[erlang-questions] asynchronous driver, ready_input

Dennis Novikov dennis.novikov@REDACTED
Thu Nov 20 17:53:02 CET 2008

Hi, all.

Does ready_input callback of asynchronous erlang driver have to be

typedef struct {
   ErlDrvPort          port;
   int                 fd;
   char                *rb; // result buffer
} drv_data;

I am allocating memory buffer in start callback like this

  static ErlDrvData drv_start(ErlDrvPort port, char *buff)
     drv_data* d = (drv_data*)driver_alloc(sizeof(drv_data);
     d->port = port;
     d->rb = (char*) driver_alloc(BUF_SZ);

     set_port_control_flags(port, PORT_CONTROL_FLAG_BINARY);

     driver_select(d->port, (ErlDrvEvent)d->fd, DO_READ, 1);

And in ready_input callback:

  static void data_ready(ErlDrvData handle, ErlDrvEvent evt)
      drv_data *d = (drv_data*)handle;
      char *rbuf = d->rb;

      int len = get_len();

      put_some_data_into(rbuf);          //
                                         //  Is this safe?
      driver_output(d->port, rbuf, len); //

The code above is simplified. Be it real I would use
driver_output_binary(). If I understand correctly, that happens
behind the scene in driver_output() call, so I should be safe.
Am I?


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