TIP 494: More use of size_t in Tcl 9

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FlightAware bounty program for improvements to Tcl and certain Tcl packages.
Author:         Jan Nijtmans <jan.nijtmans@gmail.com>
State:          Draft
Type:           Project
Vote:           Pending
Created:        29-Dec-2017
Post-History:
Keywords:       tcl
Tcl-Version:    9.0

Abstract

This TIP describes the non-controversial part of the Tcl 9 changes: Make Tcl 9 ready for the 64-bit era.

Rationale

Many Tcl API functions and struct fields have int parameters, which don't provide sufficient room on 64-bit platforms.

Proposal

  • Enhance the hash functions, such that the hash value is stored in a size_t in stead of unsigned int. This allows hash tables to grow beyond 4Gb on 64-bit platforms

  • Enhance all struct fields representing refCounts or epochs, make them of type size_t

  • All memory-related functions, such as Tcl_Alloc(), will change its size argument from int to size_t, and its "char *" arguments to "void *"

  • Many functions, which have size parameters of type int (but NOT int *) will change to type size_t

  • On 32-bit platforms, this is all 100% upwards binary compatible, provided no internal API is used (since some internal structs has incompatible but externally invisible changes)

  • On 64-bit platforms, those changes cause binary incompatibility, but source compatibility is retained. Therefore the TCL_MAGIC value needs to change, so extensions compiled using Tcl 9 headers will not load in Tcl 8 and reverse.

TODO explain changes in more detail.

Implementation

An implementation of this TIP can be found in the memory-API branch. (still in development)

Copyright

This document has been placed in the public domain.