/* This function is used to run a function from the main thread.
Sync_func is the function pointer that will run from main thread
The function can have two long in parameters and must return long */
long g_xrdp_sync(long(*sync_func)(long param1, long param2), long sync_param1, long sync_param2)
{
long sync_result;
int sync_command;
/* If the function is called from the main thread, the function can
* be called directly. g_threadid= main thread ID*/
if (tc_threadid_equal(tc_get_threadid(), g_threadid))
{
/* this is the main thread, call the function directly */
/* in fork mode, this always happens too */
sync_result = sync_func(sync_param1, sync_param2);
/*g_writeln("g_xrdp_sync processed IN main thread -> continue");*/
}
else
{
/* All threads have to wait here until the main thread
* process the function. g_process_waiting_function() is called
* from the listening thread. g_process_waiting_function() process the function*/
tc_mutex_lock(g_sync1_mutex);
tc_mutex_lock(g_sync_mutex);
g_sync_param1 = sync_param1;
g_sync_param2 = sync_param2;
g_sync_func = sync_func;
/* set a value THREAD_WAITING so the g_process_waiting_function function
* know if any function must be processed */
g_sync_command = THREAD_WAITING;
tc_mutex_unlock(g_sync_mutex);
/* set this event so that the main thread know if
* g_process_waiting_function() must be called */
SetEvent(g_SyncEvent);
do
{
g_sleep(100);
tc_mutex_lock(g_sync_mutex);
/* load new value from global to see if the g_process_waiting_function()
* function has processed the function */
sync_command = g_sync_command;
sync_result = g_sync_result;
tc_mutex_unlock(g_sync_mutex);
} while (sync_command != 0); /* loop until g_process_waiting_function()
* has processed the request */
tc_mutex_unlock(g_sync1_mutex);
/*g_writeln("g_xrdp_sync processed BY main thread -> continue");*/
}
return sync_result;
}
long APP_CC
g_xrdp_sync(long (*sync_func)(long param1, long param2), long sync_param1,
long sync_param2)
{
long sync_result;
int sync_command;
if (tc_threadid_equal(tc_get_threadid(), g_threadid))
{
/* this is the main thread, call the function directly */
sync_result = sync_func(sync_param1, sync_param2);
}
else
{
tc_mutex_lock(g_sync1_mutex);
tc_mutex_lock(g_sync_mutex);
g_sync_param1 = sync_param1;
g_sync_param2 = sync_param2;
g_sync_func = sync_func;
g_sync_command = 100;
tc_mutex_unlock(g_sync_mutex);
g_set_wait_obj(g_sync_event);
do
{
g_sleep(100);
tc_mutex_lock(g_sync_mutex);
sync_command = g_sync_command;
sync_result = g_sync_result;
tc_mutex_unlock(g_sync_mutex);
}
while (sync_command != 0);
tc_mutex_unlock(g_sync1_mutex);
}
return sync_result;
}
/*
* Helper function for synchronize_srcu() and synchronize_srcu_expedited().
*/
static void __synchronize_srcu(struct srcu_struct *sp, void (*sync_func)(void))
{
int idx;
idx = sp->completed;
mutex_lock(&sp->mutex);
/*
* Check to see if someone else did the work for us while we were
* waiting to acquire the lock. We need -two- advances of
* the counter, not just one. If there was but one, we might have
* shown up -after- our helper's first synchronize_sched(), thus
* having failed to prevent CPU-reordering races with concurrent
* srcu_read_unlock()s on other CPUs (see comment below). So we
* either (1) wait for two or (2) supply the second ourselves.
*/
if ((sp->completed - idx) >= 2) {
mutex_unlock(&sp->mutex);
return;
}
sync_func(); /* Force memory barrier on all CPUs. */
/*
* The preceding synchronize_sched() ensures that any CPU that
* sees the new value of sp->completed will also see any preceding
* changes to data structures made by this CPU. This prevents
* some other CPU from reordering the accesses in its SRCU
* read-side critical section to precede the corresponding
* srcu_read_lock() -- ensuring that such references will in
* fact be protected.
*
* So it is now safe to do the flip.
*/
idx = sp->completed & 0x1;
sp->completed++;
sync_func(); /* Force memory barrier on all CPUs. */
/*
* At this point, because of the preceding synchronize_sched(),
* all srcu_read_lock() calls using the old counters have completed.
* Their corresponding critical sections might well be still
* executing, but the srcu_read_lock() primitives themselves
* will have finished executing. We initially give readers
* an arbitrarily chosen 10 microseconds to get out of their
* SRCU read-side critical sections, then loop waiting 1/HZ
* seconds per iteration. The 10-microsecond value has done
* very well in testing.
*/
if (srcu_readers_active_idx(sp, idx))
udelay(SYNCHRONIZE_SRCU_READER_DELAY);
while (srcu_readers_active_idx(sp, idx))
schedule_timeout_interruptible(1);
sync_func(); /* Force memory barrier on all CPUs. */
/*
* The preceding synchronize_sched() forces all srcu_read_unlock()
* primitives that were executing concurrently with the preceding
* for_each_possible_cpu() loop to have completed by this point.
* More importantly, it also forces the corresponding SRCU read-side
* critical sections to have also completed, and the corresponding
* references to SRCU-protected data items to be dropped.
*
* Note:
*
* Despite what you might think at first glance, the
* preceding synchronize_sched() -must- be within the
* critical section ended by the following mutex_unlock().
* Otherwise, a task taking the early exit can race
* with a srcu_read_unlock(), which might have executed
* just before the preceding srcu_readers_active() check,
* and whose CPU might have reordered the srcu_read_unlock()
* with the preceding critical section. In this case, there
* is nothing preventing the synchronize_sched() task that is
* taking the early exit from freeing a data structure that
* is still being referenced (out of order) by the task
* doing the srcu_read_unlock().
*
* Alternatively, the comparison with "2" on the early exit
* could be changed to "3", but this increases synchronize_srcu()
* latency for bulk loads. So the current code is preferred.
*/
mutex_unlock(&sp->mutex);
}