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4 :     <title>Auto-refresh overview</title>
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9 :     <h1>Auto-refresh overview</h1>
10 :     <font size="-1">Last modified: February 20, 2004</font>
11 :     <p>
12 :     In Eclipse 3.0 an auto-refresh facility was added to the
13 :     org.eclipse.core.resources plugin. This feature, when enabled, searches
14 :     the file system for changes that have been made externally, and then
15 :     automatically refreshes the workspace when new changes are discovered. This
16 :     document briefly describes the architecture of auto-refresh.
17 :     </p>
18 :     <p>
19 :     Plug-ins provide change notification to the workspace by hooking into the
20 :     new <tt>refreshProviders</tt> extension point. Extensions to this extension
21 :     point implement subclasses of the following abstract class:
22 :     <pre>
23 :     public abstract class RefreshProvider {
24 :     public abstract IRefreshMonitor installMonitor(IResource resource, IRefreshResult result);
25 :     }
26 :     </pre>
27 :     </p>
28 :     <p>
29 :     When a new project or linked resource is added to the workspace, each installed
30 :     refresh provider is asked to install a refresh monitor on that location. If for any
31 :     reason a refresh provider is not able to monitor a given location, it can opt not to
32 :     return a monitor. If no installed refresh providers are willing to monitor the location
33 :     (or if no refresh providers are installed), a default refresh provider is implemented
34 :     by the platform. This default refresh provider uses a naive Java-based polling
35 :     loop that manually checks for changes in the location at a specified interval
36 :     (by default, 30 seconds).
37 :     </p>
38 :     <p>
39 :     Once installed, a monitor is responsible for notifying the workspace when external
40 :     changes are made to that file system location by invoking methods on the provided
41 :     callback interface (<tt>IRefreshResult</tt>). The results are collected by the
42 :     workspace, and the workspace will synchronize the changed resources in
43 :     a periodic background job. Note that this hand-off is entirely asynchronous.
44 :     The monitor is responsible for identifying out of sync resources, and in a separate
45 :     thread the workspace will process those changes and reconcile them with
46 :     the workspace tree.
47 :     </p>
48 :     <p>
49 :     The Eclipse SDK includes refresh provider implementations for both Win32 and Linux
50 :     platforms. On all other platforms, the default Java-based polling refresh provider
51 :     is used, unless another plug-in is installed that provides a more efficient
52 :     platform-specific implementation. On Windows, the refresh provider uses win32
53 :     API calls to install a native file system monitor (FindFirstChangeNotificationW
54 :     in windows.h). File system monitors in win32 are <b>deep</b>, i.e., they report
55 :     changes on an entire file sub-tree.
56 :     </p>
57 :     <p>
58 :     On Linux, the refresh provider use a standard Unix utility
59 :     called FAM (File Alteration Monitor), that is installed by default on most Linux
60 :     distributions. FAM runs a daemon that uses a native polling loop to detect changes in
61 :     the file system. Clients can install a monitor on individual directories, and they are
62 :     provided with a change event queue that they can process at will (either with a blocking
63 :     dequeue operation or by peaking at the queue in their own polling loop). FAM
64 :     monitors are <b>shallow</b>, i.e., you need to install separate monitors on
65 :     each folder of a sub-tree.
66 :     </p>
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