PICC_Commit *PICC_try_output_action(PICC_Channel *chan, PICC_TryResult *res)
{
if (chan->global_rc == 1) {
*res = PICC_TRY_DISABLED;
return NULL;
}
PICC_Commit *commit = NULL;
PICC_CommitStatus ok = PICC_CANNOT_ACQUIRE;
do {
// search for a valid commitment
commit = PICC_fetch_input_commitment(chan);
if (commit == NULL) {
// if no valid or invalid commitment left, need to
// make an output commitment
*res = PICC_TRY_COMMIT;
return NULL;
}
// here, we have a candidate input commitment
// try to awake the commiting thread
do {
ok = PICC_process_can_awake(commit);
if (ok == PICC_CANNOT_ACQUIRE) {
sched_yield();
}
} while (ok == PICC_CANNOT_ACQUIRE);
// here we have either a valid commitment and an awoken thread,
// or an invalid commitment that we just removed (lazy deletion)
if (ok == PICC_VALID_COMMIT) {
// ok, everything's fine: a synchronization will occur
*res = PICC_TRY_ENABLED;
return commit;
}
} while (!(PICC_commitlist_is_empty(chan->incommits)));
PICC_CRASH(ERR_DEAD_CODE_REACHED);
return NULL;
}
/**
* The runtime support for output actions.
*
* @param pt the PiThread structure of the thread trying to output
* @param chan_ref the environment index of the output channel
* @param chans the acquired channels (cf. compilation of output try)
* @param nbchans the number of acquired channels
* @param try_result an output variable for the result of the try (ENABLED if output can be performed, DISABLED if not, and COMMIT if a commiment must be recorded).
* @return the matching input commitment, if any or NULL otherwise.
*/
PICC_Commit * PICC_try_output_action(PICC_PiThread *pt, int chan_ref, PICC_Channel* chans[], int nbchans, PICC_TryResult * try_result) {
PICC_Channel* out_chan = PICC_channel_of_channel_value(&(pt->env[chan_ref]));
// acquire the channel, if required
if (chan_array_add(out_chan, chans, &nbchans)) {
LOCK_CHANNEL(out_chan);
}
if(out_chan->global_rc == 1) {
// if global reference count is one, then pt is the only
// thread knowing the channel, hence the try is DISABLED.
*try_result = PICC_TRY_DISABLED;
return NULL;
}
PICC_Commit * commit = NULL;
PICC_CommitStatus ok = PICC_CANNOT_ACQUIRE;
do {
// search for a valid input commitment
commit = PICC_fetch_input_commitment(out_chan);
if(commit == NULL) {
// if no valid or invalid commitment left, need to
// make an output commitment
*try_result = PICC_TRY_COMMIT;
return NULL;
}
// here, we have a candidate input commitment
// try to awake the commiting thread
do {
ok = PICC_can_awake(commit->thread, commit);
if(ok == PICC_CANNOT_ACQUIRE) {
// to avoid contention on thread awaking
PICC_low_level_yield();
}
} while(ok == PICC_CANNOT_ACQUIRE);
// here we have either a valid commitment
// an an awoken thread, or an invalid commitment
// that we just removed (lazy deletion).
if (ok == PICC_VALID_COMMIT) {
// ok, everything's fine a synchronization will occur
*try_result = PICC_TRY_ENABLED;
return commit; // we return the valid commitment
}
// otherwise it's invalid and deleted, and we will
// try to find a further commitment
} while (!(PICC_commit_list_is_empty(out_chan->incommits)));
// TODO: raise a "dead code reached" error
CRASH_NEW_ERROR(ERR_DEAD_CODE_REACHED);
return NULL;
}
