read serial interfaces inside of a thread

Hello,
I want to read/write 10 serial interfaces inside of a thread (one after
another in the thread-function, but in the thread). It seems to work,
but sometimes my program hangs. I wonder if the read/write-thread might
the cause.

Does the libc is thread-safe for reading/writing the serial lines (or
generally reading/writing device files)?


Libs which are used:
libstdc++-3-libc6.2-2-2.10.0.so
libc.so.6
libpthread.so.0


Thanks in advance,
Juergen