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Features of the core

Our first task was to reduce the overall size of a statically build interpreter executable (tclsh) and/or interpreter library (libtcl.a). This was realized by making a number of features provided by the standard interpreter optional, i.e removable at will during compile time. With this an end-user of the modularized core is free to remove any features which are not needed by his application and thus to shrink the space required for the executable or library.

The overall set of features which were initially made removable were determined by the requirements of our customer. In other words, we did not spent any time on features possibly giving us a high gain for the effort, but only on features our customer deemed irrelevant for his environment. The details however, i.e. the division of the features named by our customer into the actual removable features, were guided by the results of the discussions the community had had on the newsgroup comp.lang.tcl about this topic [5].

The chosen features are listed in Table 1, together with the C preprocessor macros whose existence will activate the removal of a particular feature. By default none of these macros are defined. Setting the macro MODULAR_TCL will activate all of these macros and thus remove the whole set of features.


Table 1: Removable features
Macro Removed feature
TCL_NO_SOCKETS Channel driver "tcp"
TCL_NO_TTY Channel driver "tty"
TCL_NO_PIPES Channel driver "pipe"
TCL_NO_PIDCMD Command pid
TCL_NO_NONSTDCHAN Creation of channels beyond stdin, stdout and stderr
TCL_NO_CHANNELCOPY Channel copying, C/Tcl, fcopy
TCL_NO_CHANNEL_READ Command read and ``Tcl_ReadChars''
TCL_NO_CHANNEL_EOF Command eof
TCL_NO_CHANNEL_CONFIG Command fconfigure and Tcl_GetChannelOption
TCL_NO_CHANNEL_BLOCKED fblocked
TCL_NO_FILEEVENTS fileevent and underlying APIs
TCL_NO_FILESYSTEM Everything related to the file system
TCL_NO_LOADCMD load and machinery below
TCL_NO_SLAVEINTERP Slave interpreters
TCL_NO_CMDALIASES Command aliases

As Source Navigator crashed when processing the Tcl C sources at that time we decided to conditionalize the code by hand with support by the C compiler. This means that it is possible that we missed code which could have been made optional but currently is not. This may happen especially for a function F which is shared by removable features, and only such. In that case removing all features requiring F will not remove F. This deficiency has to be addressed in the future.

Starting at the topmost function for a feature, usually the function implementing the command to remove we followed the sources and determined the public and non-public non-static functions reachable from this point. After excluding them from the sources through ifdef's a complete build was performed and the compiler log analyzed to find all functions which are actually required by other parts of the core. These functions were made unconditional again. Additional runs of the compiler then allowed us to find all static functions required only by the excluded functionality. These were excluded as well.


next up previous
Next: Comparison of core sizes Up: Experiences with modularizing the Previous: Overview
andreas_kupries@users.sourceforge.net