root/third_party/tcmalloc/chromium/src/thread_cache.cc

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DEFINITIONS

This source file includes following definitions.
  1. CheckIfKernelSupportsTLS
  2. CheckIfKernelSupportsTLS
  3. CheckIfKernelSupportsTLS
  4. Init
  5. Cleanup
  6. FetchFromCentralCache
  7. ListTooLong
  8. ReleaseToCentralCache
  9. Scavenge
  10. IncreaseCacheLimit
  11. IncreaseCacheLimitLocked
  12. GetSamplePeriod
  13. GetBytesAllocatedOnCurrentThread
  14. InitModule
  15. InitTSD
  16. CreateCacheIfNecessary
  17. NewHeap
  18. BecomeIdle
  19. DestroyThreadCache
  20. DeleteCache
  21. RecomputePerThreadCacheSize
  22. GetThreadStats
  23. set_overall_thread_cache_size

// Copyright (c) 2008, Google Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

// ---
// Author: Ken Ashcraft <opensource@google.com>

#include <config.h>
#include "thread_cache.h"
#include <errno.h>
#include <string.h>                     // for memcpy
#include <algorithm>                    // for max, min
#include "base/commandlineflags.h"      // for SpinLockHolder
#include "base/spinlock.h"              // for SpinLockHolder
#include "central_freelist.h"           // for CentralFreeListPadded
#include "maybe_threads.h"

using std::min;
using std::max;

DEFINE_int64(tcmalloc_max_total_thread_cache_bytes,
             EnvToInt64("TCMALLOC_MAX_TOTAL_THREAD_CACHE_BYTES",
                        kDefaultOverallThreadCacheSize),
             "Bound on the total amount of bytes allocated to "
             "thread caches. This bound is not strict, so it is possible "
             "for the cache to go over this bound in certain circumstances. "
             "Maximum value of this flag is capped to 1 GB.");

namespace tcmalloc {

static bool phinited = false;

volatile size_t ThreadCache::per_thread_cache_size_ = kMaxThreadCacheSize;
size_t ThreadCache::overall_thread_cache_size_ = kDefaultOverallThreadCacheSize;
ssize_t ThreadCache::unclaimed_cache_space_ = kDefaultOverallThreadCacheSize;
PageHeapAllocator<ThreadCache> threadcache_allocator;
ThreadCache* ThreadCache::thread_heaps_ = NULL;
int ThreadCache::thread_heap_count_ = 0;
ThreadCache* ThreadCache::next_memory_steal_ = NULL;
#ifdef HAVE_TLS
__thread ThreadCache* ThreadCache::threadlocal_heap_
// See comments in thread_cache.h about this. Bug here:
// http://code.google.com/p/chromium/issues/detail?id=124489
#if defined(HAVE___ATTRIBUTE__) && !defined(PGO_GENERATE)
   __attribute__ ((tls_model ("initial-exec")))
# endif
   ;
#endif
bool ThreadCache::tsd_inited_ = false;
pthread_key_t ThreadCache::heap_key_;

#if defined(HAVE_TLS)
bool kernel_supports_tls = false;      // be conservative
# if defined(_WIN32)    // windows has supported TLS since winnt, I think.
    void CheckIfKernelSupportsTLS() {
      kernel_supports_tls = true;
    }
# elif !HAVE_DECL_UNAME    // if too old for uname, probably too old for TLS
    void CheckIfKernelSupportsTLS() {
      kernel_supports_tls = false;
    }
# else
#   include <sys/utsname.h>    // DECL_UNAME checked for <sys/utsname.h> too
    void CheckIfKernelSupportsTLS() {
      struct utsname buf;
      if (uname(&buf) < 0) {   // should be impossible
        Log(kLog, __FILE__, __LINE__,
            "uname failed assuming no TLS support (errno)", errno);
        kernel_supports_tls = false;
      } else if (strcasecmp(buf.sysname, "linux") == 0) {
        // The linux case: the first kernel to support TLS was 2.6.0
        if (buf.release[0] < '2' && buf.release[1] == '.')    // 0.x or 1.x
          kernel_supports_tls = false;
        else if (buf.release[0] == '2' && buf.release[1] == '.' &&
                 buf.release[2] >= '0' && buf.release[2] < '6' &&
                 buf.release[3] == '.')                       // 2.0 - 2.5
          kernel_supports_tls = false;
        else
          kernel_supports_tls = true;
      } else if (strcasecmp(buf.sysname, "CYGWIN_NT-6.1-WOW64") == 0) {
        // In my testing, this version of cygwin, at least, would hang
        // when using TLS.
        kernel_supports_tls = false;
      } else {        // some other kernel, we'll be optimisitic
        kernel_supports_tls = true;
      }
      // TODO(csilvers): VLOG(1) the tls status once we support RAW_VLOG
    }
#  endif  // HAVE_DECL_UNAME
#endif    // HAVE_TLS

void ThreadCache::Init(pthread_t tid) {
  size_ = 0;
  total_bytes_allocated_ = 0;

  max_size_ = 0;
  IncreaseCacheLimitLocked();
  if (max_size_ == 0) {
    // There isn't enough memory to go around.  Just give the minimum to
    // this thread.
    max_size_ = kMinThreadCacheSize;

    // Take unclaimed_cache_space_ negative.
    unclaimed_cache_space_ -= kMinThreadCacheSize;
    ASSERT(unclaimed_cache_space_ < 0);
  }

  next_ = NULL;
  prev_ = NULL;
  tid_  = tid;
  in_setspecific_ = false;
  for (size_t cl = 0; cl < kNumClasses; ++cl) {
    list_[cl].Init();
  }

  uint32_t sampler_seed;
  memcpy(&sampler_seed, &tid, sizeof(sampler_seed));
  sampler_.Init(sampler_seed);
}

void ThreadCache::Cleanup() {
  // Put unused memory back into central cache
  for (int cl = 0; cl < kNumClasses; ++cl) {
    if (list_[cl].length() > 0) {
      ReleaseToCentralCache(&list_[cl], cl, list_[cl].length());
    }
  }
}

// Remove some objects of class "cl" from central cache and add to thread heap.
// On success, return the first object for immediate use; otherwise return NULL.
void* ThreadCache::FetchFromCentralCache(size_t cl, size_t byte_size) {
  FreeList* list = &list_[cl];
  ASSERT(list->empty());
  const int batch_size = Static::sizemap()->num_objects_to_move(cl);

  const int num_to_move = min<int>(list->max_length(), batch_size);
  void *start, *end;
  int fetch_count = Static::central_cache()[cl].RemoveRange(
      &start, &end, num_to_move);

  ASSERT((start == NULL) == (fetch_count == 0));
  if (--fetch_count >= 0) {
    size_ += byte_size * fetch_count;
    // Pop the top of the list and add the rest to the freelist.
    void *second = start;
    start = FL_Pop(&second);
    list->PushRange(fetch_count, second, end);
  }

  // Increase max length slowly up to batch_size.  After that,
  // increase by batch_size in one shot so that the length is a
  // multiple of batch_size.
  if (list->max_length() < batch_size) {
    list->set_max_length(list->max_length() + 1);
  } else {
    // Don't let the list get too long.  In 32 bit builds, the length
    // is represented by a 16 bit int, so we need to watch out for
    // integer overflow.
    int new_length = min<int>(list->max_length() + batch_size,
                              kMaxDynamicFreeListLength);
    // The list's max_length must always be a multiple of batch_size,
    // and kMaxDynamicFreeListLength is not necessarily a multiple
    // of batch_size.
    new_length -= new_length % batch_size;
    ASSERT(new_length % batch_size == 0);
    list->set_max_length(new_length);
  }
  return start;
}

void ThreadCache::ListTooLong(FreeList* list, size_t cl) {
  const int batch_size = Static::sizemap()->num_objects_to_move(cl);
  ReleaseToCentralCache(list, cl, batch_size);

  // If the list is too long, we need to transfer some number of
  // objects to the central cache.  Ideally, we would transfer
  // num_objects_to_move, so the code below tries to make max_length
  // converge on num_objects_to_move.

  if (list->max_length() < batch_size) {
    // Slow start the max_length so we don't overreserve.
    list->set_max_length(list->max_length() + 1);
  } else if (list->max_length() > batch_size) {
    // If we consistently go over max_length, shrink max_length.  If we don't
    // shrink it, some amount of memory will always stay in this freelist.
    list->set_length_overages(list->length_overages() + 1);
    if (list->length_overages() > kMaxOverages) {
      ASSERT(list->max_length() > batch_size);
      list->set_max_length(list->max_length() - batch_size);
      list->set_length_overages(0);
    }
  }
}

// Remove some objects of class "cl" from thread heap and add to central cache
void ThreadCache::ReleaseToCentralCache(FreeList* src, size_t cl, int N) {
  ASSERT(src == &list_[cl]);
  if (N > src->length()) N = src->length();
  size_t delta_bytes = N * Static::sizemap()->ByteSizeForClass(cl);

  // We return prepackaged chains of the correct size to the central cache.
  // TODO: Use the same format internally in the thread caches?
  int batch_size = Static::sizemap()->num_objects_to_move(cl);
  while (N > batch_size) {
    void *tail, *head;
    src->PopRange(batch_size, &head, &tail);
    Static::central_cache()[cl].InsertRange(head, tail, batch_size);
    N -= batch_size;
  }
  void *tail, *head;
  src->PopRange(N, &head, &tail);
  Static::central_cache()[cl].InsertRange(head, tail, N);
  size_ -= delta_bytes;
}

// Release idle memory to the central cache
void ThreadCache::Scavenge() {
  // If the low-water mark for the free list is L, it means we would
  // not have had to allocate anything from the central cache even if
  // we had reduced the free list size by L.  We aim to get closer to
  // that situation by dropping L/2 nodes from the free list.  This
  // may not release much memory, but if so we will call scavenge again
  // pretty soon and the low-water marks will be high on that call.
  //int64 start = CycleClock::Now();
  for (int cl = 0; cl < kNumClasses; cl++) {
    FreeList* list = &list_[cl];
    const int lowmark = list->lowwatermark();
    if (lowmark > 0) {
      const int drop = (lowmark > 1) ? lowmark/2 : 1;
      ReleaseToCentralCache(list, cl, drop);

      // Shrink the max length if it isn't used.  Only shrink down to
      // batch_size -- if the thread was active enough to get the max_length
      // above batch_size, it will likely be that active again.  If
      // max_length shinks below batch_size, the thread will have to
      // go through the slow-start behavior again.  The slow-start is useful
      // mainly for threads that stay relatively idle for their entire
      // lifetime.
      const int batch_size = Static::sizemap()->num_objects_to_move(cl);
      if (list->max_length() > batch_size) {
        list->set_max_length(
            max<int>(list->max_length() - batch_size, batch_size));
      }
    }
    list->clear_lowwatermark();
  }

  IncreaseCacheLimit();
}

void ThreadCache::IncreaseCacheLimit() {
  SpinLockHolder h(Static::pageheap_lock());
  IncreaseCacheLimitLocked();
}

void ThreadCache::IncreaseCacheLimitLocked() {
  if (unclaimed_cache_space_ > 0) {
    // Possibly make unclaimed_cache_space_ negative.
    unclaimed_cache_space_ -= kStealAmount;
    max_size_ += kStealAmount;
    return;
  }
  // Don't hold pageheap_lock too long.  Try to steal from 10 other
  // threads before giving up.  The i < 10 condition also prevents an
  // infinite loop in case none of the existing thread heaps are
  // suitable places to steal from.
  for (int i = 0; i < 10;
       ++i, next_memory_steal_ = next_memory_steal_->next_) {
    // Reached the end of the linked list.  Start at the beginning.
    if (next_memory_steal_ == NULL) {
      ASSERT(thread_heaps_ != NULL);
      next_memory_steal_ = thread_heaps_;
    }
    if (next_memory_steal_ == this ||
        next_memory_steal_->max_size_ <= kMinThreadCacheSize) {
      continue;
    }
    next_memory_steal_->max_size_ -= kStealAmount;
    max_size_ += kStealAmount;

    next_memory_steal_ = next_memory_steal_->next_;
    return;
  }
}

int ThreadCache::GetSamplePeriod() {
  return sampler_.GetSamplePeriod();
}

// static
unsigned int ThreadCache::GetBytesAllocatedOnCurrentThread() {
  return ThreadCache::GetThreadHeap()->GetTotalBytesAllocated();
}

void ThreadCache::InitModule() {
  SpinLockHolder h(Static::pageheap_lock());
  if (!phinited) {
    Static::InitStaticVars();
    threadcache_allocator.Init();
    phinited = 1;
  }
}

void ThreadCache::InitTSD() {
  ASSERT(!tsd_inited_);
  perftools_pthread_key_create(&heap_key_, DestroyThreadCache);
  tsd_inited_ = true;

#ifdef PTHREADS_CRASHES_IF_RUN_TOO_EARLY
  // We may have used a fake pthread_t for the main thread.  Fix it.
  pthread_t zero;
  memset(&zero, 0, sizeof(zero));
  SpinLockHolder h(Static::pageheap_lock());
  for (ThreadCache* h = thread_heaps_; h != NULL; h = h->next_) {
    if (h->tid_ == zero) {
      h->tid_ = pthread_self();
    }
  }
#endif
}

ThreadCache* ThreadCache::CreateCacheIfNecessary() {
  // Initialize per-thread data if necessary
  ThreadCache* heap = NULL;
  {
    SpinLockHolder h(Static::pageheap_lock());
    // On some old glibc's, and on freebsd's libc (as of freebsd 8.1),
    // calling pthread routines (even pthread_self) too early could
    // cause a segfault.  Since we can call pthreads quite early, we
    // have to protect against that in such situations by making a
    // 'fake' pthread.  This is not ideal since it doesn't work well
    // when linking tcmalloc statically with apps that create threads
    // before main, so we only do it if we have to.
#ifdef PTHREADS_CRASHES_IF_RUN_TOO_EARLY
    pthread_t me;
    if (!tsd_inited_) {
      memset(&me, 0, sizeof(me));
    } else {
      me = pthread_self();
    }
#else
    const pthread_t me = pthread_self();
#endif

    // This may be a recursive malloc call from pthread_setspecific()
    // In that case, the heap for this thread has already been created
    // and added to the linked list.  So we search for that first.
    for (ThreadCache* h = thread_heaps_; h != NULL; h = h->next_) {
      if (h->tid_ == me) {
        heap = h;
        break;
      }
    }

    if (heap == NULL) heap = NewHeap(me);
  }

  // We call pthread_setspecific() outside the lock because it may
  // call malloc() recursively.  We check for the recursive call using
  // the "in_setspecific_" flag so that we can avoid calling
  // pthread_setspecific() if we are already inside pthread_setspecific().
  if (!heap->in_setspecific_ && tsd_inited_) {
    heap->in_setspecific_ = true;
    perftools_pthread_setspecific(heap_key_, heap);
#ifdef HAVE_TLS
    // Also keep a copy in __thread for faster retrieval
    threadlocal_heap_ = heap;
#endif
    heap->in_setspecific_ = false;
  }
  return heap;
}

ThreadCache* ThreadCache::NewHeap(pthread_t tid) {
  // Create the heap and add it to the linked list
  ThreadCache *heap = threadcache_allocator.New();
  heap->Init(tid);
  heap->next_ = thread_heaps_;
  heap->prev_ = NULL;
  if (thread_heaps_ != NULL) {
    thread_heaps_->prev_ = heap;
  } else {
    // This is the only thread heap at the momment.
    ASSERT(next_memory_steal_ == NULL);
    next_memory_steal_ = heap;
  }
  thread_heaps_ = heap;
  thread_heap_count_++;
  return heap;
}

void ThreadCache::BecomeIdle() {
  if (!tsd_inited_) return;              // No caches yet
  ThreadCache* heap = GetThreadHeap();
  if (heap == NULL) return;             // No thread cache to remove
  if (heap->in_setspecific_) return;    // Do not disturb the active caller

  heap->in_setspecific_ = true;
  perftools_pthread_setspecific(heap_key_, NULL);
#ifdef HAVE_TLS
  // Also update the copy in __thread
  threadlocal_heap_ = NULL;
#endif
  heap->in_setspecific_ = false;
  if (GetThreadHeap() == heap) {
    // Somehow heap got reinstated by a recursive call to malloc
    // from pthread_setspecific.  We give up in this case.
    return;
  }

  // We can now get rid of the heap
  DeleteCache(heap);
}

void ThreadCache::DestroyThreadCache(void* ptr) {
  // Note that "ptr" cannot be NULL since pthread promises not
  // to invoke the destructor on NULL values, but for safety,
  // we check anyway.
  if (ptr == NULL) return;
#ifdef HAVE_TLS
  // Prevent fast path of GetThreadHeap() from returning heap.
  threadlocal_heap_ = NULL;
#endif
  DeleteCache(reinterpret_cast<ThreadCache*>(ptr));
}

void ThreadCache::DeleteCache(ThreadCache* heap) {
  // Remove all memory from heap
  heap->Cleanup();

  // Remove from linked list
  SpinLockHolder h(Static::pageheap_lock());
  if (heap->next_ != NULL) heap->next_->prev_ = heap->prev_;
  if (heap->prev_ != NULL) heap->prev_->next_ = heap->next_;
  if (thread_heaps_ == heap) thread_heaps_ = heap->next_;
  thread_heap_count_--;

  if (next_memory_steal_ == heap) next_memory_steal_ = heap->next_;
  if (next_memory_steal_ == NULL) next_memory_steal_ = thread_heaps_;
  unclaimed_cache_space_ += heap->max_size_;

  threadcache_allocator.Delete(heap);
}

void ThreadCache::RecomputePerThreadCacheSize() {
  // Divide available space across threads
  int n = thread_heap_count_ > 0 ? thread_heap_count_ : 1;
  size_t space = overall_thread_cache_size_ / n;

  // Limit to allowed range
  if (space < kMinThreadCacheSize) space = kMinThreadCacheSize;
  if (space > kMaxThreadCacheSize) space = kMaxThreadCacheSize;

  double ratio = space / max<double>(1, per_thread_cache_size_);
  size_t claimed = 0;
  for (ThreadCache* h = thread_heaps_; h != NULL; h = h->next_) {
    // Increasing the total cache size should not circumvent the
    // slow-start growth of max_size_.
    if (ratio < 1.0) {
        h->max_size_ = static_cast<size_t>(h->max_size_ * ratio);
    }
    claimed += h->max_size_;
  }
  unclaimed_cache_space_ = overall_thread_cache_size_ - claimed;
  per_thread_cache_size_ = space;
}

void ThreadCache::GetThreadStats(uint64_t* total_bytes, uint64_t* class_count) {
  for (ThreadCache* h = thread_heaps_; h != NULL; h = h->next_) {
    *total_bytes += h->Size();
    if (class_count) {
      for (int cl = 0; cl < kNumClasses; ++cl) {
        class_count[cl] += h->freelist_length(cl);
      }
    }
  }
}

void ThreadCache::set_overall_thread_cache_size(size_t new_size) {
  // Clip the value to a reasonable range
  if (new_size < kMinThreadCacheSize) new_size = kMinThreadCacheSize;
  if (new_size > (1<<30)) new_size = (1<<30);     // Limit to 1GB
  overall_thread_cache_size_ = new_size;

  RecomputePerThreadCacheSize();
}

}  // namespace tcmalloc

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