base/trace_event/heap_profiler_allocation_context_tracker.cc

// Copyright 2015 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/trace_event/heap_profiler_allocation_context_tracker.h"

#include <algorithm>
#include <iterator>

#include "base/atomicops.h"
#include "base/debug/leak_annotations.h"
#include "base/threading/platform_thread.h"
#include "base/threading/thread_local_storage.h"
#include "base/trace_event/heap_profiler_allocation_context.h"

#if defined(OS_LINUX) || defined(OS_ANDROID)
#include <sys/prctl.h>
#endif

namespace base {
namespace trace_event {

subtle::Atomic32 AllocationContextTracker::capture_mode_ =
    static_cast<int32_t>(AllocationContextTracker::CaptureMode::DISABLED);

namespace {

const size_t kMaxStackDepth = 128u;
const size_t kMaxTaskDepth = 16u;
AllocationContextTracker* const kInitializingSentinel =
    reinterpret_cast<AllocationContextTracker*>(-1);
const char kTracingOverhead[] = "tracing_overhead";

ThreadLocalStorage::StaticSlot g_tls_alloc_ctx_tracker = TLS_INITIALIZER;

// This function is added to the TLS slot to clean up the instance when the
// thread exits.
void DestructAllocationContextTracker(void* alloc_ctx_tracker) {
  delete static_cast<AllocationContextTracker*>(alloc_ctx_tracker);
}

// Cannot call ThreadIdNameManager::GetName because it holds a lock and causes
// deadlock when lock is already held by ThreadIdNameManager before the current
// allocation. Gets the thread name from kernel if available or returns a string
// with id. This function intenionally leaks the allocated strings since they
// are used to tag allocations even after the thread dies.
const char* GetAndLeakThreadName() {
  char name[16];
#if defined(OS_LINUX) || defined(OS_ANDROID)
  // If the thread name is not set, try to get it from prctl. Thread name might
  // not be set in cases where the thread started before heap profiling was
  // enabled.
  int err = prctl(PR_GET_NAME, name);
  if (!err) {
    return strdup(name);
  }
#endif  // defined(OS_LINUX) || defined(OS_ANDROID)

  // Use tid if we don't have a thread name.
  snprintf(name, sizeof(name), "%lu",
           static_cast<unsigned long>(PlatformThread::CurrentId()));
  return strdup(name);
}

}  // namespace

// static
AllocationContextTracker*
AllocationContextTracker::GetInstanceForCurrentThread() {
  AllocationContextTracker* tracker =
      static_cast<AllocationContextTracker*>(g_tls_alloc_ctx_tracker.Get());
  if (tracker == kInitializingSentinel)
    return nullptr;  // Re-entrancy case.

  if (!tracker) {
    g_tls_alloc_ctx_tracker.Set(kInitializingSentinel);
    tracker = new AllocationContextTracker();
    g_tls_alloc_ctx_tracker.Set(tracker);
  }

  return tracker;
}

AllocationContextTracker::AllocationContextTracker()
    : thread_name_(nullptr), ignore_scope_depth_(0) {
  pseudo_stack_.reserve(kMaxStackDepth);
  task_contexts_.reserve(kMaxTaskDepth);
}
AllocationContextTracker::~AllocationContextTracker() {}

// static
void AllocationContextTracker::SetCurrentThreadName(const char* name) {
  if (name && capture_mode() != CaptureMode::DISABLED) {
    GetInstanceForCurrentThread()->thread_name_ = name;
  }
}

// static
void AllocationContextTracker::SetCaptureMode(CaptureMode mode) {
  // When enabling capturing, also initialize the TLS slot. This does not create
  // a TLS instance yet.
  if (mode != CaptureMode::DISABLED && !g_tls_alloc_ctx_tracker.initialized())
    g_tls_alloc_ctx_tracker.Initialize(DestructAllocationContextTracker);

  // Release ordering ensures that when a thread observes |capture_mode_| to
  // be true through an acquire load, the TLS slot has been initialized.
  subtle::Release_Store(&capture_mode_, static_cast<int32_t>(mode));
}

void AllocationContextTracker::PushPseudoStackFrame(
    const char* trace_event_name) {
  // Impose a limit on the height to verify that every push is popped, because
  // in practice the pseudo stack never grows higher than ~20 frames.
  if (pseudo_stack_.size() < kMaxStackDepth)
    pseudo_stack_.push_back(trace_event_name);
  else
    NOTREACHED();
}

void AllocationContextTracker::PopPseudoStackFrame(
    const char* trace_event_name) {
  // Guard for stack underflow. If tracing was started with a TRACE_EVENT in
  // scope, the frame was never pushed, so it is possible that pop is called
  // on an empty stack.
  if (pseudo_stack_.empty())
    return;

  // Assert that pushes and pops are nested correctly. This DCHECK can be
  // hit if some TRACE_EVENT macro is unbalanced (a TRACE_EVENT_END* call
  // without a corresponding TRACE_EVENT_BEGIN).
  DCHECK_EQ(trace_event_name, pseudo_stack_.back())
      << "Encountered an unmatched TRACE_EVENT_END";

  pseudo_stack_.pop_back();
}

void AllocationContextTracker::PushCurrentTaskContext(const char* context) {
  DCHECK(context);
  if (task_contexts_.size() < kMaxTaskDepth)
    task_contexts_.push_back(context);
  else
    NOTREACHED();
}

void AllocationContextTracker::PopCurrentTaskContext(const char* context) {
  // Guard for stack underflow. If tracing was started with a TRACE_EVENT in
  // scope, the context was never pushed, so it is possible that pop is called
  // on an empty stack.
  if (task_contexts_.empty())
    return;

  DCHECK_EQ(context, task_contexts_.back())
      << "Encountered an unmatched context end";
  task_contexts_.pop_back();
}

// static
AllocationContext AllocationContextTracker::GetContextSnapshot() {
  AllocationContext ctx;

  if (ignore_scope_depth_) {
    ctx.backtrace.frames[0] = StackFrame::FromTraceEventName(kTracingOverhead);
    ctx.type_name = kTracingOverhead;
    ctx.backtrace.frame_count = 1;
    return ctx;
  }

  CaptureMode mode = static_cast<CaptureMode>(
      subtle::NoBarrier_Load(&capture_mode_));

  auto backtrace = std::begin(ctx.backtrace.frames);
  auto backtrace_end = std::end(ctx.backtrace.frames);

  if (!thread_name_) {
    // Ignore the string allocation made by GetAndLeakThreadName to avoid
    // reentrancy.
    ignore_scope_depth_++;
    thread_name_ = GetAndLeakThreadName();
    ANNOTATE_LEAKING_OBJECT_PTR(thread_name_);
    DCHECK(thread_name_);
    ignore_scope_depth_--;
  }

  // Add the thread name as the first entry in pseudo stack.
  if (thread_name_) {
    *backtrace++ = StackFrame::FromThreadName(thread_name_);
  }

  switch (mode) {
    case CaptureMode::DISABLED:
      {
        break;
      }
    case CaptureMode::PSEUDO_STACK:
      {
        for (const char* event_name: pseudo_stack_) {
          if (backtrace == backtrace_end) {
            break;
          }
          *backtrace++ = StackFrame::FromTraceEventName(event_name);
        }
        break;
      }
    case CaptureMode::NATIVE_STACK:
      {
        // Backtrace contract requires us to return bottom frames, i.e.
        // from main() and up. Stack unwinding produces top frames, i.e.
        // from this point and up until main(). We request many frames to
        // make sure we reach main(), and then copy bottom portion of them.
        const void* frames[128];
        static_assert(arraysize(frames) >= Backtrace::kMaxFrameCount,
                      "not requesting enough frames to fill Backtrace");
#if HAVE_TRACE_STACK_FRAME_POINTERS && !defined(OS_NACL)
        size_t frame_count = debug::TraceStackFramePointers(
            frames,
            arraysize(frames),
            1 /* exclude this function from the trace */ );
#else
        size_t frame_count = 0;
        NOTREACHED();
#endif

        // Copy frames backwards
        size_t backtrace_capacity = backtrace_end - backtrace;
        size_t top_frame_index = (backtrace_capacity >= frame_count) ?
            0 :
            frame_count - backtrace_capacity;
        for (size_t i = frame_count; i > top_frame_index;) {
          const void* frame = frames[--i];
          *backtrace++ = StackFrame::FromProgramCounter(frame);
        }
        break;
      }
  }

  ctx.backtrace.frame_count = backtrace - std::begin(ctx.backtrace.frames);

  // TODO(ssid): Fix crbug.com/594803 to add file name as 3rd dimension
  // (component name) in the heap profiler and not piggy back on the type name.
  ctx.type_name = task_contexts_.empty() ? nullptr : task_contexts_.back();

  return ctx;
}

}  // namespace trace_event
}  // namespace base