PPARALLEL_TRY_ALLOCATE_ROUTINE callback function (parallel.h)

Article
02/22/2024

The PPARALLEL_TRY_ALLOCATE_ROUTINE-typed (ISR) callback routine attempts to allocate a parallel port at IRQL = DIRQL. The system-supplied function driver for parallel ports supplies this routine.

Syntax

PPARALLEL_TRY_ALLOCATE_ROUTINE PparallelTryAllocateRoutine;

BOOLEAN PparallelTryAllocateRoutine(
  [in] PVOID TryAllocateContext
)
{...}

Parameters

[in] TryAllocateContext

Pointer to the device extension of a functional device object that represents a parallel port.

Return value

Return code	Description
TRUE	The parallel port was allocated.
FALSE	The parallel port was not allocated.

Remarks

A kernel-mode driver connects an interrupt service routine by using an IOCTL_INTERNAL_PARALLEL_CONNECT_INTERRUPT, which returns a PARALLEL_INTERRUPT_INFORMATION structure. This structure includes the TryAllocatePortAtInterruptLevel member, which is a pointer to the system-supplied PPARALLEL_TRY_ALLOCATE_ROUTINE (ISR) callback.

The PPARALLEL_TRY_ALLOCATE_ROUTINE (ISR) callback is nonblocking, does not queue an allocate request, and returns immediately.

A driver uses the PPARALLEL_TRY_ALLOCATE_ROUTINE (ISR) callback in conjunction with a driver-supplied ISR. If the driver does not have a parallel port allocated when the driver's ISR is called, the driver can use this callback.

For more information about allocating a parallel port in an ISR, see Connecting an Interrupt Service Routine to a ParallelPort.

Note The PPARALLEL_TRY_ALLOCATE_ROUTINE (ISR) callback is untested. Microsoft does not recommend using a client-supplied interrupt routine. The use of interrupts might cause system instability. By default, the IOCTL_INTERNAL_PARALLEL_CONNECT_INTERRUPT request is disabled.

Requirements

Requirement	Value
Target Platform	Desktop
Header	parallel.h (include Parallel.h)
IRQL	DIRQL