ASYNC GETINQUECOUNT

Returns the number of characters in the receive queue.

Category

IOCTL_ASYNC (01h)

Function

ASYNC_GETINQUECOUNT (68h)

Parameter Packet Format

None. Packet pointer must be NULL.

Data Packet Format

┌──────────────────────────────────────────────────────┐
│Field                          Length     C Datatype  │
├──────────────────────────────────────────────────────┤
│Number of Characters Queued    WORD       USHORT      │
├──────────────────────────────────────────────────────┤
│Size of Receive Queue          WORD       USHORT      │
└──────────────────────────────────────────────────────┘

Related C Data Structure

The RXQUEUE data structure can be used by C programmers.

To include this data structure in your file, make sure INCL_DOSDEVIOCTL is defined before you include OS2.H.

Number of Characters Queued

Binary integer with the number of received characters in the device driver receive queue. This is a memory buffer between the memory pointed to by the READ request packet and the receive hardware for this COM device. The application cannot assume that there are no unsatisfied Read requests if there are characters in the device driver receive queue.

Note

The behavior of data movement between the Read request and the receive queue can change with each release of the physical device driver. Applications should not have a dependency on this information.

Size of Receive Queue

Binary integer with the size of the physical device driver receive queue. Applications should be independent of the receive queue being sized (fixed or not fixed). The information in this field allows the application to get the size of the receive queue. The current size of the receive queue is approximately 1KB, but is subject to change.

Using this information, the application should avoid device driver receive queue overruns by using an application-to-application block protocol with the system communicating with the application.

Returns

If the call is made with an invalid Parameter Packet value, a general failure error is reported, and valid information is not returned in the Data Packet.

Remarks

If a general failure error is not returned, the physical device driver returns the information.