How Equinox load bundles

Equinox launcher is responsible to start OSGi framework. The system bundle would be created and marked as installed when initializing the framework. Equinox also tries to install the installed bundles if finding them in persistence data during the initializing period. Of course there is no extra bundles would be installed when launching Equinox first time.

Then Equinox launcher would install the bundles specified by vm's system property 'osgi.bundles'. And start the initial bundles that are marked as early start. For example, let's have a look at the configuration/config.ini of Eclipse, you would find a line similar as below,
osgi.bundles=reference\:file\:org.eclipse.equinox.simpleconfigurator_1.0.200.v20090831.jar@1\:start
It means the start level of bundle 'org.eclipse.equinox.simpleconfigurator_1.0.200.v20090831.jar' is 1, and it would be started after installing it.

Here you would ask there are only two bundles are installed(one is system bundle 'org.eclipse.osgi', the other is 'org.eclipse.equinox.simpleconfigurator') when launching Equinox, how the other bundles are installed? It's done by the activate method of 'simpleconfigurator' bundle. The available bundles are recorded in plain text file configuration/org.eclipse.equinox.simpleconfigurator/bundles.info, simpleconfigurator read the file then install those bundles.

It's a new bundle management introduced by p2. P2 also supports the traditional way to install extensions, such as link file, .eclipseproduct file and directly copying features/plugins.
Below table lists the p2 bundles to implement the compatibility installation feature,

Bundle

Usage

org.eclipse.equinox.p2.directorywatcher

the definition and implementation of directory watcher API

org.eclipse.equinox.p2.updatesite

the implementation of updatesite repository

org.eclipse.equinox.p2.extensionlocation

the implementation of extension repository

org.eclipse.equinox.p2.reconciler.dropins

scan dropin folder and link files; watch the traditional configuration file used by update manager

P2 reconciler would scan the dropin, link folder and legacy configuration file in every Equinox launching. You can disable the capability by marking it not be early start.
org.eclipse.equinox.p2.reconciler.dropins,1.0.100.v20091010,plugins/org.eclipse.equinox.p2.reconciler.dropins_1.0.100.v20091010.jar,4,false

If finding some new bundles in dorpin folder, the reconciler would add the new bundles into a local metadata repository that is stored as OSGi data of Equinox. Then synchronize the bundles into the current p2 profile, then add the new bundles into bundles.info file.