The POSIX path used mlock() as though it were a mutex. mlock only pins pages in
RAM - it provides no mutual exclusion at all, so the read-modify-write of the
cross-process instance counter was unsynchronized. Two instances launched at the
same moment could both come away with PPSSPP_ID == 1, at which point both pass
IsFirstInstance() and write ppsspp.ini over each other, and both compute the same
adhoc local IP. Take an advisory lock on the shm fd instead. (The Windows path was
already fine - it uses a named mutex.)
Also, next/total are uint8_t in a segment that outlives the processes using it, so
next climbs across runs and wraps. Landing on 0 is worse than it looks: it isn't a
valid instance id, IsFirstInstance() fails, and config saving is silently disabled
from then on. Skip past it on wrap.
Henrik Rydgård
85efe6ba7c