select_attach()

Attach a file descriptor to a dispatch handle

Synopsis:

#include <sys/iofunc.h>
#include <sys/dispatch.h>

int select_attach 
        ( void *dpp,
          select_attr_t *attr,
          int fd,
          unsigned flags,
          int (*func)( select_context_t *ctp,
                      int fd,
                      unsigned flags,
                      void *handle ),
          void *handle );

Arguments:

dpp

The dispatch handle, as returned by dispatch_create(), that you want to attach to a file descriptor.

attr

A pointer to a select_attr_t structure. This structure is defined as:

typedef struct _select_attr {
   unsigned                 flags;
} select_attr_t;
  

Currently, no attribute flags are defined.

fd

The file descriptor that you want to attach to the dispatch handle.

flags

Flags that specify the events that you're interested in. For more information, see “Flags,” below.

func

The function that you want to call when the file descriptor unblocks. For more information, see “Function,” below.

handle

A pointer to arbitrary data that you want to pass to func.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The function select_attach() attaches the file descriptor fd to the dispatch handle dpp and selects flags events. When fd “unblocks”, func is called with handle.

Flags

The available flags are defined in <sys/dispatch.h>. The following flags use ionotify() mechanisms (see ionotify() for further details):

SELECT_FLAG_EXCEPT

Out-of-band data is available. The definition of out-of-band data depends on the resource manager.

SELECT_FLAG_READ

There's input data available. The amount of data available defaults to 1. For a character device such as a serial port, this is a character. For a POSIX message queue, it's a message. Each resource manager selects an appropriate object.

SELECT_FLAG_WRITE

There's room in the output buffer for more data. The amount of room available needed to satisfy this condition depends on the resource manager. Some resource managers may default to an empty output buffer, while others may choose some percentage of the empty buffer.

These flags are specific to dispatch:

SELECT_FLAG_REARM

Rearm the fd after an event is dispatched.

SELECT_FLAG_SRVEXCEPT

Register a function that's called whenever a server, to which this client is connected, dies. (This flag uses the ChannelCreate() function's _NTO_CHF_COID_DISCONNECT flag. In this case, fd is ignored.)

Function

The argument func is the user-supplied function that's called when one of the registered events occurs on fd. This function should return 0 (zero); other values are reserved. The function is passed the following arguments:

ctp

Context pointer.

fd

The fd on which the event occurred.

flags

The type of event that occurred. The possible flags are:

• SELECT_FLAG_EXCEPT
• SELECT_FLAG_READ
• SELECT_FLAG_WRITE

For descriptions of the flags passed to func, see “Flags,” above.

handle

The handle passed to select_attach().

Returns:

Zero on success, or -1 if an error occurred (errno is set).

Errors:

EINVAL

Invalid argument.

ENOMEM

Insufficient memory was available.

Examples:

For an example with select_attach(), see dispatch_create(). For other examples using the dispatch interface, see message_attach(), resmgr_attach(), and thread_pool_create().

Classification:

QNX Neutrino

See also:

select_detach(), select_query()