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[lwip-users] Question about sys_arch.c *_free() vs. *_~set_invalid()

From: Grant Edwards
Subject: [lwip-users] Question about sys_arch.c *_free() vs. *_~set_invalid()
Date: Thu, 11 Nov 2021 21:00:40 -0000 (UTC)
User-agent: slrn/1.0.3 (Linux)

[Sorry for all of the porting questions, but the sys_arch.c file I'm
working with just doesn't seem to make sense.]

I don't understand how *_free() and *_set_invalid() are supposed to

In the code I've inherited, when *_free() is called, my sys_arch.c
code places the referenced kernel object (semaphore or mailbox) back
into the free pool and it becomes available to be reallocated and
placed into use.

The lwIP documentation states:

   void sys_sem_set_invalid(sys_sem_t *sem)

   Invalidate a semaphore so that sys_sem_valid() returns 0.
   ATTENTION: This does NOT mean that the semaphore shall be
   deallocated: sys_sem_free() is always called before calling this

Apparently the sequence is


If invalid() is called for a particular semaphore _after_ that
semaphore has been free()ed, that semaphore may have already been
reallocated and might be in use by a different thread, socket,
whatever. Is the semaphore not supposed to be availble for
reallocation after being free()ed?

Are signal/wait calls on a mutex allowed between the free() call and
the set_invalid() call?


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