[lwip-devel] [bug #27377] "op_completed" semaphore mechanism crash error

[hanhui]

Follow-up Comment #1, bug #27377 (project lwip):

another BUG found: user thread and tcpip thread synchronization mechanism.

for example: here are 3 thread: recv_thread() send_thread() tcpip_thread().
recv_thread() has the highest priority. tcpip_thread() has the middle
priority, send_thread() has the lowest priority of all.

one time, send_thread call tcpip_apimsg() to add a do_send() job to
tcpip_thread, after mbox post, tcpip_thread run immediately. now send_thread
do not wait for op_completed semaphore. at this time send_thread does not wait
for op_completed semaphore, then tcpip_thread execute do_send() job... at this
time recv_thread() wake up, preempt all other thread, and is call
tcpip_apimsg() to add a do_recv() job to tcpip_thread, mbox post do not cause
a preempt, and then recv_thread wait for op_completed semaphore. then
tcpip_thread resume execute do_send()... when do_send() finish, it will signal
op_completed semaphore. NOW! not send_thread get is signal, but recv_thread.


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