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