When an event is posted, it is distributed to the subscribers
by the EVM daemon. Before you can post the event, you must create
a posting connection to the Event Manager daemon.
Example 4-4 “Posting Events” shows how
to create the connection, post the event, and disconnect the connection.
Example 4-4 “Posting Events” introduces
the following functions:
EvmConnCreate — Establishes
a connection between an application program and EVM, and defines
how I/O activity is to be handled. A separate connection must be
established for each type of connection: posting, listening (subscribing),
or availing service. For more information about this function, see EvmConnection(5) and EvmConnCreate(3).
EvmEventPost — Posts
an event to EVM. For more information about this function, see EvmEventPost(3).
EvmConnDestroy — Destroys
a specified connection. For more information about this function,
see EvmConnDestroy(3).
You can use the simpler EvmConnCreatePoster() macro in place of EvmConnCreate() to create a posting connection. This macro requires fewer
arguments than EvmConnCreate(). Although it offers fewer connection options, it is
suitable for use by most applications that need to post events to
the local system.
If your program uses transient EVM connections, you can omit
calls to EvmConnCreate() or EvmConnDestroy() and pass NULL as the connection argument to EvmEventPost(). Connections use significant processing time to establish,
so you must use only transient connections if they are appropriate
for your program. For more information about connections, see “Choosing a Connection
Policy” and
EvmEventPost(3).
You can create, post, and destroy an event in a single call
using the EvmEventPostVa() function. For more information about this function, see EvmEventPost(3).
Example 4-4 Posting Events
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#include <stdio.h>#include <evm/evm.h>int main(){ EvmEvent_t event; EvmStatus_t status;EvmConnection_t conn; EvmItemValue_t itemval_name; /* You can create a connection to the EVM daemon using EvmConnCreate() function. The connection remains in place until your program exits, or until you explicitly destroy it with EvmConnDestroy(). The first two arguments to EvmConnCreate() function specify that the connection will be used for posting events. This function waits for the daemon to acknowledge acceptance of the event before returning, so that you can take action if the attempt fails. (See EvmConnCreate (3) for other response options.) The NULL value for the third argument indicates that you are making a connection to the EVM daemon running on the local system. The fourth and fifth values are used for other response types, and should always be NULL for wait-mode responses. The final argument receives the handle to the connection b you must supply the returned value in all future calls being made on this connection.*/ status = EvmConnCreate(EvmCONNECTION_POST, EvmRESPONSE_WAIT,NULL,NULL,NULL,&conn); if (status != EvmERROR_NONE) { fprintf(stderr,"Failed to create EVM posting connection\n"); exit(1); } /* Create an event and post it. */ itemval_name.NAME="sys.unix.evm"; EvmEventCreateVa(&event, EvmITEM_NAME, itemval_name,EvmITEM_NONE); status = EvmEventPost(conn,event); if (status != EvmERROR_NONE) { fprintf(stderr,"Failed to post event\n"); exit(1); } /* Clean up by destroying the event and the connection. If you expect posting events periodically, it may be better not to destroy the connection, but to reuse it for all future events. This will save you the overhead of re-establishing the connection each time you have something to post.*/ EvmEventDestroy(event); EvmConnDestroy(conn);} |
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