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+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+// Extra extensions exported by some malloc implementations.  These
+// extensions are accessed through a virtual base class so an
+// application can link against a malloc that does not implement these
+// extensions, and it will get default versions that do nothing.
+//
+// NOTE FOR C USERS: If you wish to use this functionality from within
+// a C program, see malloc_extension_c.h.
+
+#ifndef ABSL_BASE_INTERNAL_MALLOC_EXTENSION_H_
+#define ABSL_BASE_INTERNAL_MALLOC_EXTENSION_H_
+
+#include <atomic>
+#include <map>
+#include <memory>
+#include <vector>
+
+#include <stddef.h>
+#include <stdint.h>
+#include <string>
+#include "absl/base/macros.h"
+#include "absl/base/port.h"
+namespace absl {
+namespace base_internal {
+
+class MallocExtensionWriter;
+
+// Interface to a pluggable system allocator.
+class SysAllocator {
+ public:
+  SysAllocator() {
+  }
+  virtual ~SysAllocator();
+
+  // Allocates "size"-byte of memory from system aligned with "alignment".
+  // Returns null if failed. Otherwise, the returned pointer p up to and
+  // including (p + actual_size -1) have been allocated.
+  virtual void* Alloc(size_t size, size_t *actual_size, size_t alignment) = 0;
+
+  // Get a human-readable description of the current state of the
+  // allocator.  The state is stored as a null-terminated std::string in
+  // a prefix of buffer.
+  virtual void GetStats(char* buffer, int length);
+};
+
+// The default implementations of the following routines do nothing.
+// All implementations should be thread-safe; the current ones
+// (DebugMallocImplementation and TCMallocImplementation) are.
+class MallocExtension {
+ public:
+  virtual ~MallocExtension();
+
+  // Verifies that all blocks are valid.  Returns true if all are; dumps
+  // core otherwise.  A no-op except in debug mode.  Even in debug mode,
+  // they may not do any checking except with certain malloc
+  // implementations.  Thread-safe.
+  virtual bool VerifyAllMemory();
+
+  // Verifies that p was returned by new, has not been deleted, and is
+  // valid.  Returns true if p is good; dumps core otherwise.  A no-op
+  // except in debug mode.  Even in debug mode, may not do any checking
+  // except with certain malloc implementations.  Thread-safe.
+  virtual bool VerifyNewMemory(const void* p);
+
+  // Verifies that p was returned by new[], has not been deleted, and is
+  // valid.  Returns true if p is good; dumps core otherwise.  A no-op
+  // except in debug mode.  Even in debug mode, may not do any checking
+  // except with certain malloc implementations.  Thread-safe.
+  virtual bool VerifyArrayNewMemory(const void* p);
+
+  // Verifies that p was returned by malloc, has not been freed, and is
+  // valid.  Returns true if p is good; dumps core otherwise.  A no-op
+  // except in debug mode.  Even in debug mode, may not do any checking
+  // except with certain malloc implementations.  Thread-safe.
+  virtual bool VerifyMallocMemory(const void* p);
+
+  // If statistics collection is enabled, sets *blocks to be the number of
+  // currently allocated blocks, sets *total to be the total size allocated
+  // over all blocks, sets histogram[n] to be the number of blocks with
+  // size between 2^n-1 and 2^(n+1), and returns true.  Returns false, and
+  // does not change *blocks, *total, or *histogram, if statistics
+  // collection is disabled.
+  //
+  // Note that these statistics reflect memory allocated by new, new[],
+  // malloc(), and realloc(), but not mmap().  They may be larger (if not
+  // all pages have been written to) or smaller (if pages have been
+  // allocated by mmap()) than the total RSS size.  They will always be
+  // smaller than the total virtual memory size.
+  static constexpr int kMallocHistogramSize = 64;
+  virtual bool MallocMemoryStats(int* blocks, size_t* total,
+                                 int histogram[kMallocHistogramSize]);
+
+  // Get a human readable description of the current state of the malloc
+  // data structures.  The state is stored as a null-terminated std::string
+  // in a prefix of "buffer[0,buffer_length-1]".
+  // REQUIRES: buffer_length > 0.
+  virtual void GetStats(char* buffer, int buffer_length);
+
+  // Outputs to "writer" a sample of live objects and the stack traces
+  // that allocated these objects. The output can be passed to pprof.
+  virtual void GetHeapSample(MallocExtensionWriter* writer);
+
+  // Outputs to "writer" the stack traces that caused growth in the
+  // address space size. The output can be passed to "pprof".
+  virtual void GetHeapGrowthStacks(MallocExtensionWriter* writer);
+
+  // Outputs to "writer" a fragmentation profile. The output can be
+  // passed to "pprof".  In particular, the result is a list of
+  // <n,total,stacktrace> tuples that says that "total" bytes in "n"
+  // objects are currently unusable because of fragmentation caused by
+  // an allocation with the specified "stacktrace".
+  virtual void GetFragmentationProfile(MallocExtensionWriter* writer);
+
+  // -------------------------------------------------------------------
+  // Control operations for getting and setting malloc implementation
+  // specific parameters.  Some currently useful properties:
+  //
+  // generic
+  // -------
+  // "generic.current_allocated_bytes"
+  //      Number of bytes currently allocated by application
+  //      This property is not writable.
+  //
+  // "generic.heap_size"
+  //      Number of bytes in the heap ==
+  //            current_allocated_bytes +
+  //            fragmentation +
+  //            freed memory regions
+  //      This property is not writable.
+  //
+  // tcmalloc
+  // --------
+  // "tcmalloc.max_total_thread_cache_bytes"
+  //      Upper limit on total number of bytes stored across all
+  //      per-thread caches.  Default: 16MB.
+  //
+  // "tcmalloc.current_total_thread_cache_bytes"
+  //      Number of bytes used across all thread caches.
+  //      This property is not writable.
+  //
+  // "tcmalloc.pageheap_free_bytes"
+  //      Number of bytes in free, mapped pages in page heap.  These
+  //      bytes can be used to fulfill allocation requests.  They
+  //      always count towards virtual memory usage, and unless the
+  //      underlying memory is swapped out by the OS, they also count
+  //      towards physical memory usage.  This property is not writable.
+  //
+  // "tcmalloc.pageheap_unmapped_bytes"
+  //      Number of bytes in free, unmapped pages in page heap.
+  //      These are bytes that have been released back to the OS,
+  //      possibly by one of the MallocExtension "Release" calls.
+  //      They can be used to fulfill allocation requests, but
+  //      typically incur a page fault.  They always count towards
+  //      virtual memory usage, and depending on the OS, typically
+  //      do not count towards physical memory usage.  This property
+  //      is not writable.
+  //
+  //  "tcmalloc.per_cpu_caches_active"
+  //      Whether tcmalloc is using per-CPU caches (1 or 0 respectively).
+  //      This property is not writable.
+  // -------------------------------------------------------------------
+
+  // Get the named "property"'s value.  Returns true if the property
+  // is known.  Returns false if the property is not a valid property
+  // name for the current malloc implementation.
+  // REQUIRES: property != null; value != null
+  virtual bool GetNumericProperty(const char* property, size_t* value);
+
+  // Set the named "property"'s value.  Returns true if the property
+  // is known and writable.  Returns false if the property is not a
+  // valid property name for the current malloc implementation, or
+  // is not writable.
+  // REQUIRES: property != null
+  virtual bool SetNumericProperty(const char* property, size_t value);
+
+  // Mark the current thread as "idle".  This routine may optionally
+  // be called by threads as a hint to the malloc implementation that
+  // any thread-specific resources should be released.  Note: this may
+  // be an expensive routine, so it should not be called too often.
+  //
+  // Also, if the code that calls this routine will go to sleep for
+  // a while, it should take care to not allocate anything between
+  // the call to this routine and the beginning of the sleep.
+  //
+  // Most malloc implementations ignore this routine.
+  virtual void MarkThreadIdle();
+
+  // Mark the current thread as "busy".  This routine should be
+  // called after MarkThreadIdle() if the thread will now do more
+  // work.  If this method is not called, performance may suffer.
+  //
+  // Most malloc implementations ignore this routine.
+  virtual void MarkThreadBusy();
+
+  // Attempt to free any resources associated with cpu <cpu> (in the sense
+  // of only being usable from that CPU.)  Returns the number of bytes
+  // previously assigned to "cpu" that were freed.  Safe to call from
+  // any processor, not just <cpu>.
+  //
+  // Most malloc implementations ignore this routine (known exceptions:
+  // tcmalloc with --tcmalloc_per_cpu_caches=true.)
+  virtual size_t ReleaseCPUMemory(int cpu);
+
+  // Gets the system allocator used by the malloc extension instance. Returns
+  // null for malloc implementations that do not support pluggable system
+  // allocators.
+  virtual SysAllocator* GetSystemAllocator();
+
+  // Sets the system allocator to the specified.
+  //
+  // Users could register their own system allocators for malloc implementation
+  // that supports pluggable system allocators, such as TCMalloc, by doing:
+  //   alloc = new MyOwnSysAllocator();
+  //   MallocExtension::instance()->SetSystemAllocator(alloc);
+  // It's up to users whether to fall back (recommended) to the default
+  // system allocator (use GetSystemAllocator() above) or not. The caller is
+  // responsible to any necessary locking.
+  // See tcmalloc/system-alloc.h for the interface and
+  //     tcmalloc/memfs_malloc.cc for the examples.
+  //
+  // It's a no-op for malloc implementations that do not support pluggable
+  // system allocators.
+  virtual void SetSystemAllocator(SysAllocator *a);
+
+  // Try to release num_bytes of free memory back to the operating
+  // system for reuse.  Use this extension with caution -- to get this
+  // memory back may require faulting pages back in by the OS, and
+  // that may be slow.  (Currently only implemented in tcmalloc.)
+  virtual void ReleaseToSystem(size_t num_bytes);
+
+  // Same as ReleaseToSystem() but release as much memory as possible.
+  virtual void ReleaseFreeMemory();
+
+  // Sets the rate at which we release unused memory to the system.
+  // Zero means we never release memory back to the system.  Increase
+  // this flag to return memory faster; decrease it to return memory
+  // slower.  Reasonable rates are in the range [0,10].  (Currently
+  // only implemented in tcmalloc).
+  virtual void SetMemoryReleaseRate(double rate);
+
+  // Gets the release rate.  Returns a value < 0 if unknown.
+  virtual double GetMemoryReleaseRate();
+
+  // Returns the estimated number of bytes that will be allocated for
+  // a request of "size" bytes.  This is an estimate: an allocation of
+  // SIZE bytes may reserve more bytes, but will never reserve less.
+  // (Currently only implemented in tcmalloc, other implementations
+  // always return SIZE.)
+  // This is equivalent to malloc_good_size() in OS X.
+  virtual size_t GetEstimatedAllocatedSize(size_t size);
+
+  // Returns the actual number N of bytes reserved by tcmalloc for the
+  // pointer p.  This number may be equal to or greater than the
+  // number of bytes requested when p was allocated.
+  //
+  // This routine is just useful for statistics collection.  The
+  // client must *not* read or write from the extra bytes that are
+  // indicated by this call.
+  //
+  // Example, suppose the client gets memory by calling
+  //    p = malloc(10)
+  // and GetAllocatedSize(p) returns 16.  The client must only use the
+  // first 10 bytes p[0..9], and not attempt to read or write p[10..15].
+  //
+  // p must have been allocated by this malloc implementation, must
+  // not be an interior pointer -- that is, must be exactly the
+  // pointer returned to by malloc() et al., not some offset from that
+  // -- and should not have been freed yet.  p may be null.
+  // (Currently only implemented in tcmalloc; other implementations
+  // will return 0.)
+  virtual size_t GetAllocatedSize(const void* p);
+
+  // Returns kOwned if this malloc implementation allocated the memory
+  // pointed to by p, or kNotOwned if some other malloc implementation
+  // allocated it or p is null.  May also return kUnknownOwnership if
+  // the malloc implementation does not keep track of ownership.
+  // REQUIRES: p must be a value returned from a previous call to
+  // malloc(), calloc(), realloc(), memalign(), posix_memalign(),
+  // valloc(), pvalloc(), new, or new[], and must refer to memory that
+  // is currently allocated (so, for instance, you should not pass in
+  // a pointer after having called free() on it).
+  enum Ownership {
+    // NOTE: Enum values MUST be kept in sync with the version in
+    // malloc_extension_c.h
+    kUnknownOwnership = 0,
+    kOwned,
+    kNotOwned
+  };
+  virtual Ownership GetOwnership(const void* p);
+
+  // The current malloc implementation.  Always non-null.
+  static MallocExtension* instance() {
+    InitModuleOnce();
+    return current_instance_.load(std::memory_order_acquire);
+  }
+
+  // Change the malloc implementation.  Typically called by the
+  // malloc implementation during initialization.
+  static void Register(MallocExtension* implementation);
+
+  // Type used by GetProperties.  See comment on GetProperties.
+  struct Property {
+    size_t value;
+    // Stores breakdown of the property value bucketed by object size.
+    struct Bucket {
+      size_t min_object_size;
+      size_t max_object_size;
+      size_t size;
+    };
+    // Empty unless detailed info was asked for and this type has buckets
+    std::vector<Bucket> buckets;
+  };
+
+  // Type used by GetProperties.  See comment on GetProperties.
+  enum StatLevel { kSummary, kDetailed };
+
+  // Stores in *result detailed statistics about the malloc
+  // implementation. *result will be a map keyed by the name of
+  // the statistic. Each statistic has at least a "value" field.
+  //
+  // Some statistics may also contain an array of buckets if
+  // level==kDetailed and the "value" can be subdivided
+  // into different buckets for different object sizes.  If
+  // such detailed statistics are not available, Property::buckets
+  // will be empty.  Otherwise Property::buckets will contain
+  // potentially many entries.  For each bucket b, b.value
+  // will count the value contributed by objects in the range
+  // [b.min_object_size, b.max_object_size].
+  //
+  // Common across malloc implementations:
+  //  generic.bytes_in_use_by_app  -- Bytes currently in use by application
+  //  generic.physical_memory_used -- Overall (including malloc internals)
+  //  generic.virtual_memory_used  -- Overall (including malloc internals)
+  //
+  // Tcmalloc specific properties
+  //  tcmalloc.cpu_free            -- Bytes in per-cpu free-lists
+  //  tcmalloc.thread_cache_free   -- Bytes in per-thread free-lists
+  //  tcmalloc.transfer_cache      -- Bytes in cross-thread transfer caches
+  //  tcmalloc.central_cache_free  -- Bytes in central cache
+  //  tcmalloc.page_heap_free      -- Bytes in page heap
+  //  tcmalloc.page_heap_unmapped  -- Bytes in page heap (no backing phys. mem)
+  //  tcmalloc.metadata_bytes      -- Used by internal data structures
+  //  tcmalloc.thread_cache_count  -- Number of thread caches in use
+  //
+  // Debug allocator
+  //  debug.free_queue             -- Recently freed objects
+  virtual void GetProperties(StatLevel level,
+                             std::map<std::string, Property>* result);
+ private:
+  static MallocExtension* InitModule();
+
+  static void InitModuleOnce() {
+    // Pointer stored here so heap leak checker will consider the default
+    // instance reachable, even if current_instance_ is later overridden by
+    // MallocExtension::Register().
+    ABSL_ATTRIBUTE_UNUSED static MallocExtension* default_instance =
+        InitModule();
+  }
+
+  static std::atomic<MallocExtension*> current_instance_;
+};
+
+// Base class than can handle output generated by GetHeapSample() and
+// GetHeapGrowthStacks().  Use the available subclass or roll your
+// own.  Useful if you want explicit control over the type of output
+// buffer used (e.g. IOBuffer, Cord, etc.)
+class MallocExtensionWriter {
+ public:
+  virtual ~MallocExtensionWriter() {}
+  virtual void Write(const char* buf, int len) = 0;
+ protected:
+  MallocExtensionWriter() {}
+  MallocExtensionWriter(const MallocExtensionWriter&) = delete;
+  MallocExtensionWriter& operator=(const MallocExtensionWriter&) = delete;
+};
+
+// A subclass that writes to the std::string "out".  NOTE: The generated
+// data is *appended* to "*out".  I.e., the old contents of "*out" are
+// preserved.
+class StringMallocExtensionWriter : public MallocExtensionWriter {
+ public:
+  explicit StringMallocExtensionWriter(std::string* out) : out_(out) {}
+  virtual void Write(const char* buf, int len) {
+    out_->append(buf, len);
+  }
+
+ private:
+  std::string* const out_;
+  StringMallocExtensionWriter(const StringMallocExtensionWriter&) = delete;
+  StringMallocExtensionWriter& operator=(const StringMallocExtensionWriter&) =
+      delete;
+};
+
+}  // namespace base_internal
+}  // namespace absl
+
+// The nallocx function allocates no memory, but it performs the same size
+// computation as the malloc function, and returns the real size of the
+// allocation that would result from the equivalent malloc function call.
+// Default weak implementation returns size unchanged, but tcmalloc overrides it
+// and returns rounded up size. See the following link for details:
+// http://www.unix.com/man-page/freebsd/3/nallocx/
+extern "C" size_t nallocx(size_t size, int flags);
+
+#ifndef MALLOCX_LG_ALIGN
+#define MALLOCX_LG_ALIGN(la) (la)
+#endif
+
+#endif  // ABSL_BASE_INTERNAL_MALLOC_EXTENSION_H_