Erlang and OTP in Action.pdf - Synrc

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NULL, /* F_PTR init, N/A */
drv_start, /* L_PTR start, called when port is opened */
drv_stop, /* F_PTR stop, called when port is closed */
NULL, /* F_PTR output, called when erlang has sent */
NULL,
/* F_PTR ready_input, called when input descriptor ready
*/
NULL,
/* F_PTR ready_output, called when output descriptor
ready */
"lzjb_compress", /* char *driver_name, the argument to open_port */
NULL, /* F_PTR finish, called when unloaded */
NULL, /* F_PTR handle */
NULL, /* F_PTR control, port_command callback */
NULL, /* F_PTR timeout, reserved */
drv_outputv, /* F_PTR outputv, reserved */
NULL, /* ready_async */
NULL, /* flush */
NULL, /* call */
NULL, /* event */
ERL_DRV_EXTENDED_MARKER, /* extended marker */ /* enable the
rest */
ERL_DRV_EXTENDED_MAJOR_VERSION, /* major version */
ERL_DRV_EXTENDED_MINOR_VERSION, /* minor version */
ERL_DRV_FLAG_USE_PORT_LOCKING, /* driver_flags */ /* better
locking */
NULL, /* handle2 */ /* set by the VM
*/
NULL /* process_exit */
};
This is almost the same struct that we declared in our earlier example. There are two main
differences. The first is that we changed a couple of names to be a little more clear and
consistent. The second is that we are going to use the outputv callback instead of the
process callback. This allows us to access the data we need to parse directly and in an
asynchrounous fasion. Other than that things are pretty similar.
The last thing we do in setting up our driver is just declare the entry point to Erlang and
return this struct to the VM.
DRIVER_INIT(lzjb_compress)
{
return &driver_entry;
}
As you can see this is exactly the same as the function we used in our last example. Of
course, the name that we pass into the DRIVER_INIT macro changes but that’s it. You should
remember that this name must match the name specified in the name section of the
description struct.
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