path: root/src/thread_cache.h

// -*- Mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*-
// Copyright (c) 2008, Google Inc.
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//
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

// ---
// Author: Sanjay Ghemawat <opensource@google.com>

#ifndef TCMALLOC_THREAD_CACHE_H_
#define TCMALLOC_THREAD_CACHE_H_

#include <config.h>
#include <atomic>
#include <stddef.h>                     // for size_t, NULL
#include <stdint.h>                     // for uint32_t, uint64_t
#include <sys/types.h>                  // for ssize_t
#include "base/commandlineflags.h"
#include "base/threading.h"
#include "common.h"
#include "linked_list.h"
#include "page_heap_allocator.h"
#include "sampler.h"
#include "static_vars.h"

#include "common.h"            // for SizeMap, kMaxSize, etc
#include "internal_logging.h"  // for ASSERT, etc
#include "linked_list.h"       // for SLL_Pop, SLL_PopRange, etc
#include "page_heap_allocator.h"  // for PageHeapAllocator
#include "sampler.h"           // for Sampler
#include "static_vars.h"       // for Static

DECLARE_int64(tcmalloc_sample_parameter);

namespace tcmalloc {

//-------------------------------------------------------------------
// Data kept per thread
//-------------------------------------------------------------------

class ThreadCache {
 public:
  // Allocate a new heap. REQUIRES: Static::pageheap_lock is not held.
  static ThreadCache* NewHeap();
  // REQUIRES: Static::pageheap_lock is not held.
  static void DeleteCache(ThreadCache* heap);

  // REQUIRES: Static::pageheap_lock is held
  ThreadCache();
  // REQUIRES: Static::pageheap_lock is not held
  ~ThreadCache();

  // Accessors (mostly just for printing stats)
  int freelist_length(uint32_t cl) const { return list_[cl].length(); }

  // Total byte size in cache
  size_t Size() const { return size_; }

  // Allocate an object of the given size and class. The size given
  // must be the same as the size of the class in the size map.
  void* Allocate(size_t size, uint32_t cl, void *(*oom_handler)(size_t size));
  void Deallocate(void* ptr, uint32_t size_class);

  void Scavenge();

  int GetSamplePeriod();

  // Record allocation of "k" bytes.  Return true iff allocation
  // should be sampled
  bool SampleAllocation(size_t k);

  bool TryRecordAllocationFast(size_t k);

  static void         InitModule();

  // Return the number of thread heaps in use.
  static inline int HeapsInUse();

  // Adds to *total_bytes the total number of bytes used by all thread heaps.
  // Also, if class_count is not NULL, it must be an array of size kNumClasses,
  // and this function will increment each element of class_count by the number
  // of items in all thread-local freelists of the corresponding size class.
  // REQUIRES: Static::pageheap_lock is held.
  static void GetThreadStats(uint64_t* total_bytes, uint64_t* class_count);

  // Sets the total thread cache size to new_size, recomputing the
  // individual thread cache sizes as necessary.
  // REQUIRES: Static::pageheap lock is held.
  static void set_overall_thread_cache_size(size_t new_size);
  static size_t overall_thread_cache_size() {
    return overall_thread_cache_size_;
  }

  // Sets the lower bound on per-thread cache size to new_size.
  static void set_min_per_thread_cache_size(size_t new_size) {
    min_per_thread_cache_size_.store(new_size, std::memory_order_relaxed);
  }

  static size_t min_per_thread_cache_size() {
    return min_per_thread_cache_size_.load(std::memory_order_relaxed);
  }

  static int thread_heap_count() {
    return thread_heap_count_;
  }

 private:
  class FreeList {
   private:
    void*    list_;       // Linked list of nodes

#ifdef _LP64
    // On 64-bit hardware, manipulating 16-bit values may be slightly slow.
    uint32_t length_;      // Current length.
    uint32_t lowater_;     // Low water mark for list length.
    uint32_t max_length_;  // Dynamic max list length based on usage.
    // Tracks the number of times a deallocation has caused
    // length_ > max_length_.  After the kMaxOverages'th time, max_length_
    // shrinks and length_overages_ is reset to zero.
    uint32_t length_overages_;
#else
    // If we aren't using 64-bit pointers then pack these into less space.
    uint16_t length_;
    uint16_t lowater_;
    uint16_t max_length_;
    uint16_t length_overages_;
#endif

    int32_t size_;

   public:
    void Init(size_t size) {
      list_ = NULL;
      length_ = 0;
      lowater_ = 0;
      max_length_ = 1;
      length_overages_ = 0;
      size_ = size;
    }

    // Return current length of list
    size_t length() const {
      return length_;
    }

    int32_t object_size() const {
      return size_;
    }

    // Return the maximum length of the list.
    size_t max_length() const {
      return max_length_;
    }

    // Set the maximum length of the list.  If 'new_max' > length(), the
    // client is responsible for removing objects from the list.
    void set_max_length(size_t new_max) {
      max_length_ = new_max;
    }

    // Return the number of times that length() has gone over max_length().
    size_t length_overages() const {
      return length_overages_;
    }

    void set_length_overages(size_t new_count) {
      length_overages_ = new_count;
    }

    // Is list empty?
    bool empty() const {
      return list_ == NULL;
    }

    // Low-water mark management
    int lowwatermark() const { return lowater_; }
    void clear_lowwatermark() { lowater_ = length_; }

    uint32_t Push(void* ptr) {
      uint32_t length = length_ + 1;
      SLL_Push(&list_, ptr);
      length_ = length;
      return length;
    }

    void* Pop() {
      ASSERT(list_ != NULL);
      length_--;
      if (length_ < lowater_) lowater_ = length_;
      return SLL_Pop(&list_);
    }

    bool TryPop(void **rv) {
      if (SLL_TryPop(&list_, rv)) {
        length_--;
        if (PREDICT_FALSE(length_ < lowater_)) lowater_ = length_;
        return true;
      }
      return false;
    }

    void* Next() {
      return SLL_Next(&list_);
    }

    void PushRange(int N, void *start, void *end) {
      SLL_PushRange(&list_, start, end);
      length_ += N;
    }

    void PopRange(int N, void **start, void **end) {
      SLL_PopRange(&list_, N, start, end);
      ASSERT(length_ >= N);
      length_ -= N;
      if (length_ < lowater_) lowater_ = length_;
    }
  };

  // Gets and returns an object from the central cache, and, if possible,
  // also adds some objects of that size class to this thread cache.
  void* FetchFromCentralCache(uint32_t cl, int32_t byte_size,
                              void *(*oom_handler)(size_t size));

  void ListTooLong(void* ptr, uint32_t cl);

  // Releases some number of items from src.  Adjusts the list's max_length
  // to eventually converge on num_objects_to_move(cl).
  void ListTooLong(FreeList* src, uint32_t cl);

  // Releases N items from this thread cache.
  void ReleaseToCentralCache(FreeList* src, uint32_t cl, int N);

  void SetMaxSize(int32_t new_max_size);

  // Increase max_size_ by reducing unclaimed_cache_space_ or by
  // reducing the max_size_ of some other thread.  In both cases,
  // the delta is kStealAmount.
  void IncreaseCacheLimit();
  // Same as above but requires Static::pageheap_lock() is held.
  void IncreaseCacheLimitLocked();

  // Linked list of heap objects.  Protected by Static::pageheap_lock.
  static ThreadCache* thread_heaps_;
  static int thread_heap_count_;

  // A pointer to one of the objects in thread_heaps_.  Represents
  // the next ThreadCache from which a thread over its max_size_ should
  // steal memory limit.  Round-robin through all of the objects in
  // thread_heaps_.  Protected by Static::pageheap_lock.
  static ThreadCache* next_memory_steal_;

  // Lower bound on per thread cache size. Default value is 512 KBs. 
  static std::atomic<size_t> min_per_thread_cache_size_;

  // Overall thread cache size.  Protected by Static::pageheap_lock.
  static size_t overall_thread_cache_size_;

  // Global per-thread cache size.  Writes are protected by
  // Static::pageheap_lock.  Reads are done without any locking, which should be
  // fine as long as size_t can be written atomically and we don't place
  // invariants between this variable and other pieces of state.
  static volatile size_t per_thread_cache_size_;

  // Represents overall_thread_cache_size_ minus the sum of max_size_
  // across all ThreadCaches.  Protected by Static::pageheap_lock.
  static ssize_t unclaimed_cache_space_;

  // This class is laid out with the most frequently used fields
  // first so that hot elements are placed on the same cache line.

  FreeList      list_[kClassSizesMax];     // Array indexed by size-class

  int32_t       size_;                     // Combined size of data
  int32_t       max_size_;                 // size_ > max_size_ --> Scavenge()

  // We sample allocations, biased by the size of the allocation
  Sampler       sampler_;               // A sampler

  static void RecomputePerThreadCacheSize();

  // All ThreadCache objects are kept in a linked list (for stats collection)
  ThreadCache* next_;
  ThreadCache* prev_;

  // Ensure that this class is cacheline-aligned. This is critical for
  // performance, as false sharing would negate many of the benefits
  // of a per-thread cache.
} CACHELINE_ALIGNED;

// Allocator for thread heaps
// This is logically part of the ThreadCache class, but MSVC, at
// least, does not like using ThreadCache as a template argument
// before the class is fully defined.  So we put it outside the class.
extern PageHeapAllocator<ThreadCache> threadcache_allocator;

inline int ThreadCache::HeapsInUse() {
  return threadcache_allocator.inuse();
}

ALWAYS_INLINE void* ThreadCache::Allocate(
  size_t size, uint32_t cl, void *(*oom_handler)(size_t size)) {
  FreeList* list = &list_[cl];

#ifdef NO_TCMALLOC_SAMPLES
  size = list->object_size();
#endif

  ASSERT(size <= kMaxSize);
  ASSERT(size != 0);
  ASSERT(size == 0 || size == Static::sizemap()->ByteSizeForClass(cl));

  void* rv;
  if (!list->TryPop(&rv)) {
    return FetchFromCentralCache(cl, size, oom_handler);
  }
  size_ -= size;
  return rv;
}

ALWAYS_INLINE void ThreadCache::Deallocate(void* ptr, uint32_t cl) {
  ASSERT(list_[cl].max_length() > 0);
  FreeList* list = &list_[cl];

  // This catches back-to-back frees of allocs in the same size
  // class. A more comprehensive (and expensive) test would be to walk
  // the entire freelist. But this might be enough to find some bugs.
  ASSERT(ptr != list->Next());

  uint32_t length = list->Push(ptr);

  if (PREDICT_FALSE(length > list->max_length())) {
    ListTooLong(list, cl);
    return;
  }

  size_ += list->object_size();
  if (PREDICT_FALSE(size_ > max_size_)){
    Scavenge();
  }
}

inline void ThreadCache::SetMaxSize(int32_t new_max_size) {
  max_size_ = new_max_size;
}

#ifndef NO_TCMALLOC_SAMPLES

inline bool ThreadCache::SampleAllocation(size_t k) {
  ASSERT(Static::IsInited());
  return !sampler_.RecordAllocation(k);
}

inline bool ThreadCache::TryRecordAllocationFast(size_t k) {
  ASSERT(Static::IsInited());
  return sampler_.TryRecordAllocationFast(k);
}

#else

inline bool ThreadCache::SampleAllocation(size_t k) {
  return false;
}

inline bool ThreadCache::TryRecordAllocationFast(size_t k) {
  return true;
}

#endif

}  // namespace tcmalloc

#endif  // TCMALLOC_THREAD_CACHE_H_