| Property | Description |
| qosChannelMaxSize | Sets the maximum number of events which will be queued (buffered) by each EventChannel. The default value for all platforms, except for VxWorks, is 10240 events.The default value for VxWorks is 100 (due to constraints related to this specific platform). |
| qosProxyMaxSize | Sets the maximum number of events which will be queued by each ProxyPushSupplier. The default value, except for VxWorks, is 1024 events.The default value for VxWorks is 100 (due to constraints related to this specific platform). |
| qosChannelPushMode | Sets the EventChannel push mode to BLOCK or REJECT.The push mode determines whether push callers will be blocked (BLOCK) or their events rejected (REJECT) when the channel's queue is full. BLOCK is the default.(See Blocking versus Rejecting Events below.) |
| qosProxyPushMode | Sets the ProxyPushSupplier's push mode to BLOCK or REJECT.The push mode determines whether the event channel will be blocked from pushing events (BLOCK) or the events rejected (REJECT) when the proxy's queue is full. BLOCK is the default.(See Blocking versus Rejecting Events below.) |
| qosProxyStackSize | Sets the proxy queue thread's stack size in bytes. The default value of zero (0) sets the stack size to the platform's default stack size. |
# Example 1
Setting the Configuration Structure Fields’ Default Values at Initialisation
```txt
EORB_EventService_Config config =
{
EORB_EventService_DEFAULT_CHANNEL_MAX_SIZE,
EORB_EventService_DEFAULT_PROXY_MAX_SIZE,
EORB_EventService_BLOCK,
EORB_EventService_BLOCK,
0
};
```
# Example 2
Setting the Configuration Structure Fields’ Other Values at Initialisation
```c
EORB_EventService_Config config =
{
1000, /* qosChannelMaxSize */
100, /* qosProxyMaxSize */
EORB_EventService_REJECT, /* qosChannelPushMode */
EORB_EventService_BLOCK, /* qosProxyPushMode */
4096 /* qosProxyStackSize */
};
```
# Example 3
Setting the Configuration Structure Field values directly
```txt
EORB_EventService_Config config;
config.qosChannelMaxSize = 1000;
config.qosProxyMaxSize = 100;
config.qosChannelPushMode = EventService.REJECT;
config.qosProxyPushMode = EventService.BLOCK;
config.qosProxyStackSize = 4096;
```
# 2.1.1.1 Blocking versus Rejecting Events
The block and reject push modes enable users to alter the behaviour of the Event Service to best suit their particular needs regarding how the transmission of events are treated when the event channel and proxy queues are full. Generally, BLOCK ensures that all events are received (subject to the limitations of Best Effort Quality of Service1) at the expense of the transmission rate being limited to the slowest consumer, whereas REJECT ensures the fastest possible speed at the expense of losing events sent to slow consumers.
# 2.1.1.1.1 Event Channel
If the event channel’s queue is full and its push mode is set to block, then the clients which are pushing events onto the channel will be blocked (i.e. they must wait until the queue has space to accept events). The block mode ensures that no events are lost.
If the event channel’s queue is full and its push mode is set to reject, then clients can continue to push events onto the channel. However, events will be rejected (i.e. lost) and a IMP\_LIMIT exception will be returned to the client for each rejected event. The result is that events will be lost, plus there is the added overhead of returning the exception.
# 2.1.1.1.2 Proxy Push Supplier
If the ProxyPushSupplier’s queue is full and its push mode is set to block, then the event channel will be blocked from sending events to any proxy. The block mode ensures that no events are lost (subject to Best Effort), however the rate that events can be sent to consumers is limited to the rate of the slowest consumer.
If a ProxyPushSupplier’s queue is full and its push mode is set to reject, then the event channel will continue to push events to all consumer clients connected to the channel, however events will be rejected (i.e. lost) by the ProxyPushSupplier whose queue is full. Consumers which can accept events more quickly are allowed to continue to receive events, but the (slower) consumer will lose events.
# 2.1.2 The EORB\_EventService\_init() Method
The Event Service’s EORB\_EventService\_init() method initialises an Event Service instance. The method takes two parameters:
• a reference to the orb object the service is to be run on
• a reference to the poa which the service will run in
• the configuration structure (described under Configuration Structure on page 13)
The method returns the instance’s reference. This reference can be used directly, or be stored or pushed for use by other methods, modules, etc.
# Example 4
Using the EORB\_EventService\_init() Method
The following code extract creates an Event Service (channel) instance using the EORB\_EventService\_init() method. The EORB\_EventService\_init() method takes an ORB object (created using CORBA\_ORB\_init()), a POA object or NULL and a configuration structure instance (see Example 2 on page 15). If the POA is NULL then the service will resolve the RootPOA from the ORB.
```c
CosEventChannelAdmin_EventChannel channel;
channel = EORB_EventService_init (orb, poa, &config, &env);
```
# 2.1.3 Simple Example
The source code for a simple example showing how the Event Service can be run from the command line is provided under lweventc Source Code on page 18.
Complete source code examples which illustrate the use of the Event Service are also provided in examples/c/services/event.
# 2.2 Running from the Command Line
The Event Service can run from the command line using the lweventc example executable with zero or more of the options listed in Table 2. These options are the command line equivalent of the embedded service’s configurable properties.
```txt
% lweventc [options]
```
The complete source code for lweventc is shown following Table 2.
i Blocking versus Rejecting Events, below, should be read before using the -EventServiceChannelPushMode or -EventServiceChannelPushMode options.
Table 2 Command Line Options
| Option | Description |
| -EventServiceChannelMaxSize | Sets the maximum number of events, , which will be queued (buffered) by the EventChannel.The default value for all platforms, except for VxWorks, is 10000 events.⚠ The default value for VxWorks is 100 (due to constraints related to this specific platform). |
| -EventServiceChannelPushModeREJECT> | Sets the EventChannel push mode. The push mode determines whether push callers will be blocked (BLOCK) or their events rejected (REJECT) when the channel's queue is full. BLOCK is the default.The default is BLOCK.(See Blocking versus Rejecting Events on page 15.) |
| -EventServiceProxyMaxSize | Sets the maximum number of events, , which will be queued by the ProxyPushSupplier. The default value for all platforms, except for VxWorks, is 1024 events.⚠ The default value for VxWorks is 100 (due to constraints related to this specific platform). |
| -EventServiceChannelPushModeREJECT> | Sets the ProxyPushSupplier's push mode. The push mode determines whether the event channel will be blocked from pushing events (BLOCK) or the events rejected (REJECT) when the proxy's queue is full.The default is BLOCK.(See Blocking versus Rejecting Events on page 15.) |
Table 2 Command Line Options