### ACE+TAO Subsetting

We are currently subsetting ACE+TAO to make them more flexible and to reduce their footprint for embedded systems. This document describes what we've done thus far, what we're planning to do next, and how to leverage our efforts to minimize the size of your ACE+TAO applications.

Contents

1. Motivation for Splitting ACE into Multiple Libraries
2. Configuration Management
3. Classes in Each ACE Library Subset
4. ACE Library Size Breakdown
5. Building ACE Subsets
6. ACE_OS Adaptation Layer
7. POSIX ACE (PACE)
8. Minimum TAO
9. ACE+TAO Subsetting Work in Progress

### Motivation for Splitting ACE into Multiple Libraries

This document describes how we are splitting ACE into multiple libraries, each of which will contain a smaller subset of the overall ACE functionality. The primary motivations for subsetting ACE are:

- Principle of parsimony -- i.e., developers should incur time/space overhead for components they use, rather than for all the components in the ACE framework.

- Simplify the learning curve -- i.e., developers only need to learn how to program components that they actually use.

The main design goals of our approach are as follows:

1. Support the original libACE as before. Thus, for users who want to use the existing ACE library as is, there will be no changes, i.e., just link with `libACE` as usual.

2. Allow ACE (and TAO) programmers to use smaller subsets of the entire `libACE` library. These subsets will include the following libraries:

   `libACE_OS` -- This library contains the OS adaptation layer and its supporting classes. All other ACE libraries will depend on `libACE_OS` and it will depend on no other ACE libraries.

   `libACE_Utils` -- This library contains the various ACE container classes and other miscellaneous classes, such as Singleton, auto_ptr, timers, etc. This library will depend only on `libACE_OS`.

   `libACE_Logging` -- This library contains the various ACE logging and tracing classes. This library will depend only on `libACE_OS`.

   `libACE_Threads` -- This library contains the ACE thread/process management and synchronization classes. This library will depend only on `libACE_OS`.

   `libACE_Demux` -- This library contains the ACE Reactor and Proactor classes. This library will depend on `libACE_OS` and `libACE_Thread`.

   `libACE_Connection` -- This library contains the ACE Connection components, i.e., Acceptor, Connector, and Svc_Handler. This library will depend on `libACE_OS`, `libACE_Thread`, and `libACE_Demux`.

   `libACE_Sockets` -- This library contains the ACE C++ wrappers for sockets. This library will depend on `libACE_OS`.

   `libACE_IPC` -- This library contains all the ACE C++ wrappers for the other types of IPC and FILE I/O other than sockets. This library will depend on `libACE_OS` and `libACE_Sockets`.

   `libACE_Svcconf` -- This library contains the ACE C++ wrappers for the Service Configurator. This library will depend on `libACE_OS`, `libACE_Demux`, `libACE_Thread`, and `libACE_Sockets`.

   `libACE_Streams` -- This library contains the ACE Streams classes. This library will depend on `libACE_OS`, `libACE_Demux`, and `libACE_Thread`.

   `libACE_Memory` -- This library contains the ACE C++ wrappers for shared memory and memory-mapped files. This library will depend on `libACE_OS`.

   `libACE_Token` -- This library contains the ACE C++ wrappers for token support. This library is not needed by TAO.

   `libACE_Other` -- This library contains miscellaneous code, primarily including a CORBA interface and naming support. It is not actively supported, and is not needed by TAO. Its functionality is included in TAO.

We are also planning to support the OMG's Minimum CORBA specification as part of a separate effort. Preliminary results of prototypes for Minimum CORBA we've integrate to TAO have been very promising, yielding a 40% reduction in ORB footprint.

Note that the ACE library subsets described above are intended as a guideline, not a complete specification. The actual partitioning of files in the final ACE library subsets may differ somewhat to improve footprint and simplify common use-cases.

### Configuration Management

Configuration management for the ACE library subsets described above will be organized as follows:

1. A single source tree with a single "version" for the source tree.

2. Releases of libACE and its "subsets" will be atomic, i.e., all or nothing.

### Classes in Each ACE Library Subset

Below, we describe the classes in each ACE library subset.

#### libACE_OS

This library contains the OS adaptation layer and its supporting classes. The classes in this library should not depend on any other ACE library subsets. All of the other libraries will depend on this library. The following classes are included in this library.

    config.h
    Basic_Types
    OS
    Sched_Params
    Handle_Set

#### libACE_Utils

This library contains the following ACE container classes and other miscellaneous classes.

    ACE
    Active_Map_Manager
    Arg_Shifter
    ARGV
    Containers
    Dirent
    Dynamic
    Filecache
    Functor
    Get_Opt
    Hash_Map_Manager
    High_Res_Timer
    Method_Request
    Object_Manager
    Profile_Timer
    Registry
    SString
    Stats
    System_Time
    Time_Request_Reply
    Timeprobe
    Timer_Hash
    Timer_Heap
    Timer_List
    Timer_Queue
    Timer_Wheel

#### libACE_Logging

This library contains the various ACE logging and tracing classes.

    Dump
    Log_Msg
    Log_Record
    Trace

#### libACE_Threads

This library contains the ACE thread/process management and synchronization classes.

    Activation_Queue
    Process
    Process_Manager
    Synch
    Synch_Options
    Thread
    Thread_Manager
    Token

#### libACE_Demux

This library contains the ACE Reactor and its associated classes, including the ACE Connection components.

    Event_Handler
    POSIX_Proactor
    Priority_Reactor
    Proactor
    Reactor
    Select_Reactor
    Select_Reactor_Base
    WFMO_Reactor

#### libACE_Connection

This library contains the ACE Connection components, i.e., Acceptor, Connector, and Svc_Handler.

    Asynch_IO
    Asynch_IO_Impl
    POSIX_Asynch_IO
    Strategies

#### libACE_Sockets

This library contains the ACE C++ wrappers for sockets.

    IPC_SAP
    LSOCK
    LSOCK_Acceptor
    LSOCK_CODgram
    LSOCK_Connector
    LSOCK_Dgram
    LSOCK_Stream
    SOCK
    SOCK_Acceptor
    SOCK_CODgram
    SOCK_Connector
    SOCK_Dgram
    SOCK_Dgram_Bcast
    SOCK_Dgram_Mcast
    SOCK_IO
    SOCK_Stream

#### libACE_IPC

This library contains all the ACE C++ wrappers for the other types of IPC and FILE I/O other than sockets. This library will depend on the `libACE_Socket` library.

    Addr
    DEV
    DEV_Addr
    DEV_Connector
    DEV_IO
    FIFO
    FIFO_Recv
    FIFO_Recv_Msg
    FIFO_Send
    FIFO_Send_Msg
    FILE_Addr
    FILE
    FILE_Connector
    FILE_IO
    INET_Addr
    IO_SAP
    IOStream
    Pipe
    Signal
    SPIPE_Addr
    SPIPE
    SPIPE_Acceptor
    SPIPE_Connector
    SPIPE_Stream
    SV_Message
    SV_Message_Queue
    SV_Semaphore_Complex
    SV_Semaphore_Simple
    SV_Shared_Memory
    TLI
    TLI_Acceptor
    TLI_Connector
    TLI_Stream
    TTY_IO
    UNIX_Addr
    UPIPE_Acceptor
    UPIPE_Connector
    UPIPE_Stream

#### libACE_Svcconf

This library contains the ACE C++ wrappers for the Service Configurator component.

    DLL
    Parse_Node
    Service_Config
    Service_Manager
    Service_Object
    Service_Repository
    Service_Types
    Shared_Object
    Svc_Conf_l
    Svc_Conf_y

#### libACE_Streams

This library contains the ACE Streams classes.

    CDR_Stream
    Message_Block
    Message_Queue
    Task

#### libACE_Memory

This library contains the ACE C++ wrappers for shared memory and memory-mapped files.

    Malloc
    Mem_Map
    Memory_Pool
    Obstack
    Read_Buffer
    Shared_Memory
    Shared_Memory_MM
    Shared_Memory_SV

#### libACE_Token

This componenty contains the ACE C++ wrappers for Token classes.

    Local_Tokens
    Remote_Tokens
    Token_Collection
    Token_Invariants
    Token_Manager
    Token_Request_Reply

#### libACE_Other

This component contains miscellaneous ACE C++ wrappers.

    CORBA_Handler
    CORBA_Ref
    Local_Name_Space
    Msg_WFMO_Reactor
    Name_Proxy
    Name_Request_Reply
    Name_Space
    Naming_Context
    Registry_Name_Space
    Remote_Name_Space
    TP_Reactor
    XtReactor

### ACE Library Size Breakdown

Here is an example size breakdown, by ACE library component. It is for the ACE 5.0 libACE.a, statically built with these make flags:

        debug=0 optimize=1 static_libs_only=1 DEFFLAGS=-DACE_USE_RCSID=0

These options translate into:

(a) No debugging,
(b) Optimization is set to -O2,
(c) Static ACE and TAO libraries, and
(d) Use of RCS Ids is turned off.

To build an ACE static library, if shared libraries are the default, use `make static_libs_only=1`. If you're using recent versions of GNU GCC, you can use the -frepo option, which typically reduces the footprint by another 25 percent.

Platform | Component | Total | For TAO subset | OS | Utils | Logging | Threads | Demux | Con- nection | Sockets | IPC | Svcconf | Streams | Memory | Token | Other
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Linux (RedHat 6.0/Intel) egcs 2.91.66 | Size, bytes | 648727 | 515501 | 10937 | 118305 | 13544 | 59593 | 74629 | 49933 | 16084 | 34820 | 92192 | 18462 | 27002 | 71574 | 61652
Percentage of total size | 100 | 79.46 | 1.69 | 18.24 | 2.09 | 9.19 | 11.50 | 7.70 | 2.48 | 5.37 | 14.21 | 2.85 | 4.16 | 11.03 | 9.50
LynxOS 3.0.0 g++ 2.7-97r1 | Size, bytes | 582672 | 475216 | 25620 | 97220 | 11000 | 44192 | 71388 | 58100 | 13120 | 31572 | 77972 | 21468 | 23564 | 60832 | 46624
Percentage of total size | 100 | 81.56 | 4.40 | 16.69 | 1.89 | 7.58 | 12.25 | 9.97 | 2.25 | 5.42 | 13.38 | 3.68 | 4.04 | 10.44 | 8.00
SunOS5.7 egcs 2.91.60 | Size, bytes | 709543 | 570693 | 11877 | 115306 | 13721 | 63027 | 87962 | 68551 | 16917 | 42954 | 99839 | 21357 | 29182 | 75970 | 62880
Percentage of total size | 100 | 80.43 | 1.67 | 16.25 | 1.93 | 8.88 | 12.40 | 9.66 | 2.38 | 6.05 | 14.07 | 3.01 | 4.11 | 10.71 | 8.86
SunOS 5.7 GreenHills 1.8.9 | Size, bytes | 803651 | 653787 | 15800 | 146633 | 18544 | 69172 | 103584 | 60580 | 23084 | 52986 | 108200 | 21528 | 33676 | 79324 | 70540
Percentage of total size | 100 | 81.35 | 1.97 | 18.25 | 2.31 | 8.61 | 12.89 | 7.54 | 2.87 | 6.59 | 13.46 | 2.68 | 4.19 | 9.87 | 8.78
SunOS 5.7 Sun C++ 4.2 | Size, bytes | 626824 | 494501 | 15502 | 64929 | 15605 | 63364 | 106841 | 55013 | 19945 | 73584 | 46434 | 19685 | 25952 | 69843 | 62480
Percentage of total size | 100 | 78.89 | 2.47 | 10.36 | 2.49 | 10.11 | 17.04 | 8.78 | 3.18 | 11.74 | 7.41 | 3.14 | 4.14 | 11.14 | 9.97
VxWorks 5.3.1 GreenHills 1.8.8 | Size, bytes | 689564 | 542628 | 22252 | 145036 | 19664 | 63640 | 54296 | 980 | 22120 | 47468 | 117932 | 23220 | 27220 | 78900 | 68036
Percentage of total size | 100 | 78.69 | 3.23 | 21.03 | 2.85 | 9.23 | 7.87 | 0.14 | 3.21 | 6.88 | 17.10 | 3.37 | 3.95 | 11.44 | 9.87
VxWorks 5.3.1 g++ cygnus- 2.7.2-960126 (with implicit templates) | Size, bytes | 1051540 | 888244 | 36484 | 140832 | 14344 | 66740 | 266192 | 14480 | 15084 | 106308 | 142500 | 55932 | 29348 | 88564 | 74732
Percentage of total size | 100 | 84.47 | 3.47 | 13.39 | 1.36 | 6.35 | 25.31 | 1.38 | 1.43 | 10.11 | 13.55 | 5.32 | 2.79 | 8.42 | 7.11

### Building ACE Subsets

By default, the ACE library contains all of the components that ACE currently supports. To reduce build time and library size, you can exclude unused components. To do that, define an `ACE_COMPONENTS` variable using this approach:

1. In your `$(ACE_ROOT)/include/makeinclude/platform_macros.GNU` file, e.g., add:

       ACE_COMPONENTS = OS

   or

2. On the make command line, e.g.,

       make ACE_COMPONENTS=OS

   or

3. Set (and export) the `ACE_COMPONENTS` environment variable to contain the components that you want to build.

Please see `../ace/Makefile` for the default contents of `ACE_COMPONENTS`.

A special value of `ACE_COMPONENTS` can be used to build an ACE library that supports TAO. The special value is `FOR_TAO`. So, for example, you can add this to your `$(ACE_ROOT)/include/makeinclude/platform_macros.GNU` to restrict ACE support to just that which is needed for TAO:

    ACE_COMPONENTS = FOR_TAO

Please note the current limitations:

1. We currently don't check for interdependencies between components. For example, if you build any component beside `OS`, you must explicitly include `OS` in your `ACE_COMPONENTS`.
2. We currently don't check this macro in other ACE or TAO Makefiles, or in their tests. We'll add those checks as time allows.
3. This is only supported by the gmake Makefiles. For example, the MSVC projects on Win32 do not support the specification of components.

### ACE_OS Adaptation Layer

The lowest-level component, `OS`, is also called the ACE_OS adaption layer. It provides the ACE interface to the underlying operating system, but little else. It can be used standalone.

To create the ACE_OS adaptation layer, build your `libACE` with `ACE_COMPONENTS` set to `OS`. In addition, add `#include "ace/config-minimal.h"` to your `ACE_wrappers/ace/config.h` file.

When using the ACE_OS adaptation layer, you'll be limited to the the `ACE_OS` member functions, ACE's Basic_Types and Sched_Params, and macros defined in `ace/OS.h`. See ACE's Basic_Types_Test.cpp for an example of usage.

The POSIX ACE (PACE) project is an OS abstraction layer designed for lightweight and/or verified systems. When complete, it will offer these benefits:

1. A strict POSIX.1-like, low-level interface. Its interface is ``POSIX compatible'' by that we mean as close to POSIX.1 as it can be, given that PACE is not an operating system. To avoid name conflicts with OS APIs, all low-level PACE function names have the `pace_` prefix.

2. The low-level interface is a C file, so that it can be used in both C and C++ programs.

3. The low-level interface is partitioned into multiple files, one per POSIX.1 section, which will help linkers reduce the footprint for statically linked applications.

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