cds::memory::michael::opt::check_bounds< Type > Struct Template Reference

Option setter for bounds checking. More...

#include <cds/memory/michael/options.h>

Detailed Description

template<typename Type>
struct cds::memory::michael::opt::check_bounds< Type >

Option setter for bounds checking.

This option defines a strategy to check upper memory boundary of allocated blocks. Type defines a class for bound checking with following interface:

class bound_checker
{
public:
    enum {
        trailer_size = numeric_const
    };

    void make_trailer( void * pStartArea, void * pEndBlock, size_t nAllocSize ) ;
    bool check_bounds( void * pStartArea, void * pEndBlock, size_t nBlockSize ) ;
}

Before allocating a memory block of size N, the heap adds the trailer_size to N and really it allocates N + trailer_size bytes. Then, the heap calls make_trailer function of bound checker with arguments:

• pStartArea - start of allocated block
• pEndBlock - the first byte after really allocated block;

  pEndBlock - pStartArea >= N + trailer_size 

• nAllocSize - requested size in bytes (i.e. N) So, make_trailer function can place some predefined value called bound mark of any type, for example, int64, on address pStartArea + nAllocSize, and store real allocated block size N to pEndBlock - sizeof(size_t). In this example, trailer_size constant is equal sizeof(int64) + sizeof(size_t).

Before the memory block previously allocated is deallocating, the check_bounds function is called. The function has similar signature:

• pStartArea - start of allocated block (like make_trailer fist argument)
• pEndBlock - the first byte after allocated block (like make_trailer second argument)
• nBlockSize - real allocated block size, not equal to nAllocSize argument of make_trailer

The function can:

• calculate real allocated block size:

  N = *reinterpret_cast<size_t>(pEndBlock - sizeof(size_t)) 

• check whether the bound mark is unchanged:

  *reinterpret_cast<int64>(pStartArea + N) == bound_mark 

• if it is not equal - make assertion

The library provides the following predefined bound checkers, i.e they are possible values of Type template argument:

• cds::opt::none - no bound checking is performed (default)
• michael::debug_bound_checking - an assertion is thrown when memory bound violation is detected. This option is acceptable only in debug mode. For release mode it is equal to cds::opt::none.
• michael::strong_bound_checking - an assertion is thrown in debug mode if memory bound violation is detected; an exception is thrown in release mode.

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The documentation for this struct was generated from the following file:

• cds/memory/michael/options.h