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

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.

In the past I've also used them to save memory on 64-bit systems with pointer-heavy data structures (using boost.intrusive) using an allocator that operates within a small memory region.

Has something changed within the implementation that makes this restriction necessary?  Was it never supposed to work as I was using it?

There is also an assert that OffsetType is unsigned, which wasn't there before. Maybe I was doing that wrong.

In Christ, Steven Watanabe