret_cast<char*>(entry.second.memory), size);
         break;
       case RAW_VALUE_REFERENCE:
       case STRING_VALUE_REFERENCE: {
         ReferenceRecord* ref =
             reinterpret_cast<ReferenceRecord*>(entry.second.memory);
         value.ref_value_ = StringPiece(
             reinterpret_cast<char*>(static_cast<uintptr_t>(ref->address)),
             static_cast<size_t>(ref->size));
       } break;
       case BOOL_VALUE:
       case CHAR_VALUE:
         value.short_value_ = *reinterpret_cast<char*>(entry.second.memory);
         break;
       case SIGNED_VALUE:
       case UNSIGNED_VALUE:
         value.short_value_ = *reinterpret_cast<uint64_t*>(entry.second.memory);
         break;
       case END_OF_VALUES:  // Included for completeness purposes.
         NOTREACHED();
     }
     auto inserted = output_snapshot->insert(
         std::make_pair(entry.second.name.as_string(), std::move(value)));
     DCHECK(inserted.second);  // True if inserted, false if existed.
   }
 
+  // Another import attempt will validate that the underlying memory has not
+  // been reused for another purpose. Entries added since the first import
+  // will be ignored here but will be returned if another snapshot is created.
+  ImportExistingData();
+  if (!memory_) {
+    output_snapshot->clear();
+    return false;
+  }
+
+  // Successful snapshot.
   return true;
 }
 
 const void* ActivityUserData::GetBaseAddress() const {
   // The |memory_| pointer advances as elements are written but the |header_|
   // value is always at the start of the block so just return that.
   return header_;
 }
 
 void ActivityUserData::SetOwningProcessIdForTesting(ProcessId pid,
@@ skipping 12 matching lines @@
 }
 
 void ActivityUserData::Set(StringPiece name,
                            ValueType type,
                            const void* memory,
                            size_t size) {
   DCHECK_GE(std::numeric_limits<uint8_t>::max(), name.length());
   size = std::min(std::numeric_limits<uint16_t>::max() - (kMemoryAlignment - 1),
                   size);
 
+  // Find any new data that may have been added by an active instance of this

[manzagop (departed), 2017/03/21 21:10:05]

Can you say more about what/where this other instance is? IIUC there'd need to
be some locking for the writes not to step on each other's toes below?

[bcwhite, 2017/03/29 22:00:51]

You're right.  I was once thinking they could operate independently but that's a
lot more lock-free work than is necessary and would only be needed if "global
data" makes a return.

Note that the CL that removes "global data" depends on this one landing first. 
Oh well.

+  // class that is adding records. This comes before the memory_ test below
+  // because this call can clear the memory_ pointer if it finds a problem.
+  ImportExistingData();
+
   // It's possible that no user data is being stored.
   if (!memory_)
     return;
 
   // The storage of a name is limited so use that limit during lookup.
   if (name.length() > kMaxUserDataNameLength)
     name.set(name.data(), kMaxUserDataNameLength);
 
   ValueInfo* info;
   auto existing = values_.find(name);
@@ skipping 81 matching lines @@
                                     ValueType type,
                                     const void* memory,
                                     size_t size) {
   ReferenceRecord rec;
   rec.address = reinterpret_cast<uintptr_t>(memory);
   rec.size = size;
   Set(name, type, &rec, sizeof(rec));
 }
 
 void ActivityUserData::ImportExistingData() const {
+  // It's possible that no user data is being stored.
+  if (!memory_)
+    return;
+
   while (available_ > sizeof(FieldHeader)) {
     FieldHeader* header = reinterpret_cast<FieldHeader*>(memory_);
     ValueType type =
         static_cast<ValueType>(header->type.load(std::memory_order_acquire));
     if (type == END_OF_VALUES)
       return;
     if (header->record_size > available_)
       return;
 
     size_t value_offset = RoundUpToAlignment(
@@ skipping 11 matching lines @@
     info.memory = memory_ + value_offset;
     info.size_ptr = &header->value_size;
     info.extent = header->record_size - value_offset;
 
     StringPiece key(info.name);
     values_.insert(std::make_pair(key, std::move(info)));
 
     memory_ += header->record_size;
     available_ -= header->record_size;
   }
+
+  // Check if memory has been completely reused.
+  if (header_->owner.data_id.load(std::memory_order_acquire) != orig_data_id ||
+      header_->owner.process_id != orig_process_id ||
+      header_->owner.create_stamp != orig_create_stamp) {
+    memory_ = nullptr;

[manzagop (departed), 2017/03/21 21:10:05]

This behavior should be mentioned in the .h.

[bcwhite, 2017/03/29 22:00:51]

Done.

+    values_.clear();
+  }
 }
 
 // This information is kept for every thread that is tracked. It is filled
 // the very first time the thread is seen. All fields must be of exact sizes
 // so there is no issue moving between 32 and 64-bit builds.
 struct ThreadActivityTracker::Header {
   // Defined in .h for analyzer access. Increment this if structure changes!
   static constexpr uint32_t kPersistentTypeId =
       GlobalActivityTracker::kTypeIdActivityTracker;
 
@@ skipping 310 matching lines @@
   // during the time-sensitive snapshot operation. It is shrunk once the
   // actual size is known.
   output_snapshot->activity_stack.reserve(stack_slots_);
 
   for (int attempt = 0; attempt < kMaxAttempts; ++attempt) {
     // Remember the data IDs to ensure nothing is replaced during the snapshot
     // operation. Use "acquire" so that all the non-atomic fields of the
     // structure are valid (at least at the current moment in time).
     const uint32_t starting_id =
         header_->owner.data_id.load(std::memory_order_acquire);
+    const int64_t starting_create_stamp = header_->owner.create_stamp;
     const int64_t starting_process_id = header_->owner.process_id;
     const int64_t starting_thread_id = header_->thread_ref.as_id;
 
     // Write a non-zero value to |stack_unchanged| so it's possible to detect
     // at the end that nothing has changed since copying the data began. A
     // "cst" operation is required to ensure it occurs before everything else.
     // Using "cst" memory ordering is relatively expensive but this is only
     // done during analysis so doesn't directly affect the worker threads.
     header_->stack_unchanged.store(1, std::memory_order_seq_cst);
 
@@ skipping 13 matching lines @@
       continue;
 
     // Stack copied. Record it's full depth.
     output_snapshot->activity_stack_depth = depth;
 
     // TODO(bcwhite): Snapshot other things here.
 
     // Get the general thread information.
     output_snapshot->thread_name =
         std::string(header_->thread_name, sizeof(header_->thread_name) - 1);
+    output_snapshot->create_stamp = header_->owner.create_stamp;
     output_snapshot->thread_id = header_->thread_ref.as_id;
     output_snapshot->process_id = header_->owner.process_id;
 
     // All characters of the thread-name buffer were copied so as to not break
     // if the trailing NUL were missing. Now limit the length if the actual
     // name is shorter.
     output_snapshot->thread_name.resize(
         strlen(output_snapshot->thread_name.c_str()));
 
     // If the data ID has changed then the tracker has exited and the memory
     // reused by a new one. Try again.
     if (header_->owner.data_id.load(std::memory_order_seq_cst) != starting_id ||
+        output_snapshot->create_stamp != starting_create_stamp ||
         output_snapshot->process_id != starting_process_id ||
         output_snapshot->thread_id != starting_thread_id) {
       continue;
     }
 
     // Only successful if the data is still valid once everything is done since
     // it's possible for the thread to end somewhere in the middle and all its
     // values become garbage.
     if (!IsValid())
       return false;
@@ skipping 706 matching lines @@
     : GlobalActivityTracker::ScopedThreadActivity(
           program_counter,
           nullptr,
           Activity::ACT_PROCESS_WAIT,
           ActivityData::ForProcess(process->Pid()),
           /*lock_allowed=*/true) {}
 #endif
 
 }  // namespace debug
 }  // namespace base