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The ptree_register_handler() function registers an event handler for a PICL event. The argument ename specifies the name of the PICL event for which to register the handler. The argument evt_handler specifies the event handler function.
The argument cookie is a pointer to caller-specific data to be passed as an argument to the event handler when it is invoked.
The event handler function must be defined as
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void evt_handler(const char *ename, const void *earg, \
size_t size, void *cookie)
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where, ename, earg, size, and cookie are the arguments passed to the event handler when it is invoked. The argument ename is the PICL event name for which the handler is invoked. The arguments earg and size gives the pointer to the event argument buffer and its size, respectively. The argument cookie is the pointer to the caller specific
data registered with the handler. The arguments ename and earg point to buffers that are transient and shall not be modified by the event handler or reused after the event handler finishes execution.
The PICL framework invokes the event handlers in the order in which they were registered when dispatching an event. If the event handler execution order is required to be the same as the plug-in dependency order, then a plug-in should register its handlers from its init function. The handlers that
do not have any ordering dependencies on other plug-in handlers can be registered at any time.
The registered handler may be called at any time after this function is called.
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