Migrating from Earlier Versions

Appweb 4 to 8 are highly compatible. Code written for Appweb 4 to 6 should migrate to Appweb 8 with few changes required.

If you are migrating from Appweb 1-3, you should regard Appweb latest as a next generation web server. You can migrate code from Appweb 1-3 to Appweb latest, however, you should anticipate significant refactoring work in the transition, especially with regard to memory allocations.

Migrating to Appweb 9

Appweb 8 adds support for the FastCGI protocol and HTTP Proxies. Appweb 9 is API compatible with Appweb 8. Appweb 9 has improved and optimized pipeline processing and so the timing of certain operations may be modified. Applications, handlers and filters should need very little refactoring to work with Appweb 9.

Migrating to Appweb 8

Appweb 8 adds support for the HTTP/2 protocol. HTTP/2 is a higher performance binary protocol that supports multiplexing multiple request streams over a single network connection. This necessitates some API changes and so applications, handlers and filters may need some minor refactoring to work with Appweb 8. See the separate document Migrating to Appweb 8 for details.

Changes in Appweb 7

Appweb 7 removes deprecated APIs and contains bug fixes. There are no major new features.

Changes in Appweb 6

Appweb 6 APIs are substantially compatible with Appweb 4-5, though previously deprecated APIs have been removed.

Changes in Appweb 5

Appweb 5 APIs are substantially compatible with Appweb 4, though previously deprecated APIs have been removed. The following new capabilities were added for Appweb 5.

Appweb 4.6+ and Appweb 5 use the MakeMe build system. New configure options and cross compiling capabilities have been added. See more details below in MakeMe Changes.

Changes in Appweb 4

Appweb 4 provides equivalent or greater functionality to that in Appweb 3. While Appweb 4 may have a different interface or API, the capabilities of Appweb 3 have been continued in Appweb 4, and in many cases, the features have been enhanced. See the separate document Migrating to Appweb 4 for details.

The following new capabilities have been added to Appweb 4 (and have no equivalent in Appweb 3). These additions should not require adjustment for applications developed under Appweb 3.

The following capabilities have been changed and may impact your Appweb 3 applications.

When migrating from an Appweb version that used Bit for building, please not the following changes:

Memory Allocator

Appweb version 4 to 8 include a high performance memory allocator and generational garbage collector. The allocator is a fast and immediate coalescing allocator. It is optimized for frequent allocations of small blocks and uses a background collector to free unused memory. If you are upgrading from Appweb 1-3, you will need to change how you are doing memory allocations.

The garbage collector is somewhat unusual in a C program. However, garbage collection is especially well suited to long running applications like a web server since it virtually eliminates memory leaks. Unlike traditional memory allocation where free must be called, Appweb 4 uses the opposite approach: memory that must be retained needs to be actively managed to prevent garbage collection. This means that a managed reference must be held for all active memory. See Memory Allocation for more details.

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