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// Copyright 2018 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/sampling_heap_profiler/poisson_allocation_sampler.h"
#include <algorithm>
#include <atomic>
#include <cmath>
#include <utility>
#include "base/allocator/allocator_shim.h"
#include "base/allocator/buildflags.h"
#include "base/allocator/partition_allocator/partition_alloc.h"
#include "base/macros.h"
#include "base/no_destructor.h"
#include "base/partition_alloc_buildflags.h"
#include "base/rand_util.h"
#include "base/sampling_heap_profiler/lock_free_address_hash_set.h"
#include "build/build_config.h"
#if defined(OS_MACOSX) || defined(OS_ANDROID)
#include <pthread.h>
#endif
namespace base {
using allocator::AllocatorDispatch;
namespace {
#if defined(OS_MACOSX) || defined(OS_ANDROID)
// The macOS implementation of libmalloc sometimes calls malloc recursively,
// delegating allocations between zones. That causes our hooks being called
// twice. The scoped guard allows us to detect that.
//
// Besides that the implementations of thread_local on macOS and Android
// seem to allocate memory lazily on the first access to thread_local variables.
// Make use of pthread TLS instead of C++ thread_local there.
class ReentryGuard {
public:
ReentryGuard() : allowed_(!pthread_getspecific(entered_key_)) {
pthread_setspecific(entered_key_, reinterpret_cast<void*>(true));
}
~ReentryGuard() {
if (LIKELY(allowed_))
pthread_setspecific(entered_key_, nullptr);
}
operator bool() { return allowed_; }
static void Init() {
int error = pthread_key_create(&entered_key_, nullptr);
CHECK(!error);
}
private:
bool allowed_;
static pthread_key_t entered_key_;
};
pthread_key_t ReentryGuard::entered_key_;
#else
class ReentryGuard {
public:
operator bool() { return true; }
static void Init() {}
};
#endif
const size_t kDefaultSamplingIntervalBytes = 128 * 1024;
// Notes on TLS usage:
//
// * There's no safe way to use TLS in malloc() as both C++ thread_local and
// pthread do not pose any guarantees on whether they allocate or not.
// * We think that we can safely use thread_local w/o re-entrancy guard because
// the compiler will use "tls static access model" for static builds of
// Chrome [https://www.uclibc.org/docs/tls.pdf].
// But there's no guarantee that this will stay true, and in practice
// it seems to have problems on macOS/Android. These platforms do allocate
// on the very first access to a thread_local on each thread.
// * Directly using/warming-up platform TLS seems to work on all platforms,
// but is also not guaranteed to stay true. We make use of it for reentrancy
// guards on macOS/Android.
// * We cannot use Windows Tls[GS]etValue API as it modifies the result of
// GetLastError.
//
// Android thread_local seems to be using __emutls_get_address from libgcc:
// https://github.com/gcc-mirror/gcc/blob/master/libgcc/emutls.c
// macOS version is based on _tlv_get_addr from dyld:
// https://opensource.apple.com/source/dyld/dyld-635.2/src/threadLocalHelpers.s.auto.html
// The guard protects against reentering on platforms other the macOS and
// Android.
thread_local bool g_internal_reentry_guard;
// Accumulated bytes towards sample thread local key.
thread_local intptr_t g_accumulated_bytes_tls;
// A boolean used to distinguish first allocation on a thread:
// false - first allocation on the thread;
// true - otherwise.
// Since g_accumulated_bytes_tls is initialized with zero the very first
// allocation on a thread would always trigger the sample, thus skewing the
// profile towards such allocations. To mitigate that we use the flag to
// ensure the first allocation is properly accounted.
thread_local bool g_sampling_interval_initialized_tls;
// Controls if sample intervals should not be randomized. Used for testing.
bool g_deterministic;
// A positive value if profiling is running, otherwise it's zero.
std::atomic_bool g_running;
// Pointer to the current |LockFreeAddressHashSet|.
std::atomic<LockFreeAddressHashSet*> g_sampled_addresses_set;
// Sampling interval parameter, the mean value for intervals between samples.
std::atomic_size_t g_sampling_interval{kDefaultSamplingIntervalBytes};
void (*g_hooks_install_callback)();
std::atomic_bool g_hooks_installed;
void* AllocFn(const AllocatorDispatch* self, size_t size, void* context) {
ReentryGuard guard;
void* address = self->next->alloc_function(self->next, size, context);
if (LIKELY(guard)) {
PoissonAllocationSampler::RecordAlloc(
address, size, PoissonAllocationSampler::kMalloc, nullptr);
}
return address;
}
void* AllocZeroInitializedFn(const AllocatorDispatch* self,
size_t n,
size_t size,
void* context) {
ReentryGuard guard;
void* address =
self->next->alloc_zero_initialized_function(self->next, n, size, context);
if (LIKELY(guard)) {
PoissonAllocationSampler::RecordAlloc(
address, n * size, PoissonAllocationSampler::kMalloc, nullptr);
}
return address;
}
void* AllocAlignedFn(const AllocatorDispatch* self,
size_t alignment,
size_t size,
void* context) {
ReentryGuard guard;
void* address =
self->next->alloc_aligned_function(self->next, alignment, size, context);
if (LIKELY(guard)) {
PoissonAllocationSampler::RecordAlloc(
address, size, PoissonAllocationSampler::kMalloc, nullptr);
}
return address;
}
void* ReallocFn(const AllocatorDispatch* self,
void* address,
size_t size,
void* context) {
ReentryGuard guard;
// Note: size == 0 actually performs free.
PoissonAllocationSampler::RecordFree(address);
address = self->next->realloc_function(self->next, address, size, context);
if (LIKELY(guard)) {
PoissonAllocationSampler::RecordAlloc(
address, size, PoissonAllocationSampler::kMalloc, nullptr);
}
return address;
}
void FreeFn(const AllocatorDispatch* self, void* address, void* context) {
// Note: The RecordFree should be called before free_function
// (here and in other places).
// That is because we need to remove the recorded allocation sample before
// free_function, as once the latter is executed the address becomes available
// and can be allocated by another thread. That would be racy otherwise.
PoissonAllocationSampler::RecordFree(address);
self->next->free_function(self->next, address, context);
}
size_t GetSizeEstimateFn(const AllocatorDispatch* self,
void* address,
void* context) {
return self->next->get_size_estimate_function(self->next, address, context);
}
unsigned BatchMallocFn(const AllocatorDispatch* self,
size_t size,
void** results,
unsigned num_requested,
void* context) {
ReentryGuard guard;
unsigned num_allocated = self->next->batch_malloc_function(
self->next, size, results, num_requested, context);
if (LIKELY(guard)) {
for (unsigned i = 0; i < num_allocated; ++i) {
PoissonAllocationSampler::RecordAlloc(
results[i], size, PoissonAllocationSampler::kMalloc, nullptr);
}
}
return num_allocated;
}
void BatchFreeFn(const AllocatorDispatch* self,
void** to_be_freed,
unsigned num_to_be_freed,
void* context) {
for (unsigned i = 0; i < num_to_be_freed; ++i)
PoissonAllocationSampler::RecordFree(to_be_freed[i]);
self->next->batch_free_function(self->next, to_be_freed, num_to_be_freed,
context);
}
void FreeDefiniteSizeFn(const AllocatorDispatch* self,
void* address,
size_t size,
void* context) {
PoissonAllocationSampler::RecordFree(address);
self->next->free_definite_size_function(self->next, address, size, context);
}
static void* AlignedMallocFn(const AllocatorDispatch* self,
size_t size,
size_t alignment,
void* context) {
ReentryGuard guard;
void* address =
self->next->aligned_malloc_function(self->next, size, alignment, context);
if (LIKELY(guard)) {
PoissonAllocationSampler::RecordAlloc(
address, size, PoissonAllocationSampler::kMalloc, nullptr);
}
return address;
}
static void* AlignedReallocFn(const AllocatorDispatch* self,
void* address,
size_t size,
size_t alignment,
void* context) {
ReentryGuard guard;
// Note: size == 0 actually performs free.
PoissonAllocationSampler::RecordFree(address);
address = self->next->aligned_realloc_function(self->next, address, size,
alignment, context);
if (LIKELY(guard)) {
PoissonAllocationSampler::RecordAlloc(
address, size, PoissonAllocationSampler::kMalloc, nullptr);
}
return address;
}
static void AlignedFreeFn(const AllocatorDispatch* self,
void* address,
void* context) {
PoissonAllocationSampler::RecordFree(address);
self->next->aligned_free_function(self->next, address, context);
}
AllocatorDispatch g_allocator_dispatch = {&AllocFn,
&AllocZeroInitializedFn,
&AllocAlignedFn,
&ReallocFn,
&FreeFn,
&GetSizeEstimateFn,
&BatchMallocFn,
&BatchFreeFn,
&FreeDefiniteSizeFn,
&AlignedMallocFn,
&AlignedReallocFn,
&AlignedFreeFn,
nullptr};
#if BUILDFLAG(USE_PARTITION_ALLOC) && !defined(OS_NACL)
void PartitionAllocHook(void* address, size_t size, const char* type) {
PoissonAllocationSampler::RecordAlloc(
address, size, PoissonAllocationSampler::kPartitionAlloc, type);
}
void PartitionFreeHook(void* address) {
PoissonAllocationSampler::RecordFree(address);
}
#endif // BUILDFLAG(USE_PARTITION_ALLOC) && !defined(OS_NACL)
} // namespace
PoissonAllocationSampler::ScopedMuteThreadSamples::ScopedMuteThreadSamples() {
DCHECK(!g_internal_reentry_guard);
g_internal_reentry_guard = true;
}
PoissonAllocationSampler::ScopedMuteThreadSamples::~ScopedMuteThreadSamples() {
DCHECK(g_internal_reentry_guard);
g_internal_reentry_guard = false;
}
// static
bool PoissonAllocationSampler::ScopedMuteThreadSamples::IsMuted() {
return g_internal_reentry_guard;
}
PoissonAllocationSampler* PoissonAllocationSampler::instance_;
PoissonAllocationSampler::PoissonAllocationSampler() {
CHECK_EQ(nullptr, instance_);
instance_ = this;
Init();
auto sampled_addresses = std::make_unique<LockFreeAddressHashSet>(64);
g_sampled_addresses_set = sampled_addresses.get();
sampled_addresses_stack_.push_back(std::move(sampled_addresses));
}
// static
void PoissonAllocationSampler::Init() {
static bool init_once = []() {
ReentryGuard::Init();
return true;
}();
ignore_result(init_once);
}
// static
void PoissonAllocationSampler::InstallAllocatorHooksOnce() {
static bool hook_installed = InstallAllocatorHooks();
ignore_result(hook_installed);
}
// static
bool PoissonAllocationSampler::InstallAllocatorHooks() {
#if BUILDFLAG(USE_ALLOCATOR_SHIM)
allocator::InsertAllocatorDispatch(&g_allocator_dispatch);
#else
ignore_result(g_allocator_dispatch);
DLOG(WARNING)
<< "base::allocator shims are not available for memory sampling.";
#endif // BUILDFLAG(USE_ALLOCATOR_SHIM)
#if BUILDFLAG(USE_PARTITION_ALLOC) && !defined(OS_NACL)
PartitionAllocHooks::SetAllocationHook(&PartitionAllocHook);
PartitionAllocHooks::SetFreeHook(&PartitionFreeHook);
#endif // BUILDFLAG(USE_PARTITION_ALLOC) && !defined(OS_NACL)
bool expected = false;
if (!g_hooks_installed.compare_exchange_strong(expected, true))
g_hooks_install_callback();
return true;
}
// static
void PoissonAllocationSampler::SetHooksInstallCallback(
void (*hooks_install_callback)()) {
CHECK(!g_hooks_install_callback && hooks_install_callback);
g_hooks_install_callback = hooks_install_callback;
bool expected = false;
if (!g_hooks_installed.compare_exchange_strong(expected, true))
g_hooks_install_callback();
}
void PoissonAllocationSampler::SetSamplingInterval(size_t sampling_interval) {
// TODO(alph): Reset the sample being collected if running.
g_sampling_interval = sampling_interval;
}
// static
size_t PoissonAllocationSampler::GetNextSampleInterval(size_t interval) {
if (UNLIKELY(g_deterministic))
return interval;
// We sample with a Poisson process, with constant average sampling
// interval. This follows the exponential probability distribution with
// parameter λ = 1/interval where |interval| is the average number of bytes
// between samples.
// Let u be a uniformly distributed random number between 0 and 1, then
// next_sample = -ln(u) / λ
double uniform = RandDouble();
double value = -log(uniform) * interval;
size_t min_value = sizeof(intptr_t);
// We limit the upper bound of a sample interval to make sure we don't have
// huge gaps in the sampling stream. Probability of the upper bound gets hit
// is exp(-20) ~ 2e-9, so it should not skew the distribution.
size_t max_value = interval * 20;
if (UNLIKELY(value < min_value))
return min_value;
if (UNLIKELY(value > max_value))
return max_value;
return static_cast<size_t>(value);
}
// static
void PoissonAllocationSampler::RecordAlloc(void* address,
size_t size,
AllocatorType type,
const char* context) {
if (UNLIKELY(!g_running.load(std::memory_order_relaxed)))
return;
g_accumulated_bytes_tls += size;
intptr_t accumulated_bytes = g_accumulated_bytes_tls;
if (LIKELY(accumulated_bytes < 0))
return;
instance_->DoRecordAlloc(accumulated_bytes, size, address, type, context);
}
void PoissonAllocationSampler::DoRecordAlloc(intptr_t accumulated_bytes,
size_t size,
void* address,
AllocatorType type,
const char* context) {
// Failed allocation? Skip the sample.
if (UNLIKELY(!address))
return;
size_t mean_interval = g_sampling_interval.load(std::memory_order_relaxed);
size_t samples = accumulated_bytes / mean_interval;
accumulated_bytes %= mean_interval;
do {
accumulated_bytes -= GetNextSampleInterval(mean_interval);
++samples;
} while (accumulated_bytes >= 0);
g_accumulated_bytes_tls = accumulated_bytes;
if (UNLIKELY(!g_sampling_interval_initialized_tls)) {
g_sampling_interval_initialized_tls = true;
// This is the very first allocation on the thread. It always produces an
// extra sample because g_accumulated_bytes_tls is initialized with zero
// due to TLS semantics.
// Make sure we don't count this extra sample.
if (!--samples)
return;
}
if (UNLIKELY(ScopedMuteThreadSamples::IsMuted()))
return;
ScopedMuteThreadSamples no_reentrancy_scope;
AutoLock lock(mutex_);
// TODO(alph): Sometimes RecordAlloc is called twice in a row without
// a RecordFree in between. Investigate it.
if (sampled_addresses_set().Contains(address))
return;
sampled_addresses_set().Insert(address);
BalanceAddressesHashSet();
size_t total_allocated = mean_interval * samples;
for (auto* observer : observers_)
observer->SampleAdded(address, size, total_allocated, type, context);
}
// static
void PoissonAllocationSampler::RecordFree(void* address) {
if (UNLIKELY(address == nullptr))
return;
if (UNLIKELY(sampled_addresses_set().Contains(address)))
instance_->DoRecordFree(address);
}
void PoissonAllocationSampler::DoRecordFree(void* address) {
if (UNLIKELY(ScopedMuteThreadSamples::IsMuted()))
return;
// There is a rare case on macOS and Android when the very first thread_local
// access in ScopedMuteThreadSamples constructor may allocate and
// thus reenter DoRecordAlloc. However the call chain won't build up further
// as RecordAlloc accesses are guarded with pthread TLS-based ReentryGuard.
ScopedMuteThreadSamples no_reentrancy_scope;
AutoLock lock(mutex_);
for (auto* observer : observers_)
observer->SampleRemoved(address);
sampled_addresses_set().Remove(address);
}
void PoissonAllocationSampler::BalanceAddressesHashSet() {
// Check if the load_factor of the current addresses hash set becomes higher
// than 1, allocate a new twice larger one, copy all the data,
// and switch to using it.
// During the copy process no other writes are made to both sets
// as it's behind the lock.
// All the readers continue to use the old one until the atomic switch
// process takes place.
LockFreeAddressHashSet& current_set = sampled_addresses_set();
if (current_set.load_factor() < 1)
return;
auto new_set =
std::make_unique<LockFreeAddressHashSet>(current_set.buckets_count() * 2);
new_set->Copy(current_set);
// Atomically switch all the new readers to the new set.
g_sampled_addresses_set = new_set.get();
// We still have to keep all the old maps alive to resolve the theoretical
// race with readers in |RecordFree| that have already obtained the map,
// but haven't yet managed to access it.
sampled_addresses_stack_.push_back(std::move(new_set));
}
// static
LockFreeAddressHashSet& PoissonAllocationSampler::sampled_addresses_set() {
return *g_sampled_addresses_set.load(std::memory_order_relaxed);
}
// static
PoissonAllocationSampler* PoissonAllocationSampler::Get() {
static NoDestructor<PoissonAllocationSampler> instance;
return instance.get();
}
// static
void PoissonAllocationSampler::SuppressRandomnessForTest(bool suppress) {
g_deterministic = suppress;
}
void PoissonAllocationSampler::AddSamplesObserver(SamplesObserver* observer) {
ScopedMuteThreadSamples no_reentrancy_scope;
AutoLock lock(mutex_);
observers_.push_back(observer);
InstallAllocatorHooksOnce();
g_running = !observers_.empty();
}
void PoissonAllocationSampler::RemoveSamplesObserver(
SamplesObserver* observer) {
ScopedMuteThreadSamples no_reentrancy_scope;
AutoLock lock(mutex_);
auto it = std::find(observers_.begin(), observers_.end(), observer);
CHECK(it != observers_.end());
observers_.erase(it);
g_running = !observers_.empty();
}
} // namespace base