So L4Re is POSIX compliant?On Fri, Oct 10, 2014 at 12:16 PM, Björn Döbel <doebel@os.inf.tu-dresden.de> wrote:
Am 10.10.2014 um 18:00 schrieb teclis High Elf:
I have two threads running in the same server. On thread handles
incoming ipc messages from the clients in different address spaces and
the other thread does the work. The thread handling the incoming ipc
needs to pass an integer value to the worker thread. Could I synchronize
them using
int l4util_cmpxchg32
<https://os.inf.tu-dresden.de/L4Re/doc/group__l4util__atomic.html#gacb4a5e47fea67cc4c61b488fc374df62>
(volatile l4_uint32_t
<https://os.inf.tu-dresden.de/L4Re/doc/group__l4__basic__types.html#gac1d09f3e382e711b776931f10e6e1e5a>
*dest, l4_uint32_t
<https://os.inf.tu-dresden.de/L4Re/doc/group__l4__basic__types.html#gac1d09f3e382e711b776931f10e6e1e5a>
cmp_val, l4_uint32_t
<https://os.inf.tu-dresden.de/L4Re/doc/group__l4__basic__types.html#gac1d09f3e382e711b776931f10e6e1e5a>
new_val)
the worker thread could then check the value of dest to get the integer.
Would the worker thread need to use an atomic read function when it
reads the value of dest and if so which function would the worker thread
use for the atomic read?
In your scenario, I would think of it like this:
int data = -1; // global variable, set to invalid value
server_thread()
{
int val = receive_message();
data = some_processing(val);
}
worker_thread()
{
while (data == -1) // spin until data is valid
;
/* Use data here */
}
I don't see the need for an atomic cmpxchg() in your specific case. Actually I would however suggest you use a pthread_mutex or a pthread_cond_var to synchronize your threads (or even IPC between the two...).
Bjoern
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