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I
InterruptUnblock(), InterruptUnblock_r()
Calls to the kernel to post a semaphore associated with an interrupt handler

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        Support pathconf() requests
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        Default handler for _IO_READ messages
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        Verify a client's read access to a resource
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        Verify the attributes being used to read a link
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        Do permission checks for a _IO_CONNECT_RENAME message
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        Do permission checks for the _IO_SPACE message
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        Populate a stat structure
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        Default handler for _IO_STAT messages
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        Indicate if synchronization is needed
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        Default handler for _IO_SYNC messages
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        Verify permissions to sync
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        Update time stamps
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        Unblock OCBs
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        Default unblock handler
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        Verify that an entry can be unlinked
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        Default handler for the unlock_ocb callout
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        Update time stamps
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        Default handler for _IO_UTIME messages
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        Default handler for _IO_WRITE messages
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        Verify a client's write access to a resource
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        Arm a resource manager
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        Determine if a number is finite
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        Determine whether one floating-point number is greater than another
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        Determine whether one floating-point number is greater than or equal to another
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        Test for infinity
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InterruptUnblock(), InterruptUnblock_r()

QNX SDP8.0C Library ReferenceAPIDeveloper

Calls to the kernel to post a semaphore associated with an interrupt handler

Synopsis:

#include <sys/neutrino.h>

int InterruptUnblock(int id);

Arguments:

interrupt handler id: The id of the interrupt handler used in a call to InterruptUnblock().

Library:

libc

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

Description:

InterruptUnblock() allows an Interrupt Service Thread (IST) to be made ready for a reason other than receiving an interrupt. For example, InterruptUnblock() may be used as a mechanism that ensures an IST can detach itself.

A process that uses an IST may require a thread to be detached from its interrupt. For example, if:

The IST must exit cleanly while the process is still running.
The IST must attach itself to a different interrupt source.

A typical implementation consists of the following steps:

Set a global flag (so that the IST can distinguish between a hardware interrupt and an event from InterruptUnblock()).
Memory barrier.
Invoke the InterruptUnblock() kernel call.

Note:

You must implement a mechanism to distinguish between a hardware interrupt and a thread unblocking the IST. Setting a global flag is given as an example of one method for implementing such a mechanism.

The IST is expected to check the flag every time the kernel call (to wait for an interrupt) returns. It can then detach itself from the interrupt.

Note:

The IST cannot distinguish between a real interrupt arriving, and the result of the kernel call to post the handler. It is even possible for the two events to occur before the IST has a chance to run in its user persona, following a call to wait on an interrupt.

Returns:

The only difference between these functions is the way they indicate errors:

InterruptUnblock(): If an error occurs, -1 is returned and errno is set. Any other value returned indicates success.
InterruptUnblock_r(): EOK is returned on success. This function does NOT set errno. If an error occurs, any value in the Errors section may be returned.

Classification:


Safety:
Cancellation point	No
Signal handler	Yes
Thread	Yes

Page updated: August 11, 2025