Re: [boost] [interprocess] 32-bit offset_ptr

On 02/02/2019 18:19, Steven Watanabe via Boost wrote:

AMDG

On 2/2/19 9:28 AM, Phil Endecott via Boost wrote:

...

I have some old code that uses 32-bit offset_ptrs, i.e.

  typedef boost::interprocess::offset_ptr ptr_t;

This has stopped working on 64-bit systems at some point since 1.58. git blame suggests a commit on  14 Oct 2015.  There is now a static assert that checks that OffsetType is at least as large as a raw pointer.

In the current case, I'm using these pointers within memory-mapped files which will always be vastly smaller than the 32-bit limit.  Using 32-bit offsets seemed like a worthwhile optimisation at the time, and now I am hoping to maintain binary compatibility with those files.

The offset_ptr is not restricted to existing inside the memory-mapped file. The library can and does create temporaries.

Correct. An offset_ptr placed in the stack (a temporary, a return or argument in a function) must be able to point to an object in shared memory. Thus in 64 bit address-spaces a 64-bit offset is needed. Best, Ion