MEDIUM: threads: Adds a set of functions to handle sync-point
A sync-point is a protected area where you have the warranty that no concurrency
access is possible. It is implementated as a thread barrier to enter in the
sync-point and another one to exit from it. Inside the sync-point, all threads
that must do some syncrhonous processing will be called one after the other
while all other threads will wait. All threads will then exit from the
sync-point at the same time.
A sync-point will be evaluated only when necessary because it is a costly
operation. To limit the waiting time of each threads, we must have a mechanism
to wakeup all threads. This is done with a pipe shared by all threads. By
writting in this pipe, we will interrupt all threads blocked on a poller. The
pipe is then flushed before exiting from the sync-point.
diff --git a/src/hathreads.c b/src/hathreads.c
index ea48ce5..4c795b1 100644
--- a/src/hathreads.c
+++ b/src/hathreads.c
@@ -10,25 +10,150 @@
*
*/
+#include <unistd.h>
+#include <fcntl.h>
+
#include <common/hathreads.h>
+#include <common/standard.h>
+#include <proto/fd.h>
THREAD_LOCAL unsigned int tid = 0;
THREAD_LOCAL unsigned int tid_bit = (1UL << 0);
#ifdef USE_THREAD
+static HA_SPINLOCK_T sync_lock;
+static int threads_sync_pipe[2];
+static unsigned long threads_want_sync = 0;
+static unsigned long all_threads_mask = 0;
+
#if defined(DEBUG_THREAD) || defined(DEBUG_FULL)
struct lock_stat lock_stats[LOCK_LABELS];
#endif
+/* Dummy I/O handler used by the sync pipe.*/
+static void thread_sync_io_handler(int fd) { }
+
+/* Initializes the sync point. It creates a pipe used by threads to wakup all
+ * others when a sync is requested. It also initialize the mask of all create
+ * threads. It returns 0 on success and -1 if an error occurred.
+ */
+int thread_sync_init(unsigned long mask)
+{
+ int rfd;
+
+ if (pipe(threads_sync_pipe) < 0)
+ return -1;
+
+ rfd = threads_sync_pipe[0];
+ fcntl(rfd, F_SETFL, O_NONBLOCK);
+
+ fdtab[rfd].owner = NULL;
+ fdtab[rfd].iocb = thread_sync_io_handler;
+ fd_insert(rfd);
+
+ all_threads_mask = mask;
+ return 0;
+}
+
+/* Enables the sync point. */
+void thread_sync_enable(void)
+{
+ fd_want_recv(threads_sync_pipe[0]);
+}
+
+/* Called when a thread want to pass into the sync point. It subscribes the
+ * current thread in threads waiting for sync by update a bit-field. It this is
+ * the first one, it wakeup all other threads by writing on the sync pipe.
+ */
+void thread_want_sync()
+{
+ if (all_threads_mask) {
+ if (HA_ATOMIC_OR(&threads_want_sync, tid_bit) == tid_bit)
+ shut_your_big_mouth_gcc(write(threads_sync_pipe[1], "S", 1));
+ }
+ else {
+ threads_want_sync = 1;
+ }
+}
+
+/* Returns 1 if no thread has requested a sync. Otherwise, it returns 0. */
+int thread_no_sync()
+{
+ return (threads_want_sync == 0);
+}
+
+/* Returns 1 if the current thread has requested a sync. Otherwise, it returns
+ * 0.
+ */
+int thread_need_sync()
+{
+ return (threads_want_sync & tid_bit);
+}
+
+/* Thread barrier. Synchronizes all threads at the barrier referenced by
+ * <barrier>. The calling thread shall block until all other threads have called
+ * thread_sync_barrier specifying the same barrier.
+ *
+ * If you need to use several barriers at differnt points, you need to use a
+ * different <barrier> for each point.
+ */
+static inline void thread_sync_barrier(volatile unsigned long *barrier)
+{
+ unsigned long old = all_threads_mask;
+
+ HA_ATOMIC_CAS(barrier, &old, 0);
+ HA_ATOMIC_OR(barrier, tid_bit;
+ while (*barrier != all_threads_mask)
+ pl_cpu_relax();
+}
+
+/* Enter into the sync point and lock it if the current thread has requested a
+ * sync. */
+void thread_enter_sync()
+{
+ static volatile unsigned long barrier = 0;
+
+ if (!all_threads_mask)
+ return;
+
+ thread_sync_barrier(&barrier);
+ if (threads_want_sync & tid_bit)
+ SPIN_LOCK(THREAD_SYNC_LOCK, &sync_lock);
+}
+
+/* Exit from the sync point and unlock it if it was previously locked. If the
+ * current thread is the last one to have requested a sync, the sync pipe is
+ * flushed.
+ */
+void thread_exit_sync()
+{
+ static volatile unsigned long barrier = 0;
+
+ if (!all_threads_mask)
+ return;
+
+ if (threads_want_sync & tid_bit)
+ SPIN_UNLOCK(THREAD_SYNC_LOCK, &sync_lock);
+
+ if (HA_ATOMIC_AND(&threads_want_sync, ~tid_bit) == 0) {
+ char c;
+
+ shut_your_big_mouth_gcc(read(threads_sync_pipe[0], &c, 1));
+ fd_done_recv(threads_sync_pipe[0]);
+ }
+
+ thread_sync_barrier(&barrier);
+}
+
+
__attribute__((constructor))
static void __hathreads_init(void)
{
-
+ SPIN_INIT(&sync_lock);
#if defined(DEBUG_THREAD) || defined(DEBUG_FULL)
memset(lock_stats, 0, sizeof(lock_stats));
#endif
-
}
#endif