[lwip-devel] [task #6683] Document lwIPs thread safety requirements

[Simon Goldschmidt]

Follow-up Comment #8, task #6683 (project lwip):

>but sys_mbox_post can be a problem: OS-provided mailboxes may not be
interrupt-safe - they may only be intended to be task-safe.

>because posting to a mailbox can cause a task switch

Good point... If posting to a mailbox should always succeed, other tasks
might have to run until there is free space in the mailbox. But eCos is
designed to have DSRs, while e.g. µC/OS is not. In µC/OS (as in other
OSes), there is a function like mbox_trypost().

I think whether mbox posting can be used from interrupt context or not is up
to the user to decide. After all, the 'user' is still a developer who should
know it's system...

Involving mem_free() (and thus, waiting for a semaphore) waits (and
context-switches) on _every_ OS, so at least TX-interrupt must not call
pbuf_free() with the current code...

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