Add barriers

[urcu.git] / urcu.h

diff --git a/urcu.h b/urcu.h
index 92b31df603d157ffa942534af1d5731d912c2342..3eca5ea3c44ccc7135635229c41141d5050df1e2 100644 (file)
--- a/urcu.h
+++ b/urcu.h
@@ -130,6 +130,13 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr,
 
 #define SIGURCU SIGUSR1
 
+/*
+ * If a reader is really non-cooperative and refuses to commit its
+ * urcu_active_readers count to memory (there is no barrier in the reader
+ * per-se), kick it after a few loops waiting for it.
+ */
+#define KICK_READER_LOOPS 10000
+
 #ifdef DEBUG_YIELD
 #include <sched.h>
 #include <time.h>
@@ -219,13 +226,11 @@ static inline int rcu_old_gp_ongoing(long *value)
 
        if (value == NULL)
                return 0;
-       debug_yield_write();
        /*
         * Make sure both tests below are done on the same version of *value
         * to insure consistency.
         */
        v = ACCESS_ONCE(*value);
-       debug_yield_write();
        return (v & RCU_GP_CTR_NEST_MASK) &&
                 ((v ^ urcu_gp_ctr) & RCU_GP_CTR_BIT);
 }
@@ -234,34 +239,29 @@ static inline void rcu_read_lock(void)
 {
        long tmp;
 
-       debug_yield_read();
        tmp = urcu_active_readers;
-       debug_yield_read();
        /* urcu_gp_ctr = RCU_GP_COUNT | (~RCU_GP_CTR_BIT or RCU_GP_CTR_BIT) */
+       /* The data dependency "read urcu_gp_ctr, write urcu_active_readers",
+        * serializes those two memory operations. */
        if (likely(!(tmp & RCU_GP_CTR_NEST_MASK)))
                urcu_active_readers = urcu_gp_ctr;
        else
                urcu_active_readers = tmp + RCU_GP_COUNT;
-       debug_yield_read();
        /*
         * Increment active readers count before accessing the pointer.
         * See force_mb_all_threads().
         */
        read_barrier();
-       debug_yield_read();
 }
 
 static inline void rcu_read_unlock(void)
 {
-       debug_yield_read();
        read_barrier();
-       debug_yield_read();
        /*
         * Finish using rcu before decrementing the pointer.
         * See force_mb_all_threads().
         */
        urcu_active_readers -= RCU_GP_COUNT;
-       debug_yield_read();
 }
 
 /**
@@ -302,7 +302,6 @@ extern void synchronize_rcu(void);
 #define urcu_publish_content(p, v) \
        ({ \
                void *oldptr; \
-               debug_yield_write(); \
                oldptr = rcu_xchg_pointer(p, v); \
                synchronize_rcu(); \
                oldptr; \