Hello,
On 2023-12-05 01:47, chenpingyuan--- via Devel wrote:
By saying " threads that are blocked waiting in an endpoint or
notification queue will remain in the queue and can still recieve
messages and signals.", does it mean that those threads blocked waiting
in an endpoint or notification queue will remain in the READY QUEUE?
Or maybe the manual was not accurate?
The manual is accurate, but it does not document the scheduling queues
in detail, like the ready queue (called "scheduling queue" in the
manual)
or the release queue (queue of threads waiting for more budget, not to
be confused with "replenishment queue", which each scheduling context
has and doesn't queue threads, but budget refills).
It does document the end point queue though in chapter 4.2.
Notifications
also have a queue which isn't clearly described, but it is very similar
to end points, as mentioned in 6.1.7. Every end point and notification
object have a queue where threads that block on them will be queued on.
All threads can only be in one queue at the time, either one of the
scheduling ones, or an end point or notification queue. Because of this
it is not possible to wait for multiple end points or notifications at
the same time. The only exception is waiting for an end point and a
bound
notification at the same time, as the end point code does extra checking
for bound notifications.
For details like these you have to read the seL4 source code, though
higher levels things can be hard to extract from the source.
Maybe you confused me with "ready queue", as that is the name in the
source code for the scheduling queue for active threads, but perhaps
you meant the EP/NF queues instead. If that's the case, to perhaps
answer your actual previous question:
Yes, threads which are blocked waiting for notification/endpoint
without schedule context will remain in the object's queue.
This is possible because when they unblock, they will get a scheduling
context, and this is also the only way to unblock them, so they don't
need to be queued anywhere else. For end points the caller's SC will be
donated, for notifications the bound SC will be used.
However, I don't know what happens if a scheduling context disappears
because of a call to seL4_SchedContext_Unbind() and there is no SC bound
to the NF (any more). I would the expect the behaviour to be the same as
when the thread gets suspended, however, seL4_TCB_Suspend() will call
cancelIPC(), but that doesn't seem to happen for
seL4_SchedContext_Unbind().
Greetings,
Indan
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