For a plug-in created before Apama release 5.1 to work with Apama 5.1, you must re-compile it. Beginning with release 4.2, the interface is more accurate with respect to the use of const, so minor code changes may be required.

Plug-ins created before Apama 4.2, and new plug-ins that do not mark themselves as thread-safe, run in a single operating system thread at a time. The correlator assumes that such plug-ins are not thread-safe. For each call to such a plug-in, the correlator acquires a mutex to ensure that multiple correlator contexts cannot use the plug-in at the same time.

When multiple contexts need to concurrently use a plug-in you must ensure that the plug-in is thread safe. A plug-in can export a function that returns the capabilities of the plug-in. See the AP_PluginCommon.h header file for the definition of AP_PLUGIN_GET_CAPABILITIES_FUNCTION_NAME. The correlator calls this function before it calls the plug-in’s init() function. The return value is a bit-wise OR of capabilities, as defined in the AP_PluginCommon.h header file. If the return value indicates that the plug-in is thread-safe, multiple contexts can make concurrent calls to the plug-in. When multiple contexts need to concurrently use a plug-in, you must ensure that the plug-in is thread-safe.

A plug-in can use a context’s ID to send events to a particular context. Use the AP_Context.getContextId() method to obtain the context ID. The correlator passes an AP_Context object to each plug-in. This object has a getCorrelator() method, which returns an interface that defines a sendEventTo() method.

The sendEventTo() method takes three arguments: