Lock and Unlock Operators Sample

Contents

Running LockUnlock.sbapp in StreamBase Studio
Running LockUnlock.sbapp in Terminal Windows
Importing This Sample into StreamBase Studio
Sample Location

This topic explains how we built the Lock and Unlock operators sample.

This sample uses paired Lock and Unlock operators to protect shared data against concurrent writes. The sample is intended only to demonstrate how to protect the data, and does not include other concurrent operations which might access the data. Other concurrent operations could derive from data on different streams sharing the query table, or they could be generated by tuples on the same stream, which would have to wait for the tuple being protected by the Lock clearing the Unlock (presumably there would be additional operators between the Lock and Unlock to process the data.)

This example uses the same key for both the key into the Query Table and the key on which to lock for exclusive access.

Running LockUnlock.sbapp in StreamBase Studio

In the Package Explorer, double-click to open the LockUnlock.sbapp application. Make sure the application is the currently active tab in the EventFlow Editor.
Click the Run button. This opens the SB Test/Debug perspective and starts the application.
In the Application Output view, select the ReturnProtectedData output stream. No output is displayed at this point, but the dequeuer is prepared to receive output. This view will eventually show the output of the application.
In the Manual Input view, select the WriteProtectedData input stream.
Enter 1 and xyz in the protectedDataKey and protectedDataValueInit fields, respectively.
Click Send Data, and observe this data appears in the Application Output view:
```
sharedDataLockKey=1, protectedDataLockKey=xyz
```
When done, press F9 or click the Stop Running Application button.

Running LockUnlock.sbapp in Terminal Windows

This section describes how to run the sample in UNIX terminal windows or Windows command prompt windows. On Windows, be sure to use the StreamBase Command Prompt from the Start menu as described in the Test/Debug Guide, not the default command prompt.

Open three terminal windows on UNIX, or three StreamBase Command Prompts on Windows. In each window, navigate to the directory where the sample is installed, or to your workspace copy of the sample, as described above.
In window 1, type:

sbd LockUnlock.sbapp

The window shows notice[StreamBaseServer] listening on port 10000.
In window 2, type:

sbc dequeue

There is no output immediately, but the dequeuer is primed to display subsequent output of the application.
In window 3, type:

sbc enqueue WriteProtectedData

The sbc command is now awaiting keyboard input. Type: 1,xyz.
In window 3, type: Ctrl+Z (Windows) or Ctrl+D (UNIX) to exit the sbc session.
Observe these lines in the dequeue window: ReturnProtectedData,1,xyz.
In window 3, type the following command to terminate the server and dequeuer:

sbadmin shutdown

Importing This Sample into StreamBase Studio

In StreamBase Studio, import this sample with the following steps:

From the top menu, click File → Load StreamBase Sample.
Select operator from the Data Constructs and Operators category.
Click OK.

StreamBase Studio creates a single project for the operator samples.

Sample Location

By default, the sample files are installed in:

On Windows: C:\Program Files\StreamBase Systems\StreamBase.n.m\sample\operator
On UNIX: /opt/streambase/sample/operator

When you load the sample into StreamBase Studio, Studio copies the sample project's files to your Studio workspace. StreamBase Systems recommends that you use the workspace copy of the sample, especially on UNIX, where you may not have write access to /opt/streambase. In the default installation, the path to this sample in your Studio workspace is:

UNIX:       
  ~/streambase-studio-n.m-workspace/sample_operator
Windows XP:
  C:\Documents and Settings\username\My Documents\StreamBase Studio n.m Workspace\
      sample_operator
Windows 7 and Windows Vista:
  C:\Users\username\Documents\StreamBase Studio n.m Workspace\
      sample_operator