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| Concurrency and the workspace |
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| <h3>Concurrency and the workspace</h3> |
| |
| <p>We've already seen that workspace code must be aware of concurrency even if it is not using the |
| concurrency framework. Batching of workspace changes and use of scheduling rules helps in sharing |
| the workspace with other plug-ins (and their threads) that are modifying the workspace. Once your plug-in |
| is using batching and rules (see <a href="resAdv_batching.htm">Batching resource changes</a>), it is |
| easy to perform the same work using the platform concurrency mechanisms. |
| </p> |
| |
| <h4>Workspace jobs</h4> |
| <p>A <b><a href="../reference/api/org/eclipse/core/runtime/jobs/Job.html">Job</a></b> is a basic unit of |
| asynchronous work running concurrently with other jobs. The resources plug-in defines |
| <b><a href="../reference/api/org/eclipse/core/resources/WorkspaceJob.html">WorkspaceJob</a></b> |
| as a convenient mechanism for defining asynchronous resource modifications. Code that would |
| normally be batched in an <b><a href="../reference/api/org/eclipse/core/resources/IWorkspaceRunnable.html">IWorkspaceRunnable</a></b> |
| is instead put in the <b>runInWorkspace</b> method of a workspace job subtype. Instead of running the code using |
| <b><a href="../reference/api/org/eclipse/core/resources/IWorkspace.html">IWorkspace</a></b> protocol, |
| the job is scheduled just like any other job. The appropriate scheduling rules must be added on the job before |
| it is scheduled. |
| </p> |
| <p>Let's look at an example workspace runnable and what we should do to make it a job: |
| </p> |
| <pre>IWorkspaceRunnable myRunnable = |
| new IWorkspaceRunnable() { |
| public void run(IProgressMonitor monitor) throws CoreException { |
| //do the actual work in here |
| doSomeWork(); |
| ... |
| } |
| } |
| </pre> |
| <p>The work is moved to the appropriate method of our |
| <b><a href="../reference/api/org/eclipse/core/resources/WorkspaceJob.html">WorkspaceJob</a></b> |
| subtype. |
| </p> |
| <pre>class MyWorkspaceJob extends WorkspaceJob { |
| public MyWorkspaceJob() { |
| super("My Workspace Job"); |
| } |
| public IStatus runInWorkspace(IProgressMonitor monitor) { |
| //do the actual work in here |
| doSomeWork(); |
| return Status.OK_STATUS; |
| } |
| } |
| </pre> |
| <p>Our runnable had to be invoked specifically: |
| </p> |
| <pre>IWorkspace workspace = ResourcesPlugin.getWorkspace(); |
| workspace.run(myRunnable, myProject, IWorkspace.AVOID_UPDATE, null); |
| </pre> |
| <p>Our job is scheduled like any other job. The platform job manager will run it according to its |
| priority, other jobs in the queue, and the scheduling rules. Note that we must attach the |
| scheduling rule to the job in order to prevent simultaneous modification of <tt>myProject</tt>. |
| </p> |
| <pre>MyWorkspaceJob job = new MyWorkspaceJob(); |
| <b>job.setRule(myProject);</b> |
| job.schedule(); |
| </pre> |
| <p>Now that the operation has been structured as a job, all of the scheduling mechanisms (priority, delay, rescheduling) can |
| be used. Resource change events will be batched until the job is finished running. |
| </p> |
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