Specify the number of threads to be executed concurrently in the entire J2EE server for processing callback of the timeout method. This is called the maximum number of callback threads.

When multiple EJB timers timeout concurrently, depending upon the maximum number of callback threads of the timeout method, the operation will be as follows:

• When the maximum number of callback threads is 1 (default)
  Callback is executed sequentially. As a result, callback may start even later than the time set in the EJB timer.
  
• When the maximum number of callback threads is 2 or more
  Only the specified number of callback processes are executed concurrently. If you increase the maximum thread count, the resource consumption will increase by an equal amount. Therefore, specify an appropriate value for the number of threads to be executed concurrently.
  

The following figure shows the relationship between the settings for the maximum number of callback threads and callback processing:

Figure 2-25 Relationship between the settings for the maximum number of callback threads and callback processing

In this figure, the settings are specified so that EJB timer 2 will be timed out one minute after the timeout of the EJB timer 1 occurs. When the maximum number of callback threads is set to 1, the callback processing of EJB timer 2 will start after the callback processing of the EJB timer 1 finishes. When the maximum number of callback threads is specified as 2, two callback processes can be executed concurrently, therefore, the callback processing of EJB timer 2 is started one minute after the EJB timer 1, as per the settings.

Note

Even if there is a surplus in the number of callback threads, but a shortage of instances of Enterprise Beans, the callback processing is executed after awaiting release of the instances. Therefore, specify the Enterprise Bean instance pool after considering the number of instances to be called back.

In the case of a failure in calling back the timeout method, retry callback.

Callback may fail in the following cases:

• When an unsearched exception (java.lang.RuntimeException, java.lang.Error and their subclasses) is thrown during callback due to a timeout
• When the timeout method is either the Required attribute or the RequiresNew attribute of CMT and the transaction rolls back

Set the following settings for retrying callback:

Number of retry

Specify the number of retries. When you specify 0, retry is not performed. If the count of executing retries reaches the specified retry number, retry is not performed at a timeout.

Interval of executing retry

Specify the time period from failure of a callback until the retry callback.