After establishing how I\/O affects startup<\/a> and exploring some ways to improve the situation<\/a>, I wanted to check another obvious, yet not so practical for Mozilla, way of reducing startup I\/O.<\/p>\n Firefox is a quite featured web browser, and fortunately, all the code in the Firefox tree doesn't come from Mozilla (though a large part does). Some parts of the code actually come from third party libraries, such as libpng for PNG support, libjpeg for (obviously) JPEG support, libsqlite3 for SQLite support (used, for example, for the awesomebar), or libcairo for part of the layout rendering.<\/p>\n Some of these libraries are also used in other software. For instance, Gtk+, the widget toolkit Firefox uses on UNIX systems, and used by the GNOME desktop environment, needs, directly or indirectly, libcairo for rendering, and libpng for icons. But these other softwares don't embed their own copy of the libraries: they use shared, system libraries.<\/p>\n There are several advantages doing so: they reduce memory footprint, because the library is loaded only once in memory (modulo relocations on data sections), they reduce maintenance overhead (you only need to update one copy for stability or security issues), and, you should have guessed where I'm going by now, they help reduce startup I\/O: a system library that has been loaded by some other software doesn't need to be read from disk again when you start another application using the same system library.<\/p>\n Unfortunately, Mozilla distributes binaries that can run on a large variety of systems, which are not necessarily using the right versions of the libraries, and sometimes even, Mozilla patches some libraries it embeds to fix bugs or add features. One such example, the worst case, actually, is libpng, which is patched to handle APNG files. Libcairo also comes with some bug fixes, most of which, after a while, end up in the original libcairo. Anyways, as Mozilla can't really control which version of cairo, sqlite, etc. are installed on systems where Firefox is going to be used, the only way that works for us is to ship binaries that link against these internal (possibly modified) libraries.<\/p>\n Though the same logic could be applied to some other libraries which we do link against system versions of (such as Gtk+), they're, in practice, not so much a problem as sqlite and cairo, which are the most problematic libraries at the moment.<\/p>\n On non GNU\/Linux platforms (excluding some other uncommon unix variants for Firefox users), system libraries are unfortunately not a common practice, and even if they were, most of the libraries Firefox uses internally are not shipped with the system. On (more or less) controlled environments, however, the story is slightly different. When you know what version of which libraries is shipped, it's easier to start using system libraries. GNU\/Linux distributions are such environments, mobile OS (Android, Maemo\/Meego) are, too.<\/p>\n I'm not interested in discussing here the support implications of GNU\/Linux distributions shipping Firefox binaries linked against system libraries, though in practice, it creates less problems than some people may think. This post only aims at showing how using system libraries impacts startup times, how it could or could not be an interesting thing to investigate on mobile, and how GNU\/Linux distributions practices are actually not hurting.<\/p>\n As a reminder, here are the startup times with a plain Firefox 4.0b8, as collected in previous<\/a> posts<\/a>:<\/p>\n
| <\/th>\n | Average startup time (ms)<\/th>\n<\/tr>\n | ||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| x86<\/th>\n | 3,228.76 \u00c2\u00b1 0.57%<\/td>\n<\/tr>\n | ||||||||||||||||||||||||
| x86-64<\/th>\n | 3,382.0 \u00c2\u00b1 0.51%<\/td>\n<\/tr>\n<\/table>\n The first set of system libraries I enabled are those that the default GNOME desktop environment as it comes in Debian Squeeze uses, except libpng, because the system library doesn't support APNG files (note that I installed libcairo from Debian experimental, as Squeeze doesn't have 1.10):<\/p>\n
|