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.

include/common/hathreads.h

@@ -60,6 +60,15 @@ extern THREAD_LOCAL unsigned int tid_bit; /* The bit corresponding to the thread
 		*(val);							\
 	})
 
+
+#define THREAD_SYNC_INIT(m)  do { /* do nothing */ } while(0)
+#define THREAD_SYNC_ENABLE() do { /* do nothing */ } while(0)
+#define THREAD_WANT_SYNC()   do { /* do nothing */ } while(0)
+#define THREAD_ENTER_SYNC()  do { /* do nothing */ } while(0)
+#define THREAD_EXIT_SYNC()   do { /* do nothing */ } while(0)
+#define THREAD_NO_SYNC()     ({ 0; })
+#define THREAD_NEED_SYNC()   ({ 1; })
+
 #define SPIN_INIT(l)         do { /* do nothing */ } while(0)
 #define SPIN_DESTROY(l)      do { /* do nothing */ } while(0)
 #define SPIN_LOCK(lbl, l)    do { /* do nothing */ } while(0)
@@ -109,10 +118,27 @@ extern THREAD_LOCAL unsigned int tid_bit; /* The bit corresponding to the thread
 		(*val);							\
 	})
 
+#define THREAD_SYNC_INIT(m)   thread_sync_init(m)
+#define THREAD_SYNC_ENABLE()  thread_sync_enable()
+#define THREAD_WANT_SYNC()    thread_want_sync()
+#define THREAD_ENTER_SYNC()   thread_enter_sync()
+#define THREAD_EXIT_SYNC()    thread_exit_sync()
+#define THREAD_NO_SYNC()      thread_no_sync()
+#define THREAD_NEED_SYNC()    thread_need_sync()
+
+int  thread_sync_init(unsigned long mask);
+void thread_sync_enable(void);
+void thread_want_sync(void);
+void thread_enter_sync(void);
+void thread_exit_sync(void);
+int  thread_no_sync(void);
+int  thread_need_sync(void);
+
 #if defined(DEBUG_THREAD) || defined(DEBUG_FULL)
 
 enum lock_label {
-	LOCK_LABELS = 0
+	THREAD_SYNC_LOCK = 0,
+	LOCK_LABELS
 };
 struct lock_stat {
 	uint64_t nsec_wait_for_write;
@@ -194,7 +220,7 @@ struct ha_rwlock {
 
 static inline void show_lock_stats()
 {
-	const char *labels[LOCK_LABELS] = {};
+	const char *labels[LOCK_LABELS] = {"THREAD_SYNC" };
 	int lbl;
 
 	for (lbl = 0; lbl < LOCK_LABELS; lbl++) {

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