ClickHouse/contrib/libtcmalloc/src/heap-profile-stats.h

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// This file defines structs to accumulate memory allocation and deallocation
// counts.  These structs are commonly used for malloc (in HeapProfileTable)
// and mmap (in MemoryRegionMap).

// A bucket is data structure for heap profiling to store a pair of a stack
// trace and counts of (de)allocation.  Buckets are stored in a hash table
// which is declared as "HeapProfileBucket**".
//
// A hash value is computed from a stack trace.  Collision in the hash table
// is resolved by separate chaining with linked lists.  The links in the list
// are implemented with the member "HeapProfileBucket* next".
//
// A structure of a hash table HeapProfileBucket** bucket_table would be like:
// bucket_table[0] => NULL
// bucket_table[1] => HeapProfileBucket() => HeapProfileBucket() => NULL
// ...
// bucket_table[i] => HeapProfileBucket() => NULL
// ...
// bucket_table[n] => HeapProfileBucket() => NULL

#ifndef HEAP_PROFILE_STATS_H_
#define HEAP_PROFILE_STATS_H_

struct HeapProfileStats {
  // Returns true if the two HeapProfileStats are semantically equal.
  bool Equivalent(const HeapProfileStats& other) const {
    return allocs - frees == other.allocs - other.frees &&
        alloc_size - free_size == other.alloc_size - other.free_size;
  }

  int32 allocs;      // Number of allocation calls.
  int32 frees;       // Number of free calls.
  int64 alloc_size;  // Total size of all allocated objects so far.
  int64 free_size;   // Total size of all freed objects so far.
};

// Allocation and deallocation statistics per each stack trace.
struct HeapProfileBucket : public HeapProfileStats {
  // Longest stack trace we record.
  static const int kMaxStackDepth = 32;

  uintptr_t hash;           // Hash value of the stack trace.
  int depth;                // Depth of stack trace.
  const void** stack;       // Stack trace.
  HeapProfileBucket* next;  // Next entry in hash-table.
};

#endif  // HEAP_PROFILE_STATS_H_