src/system-alloc.h

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// ---
// Author: Sanjay Ghemawat
//
// Routine that uses sbrk/mmap to allocate memory from the system.
// Useful for implementing malloc.

#ifndef TCMALLOC_SYSTEM_ALLOC_H_
#define TCMALLOC_SYSTEM_ALLOC_H_

#include <config.h>
#include <stddef.h>                     // for size_t

class SysAllocator;

// REQUIRES: "alignment" is a power of two or "0" to indicate default alignment
//
// Allocate and return "N" bytes of zeroed memory.
//
// If actual_bytes is NULL then the returned memory is exactly the
// requested size.  If actual bytes is non-NULL then the allocator
// may optionally return more bytes than asked for (i.e. return an
// entire "huge" page if a huge page allocator is in use).
//
// The returned pointer is a multiple of "alignment" if non-zero. The
// returned pointer will always be aligned suitably for holding a
// void*, double, or size_t. In addition, if this platform defines
// CACHELINE_ALIGNED, the return pointer will always be cacheline
// aligned.
//
// Returns NULL when out of memory.
extern PERFTOOLS_DLL_DECL
void* TCMalloc_SystemAlloc(size_t bytes, size_t *actual_bytes,
			   size_t alignment = 0);

// This call is a hint to the operating system that the pages
// contained in the specified range of memory will not be used for a
// while, and can be released for use by other processes or the OS.
// Pages which are released in this way may be destroyed (zeroed) by
// the OS.  The benefit of this function is that it frees memory for
// use by the system, the cost is that the pages are faulted back into
// the address space next time they are touched, which can impact
// performance.  (Only pages fully covered by the memory region will
// be released, partial pages will not.)
//
// Returns false if release failed or not supported.
extern PERFTOOLS_DLL_DECL
bool TCMalloc_SystemRelease(void* start, size_t length);

// Called to ressurect memory which has been previously released
// to the system via TCMalloc_SystemRelease.  An attempt to
// commit a page that is already committed does not cause this
// function to fail.
extern PERFTOOLS_DLL_DECL
void TCMalloc_SystemCommit(void* start, size_t length);

// The current system allocator.
extern PERFTOOLS_DLL_DECL SysAllocator* sys_alloc;

// Number of bytes taken from system.
extern PERFTOOLS_DLL_DECL size_t TCMalloc_SystemTaken;

#endif /* TCMALLOC_SYSTEM_ALLOC_H_ */