Add missing rcu_cmpxchg_pointer define

[urcu.git] / urcu-qsbr-static.h

diff --git a/urcu-qsbr-static.h b/urcu-qsbr-static.h
index 22a93b2fd7a823d21c76cbbd1ad5c6bf3b0495e4..87305cb694a9bcc4e175f37829736fcdb81d9686 100644 (file)
--- a/urcu-qsbr-static.h
+++ b/urcu-qsbr-static.h
@@ -33,6 +33,8 @@
 #include <pthread.h>
 #include <assert.h>
 #include <limits.h>
+#include <syscall.h>
+#include <unistd.h>
 
 #include <compiler.h>
 #include <arch.h>
@@ -87,6 +89,10 @@
                                (_________p1);                          \
                                })
 
+#define futex(...)             syscall(__NR_futex, __VA_ARGS__)
+#define FUTEX_WAIT             0
+#define FUTEX_WAKE             1
+
 /*
  * This code section can only be included in LGPL 2.1 compatible source code.
  * See below for the function call wrappers which can be used in code meant to
@@ -102,6 +108,11 @@
  */
 #define KICK_READER_LOOPS 10000
 
+/*
+ * Active attempts to check for reader Q.S. before calling futex().
+ */
+#define RCU_QS_ACTIVE_ATTEMPTS 100
+
 #ifdef DEBUG_RCU
 #define rcu_assert(args...)    assert(args)
 #else
@@ -173,6 +184,20 @@ extern unsigned long urcu_gp_ctr;
 
 extern unsigned long __thread rcu_reader_qs_gp;
 
+extern int gp_futex;
+
+/*
+ * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
+ */
+static inline void wake_up_gp(void)
+{
+       if (unlikely(atomic_read(&gp_futex) == -1)) {
+               atomic_set(&gp_futex, 0);
+               futex(&gp_futex, FUTEX_WAKE, 1,
+                     NULL, NULL, 0);
+       }
+}
+
 #if (BITS_PER_LONG < 64)
 static inline int rcu_gp_ongoing(unsigned long *value)
 {
@@ -208,6 +233,8 @@ static inline void _rcu_quiescent_state(void)
 {
        smp_mb();       
        _STORE_SHARED(rcu_reader_qs_gp, _LOAD_SHARED(urcu_gp_ctr));
+       smp_mb();       /* write rcu_reader_qs_gp before read futex */
+       wake_up_gp();
        smp_mb();
 }
 
@@ -215,6 +242,8 @@ static inline void _rcu_thread_offline(void)
 {
        smp_mb();
        STORE_SHARED(rcu_reader_qs_gp, 0);
+       smp_mb();       /* write rcu_reader_qs_gp before read futex */
+       wake_up_gp();
 }
 
 static inline void _rcu_thread_online(void)
@@ -244,6 +273,22 @@ static inline void _rcu_thread_online(void)
                STORE_SHARED(p, v);                     \
        })
 
+/**
+ * _rcu_cmpxchg_pointer - same as rcu_assign_pointer, but tests if the pointer
+ * is as expected by "old". If succeeds, returns the previous pointer to the
+ * data structure, which can be safely freed after waiting for a quiescent state
+ * using synchronize_rcu(). If fails (unexpected value), returns old (which
+ * should not be freed !).
+ */
+
+#define _rcu_cmpxchg_pointer(p, old, _new)             \
+       ({                                              \
+               if (!__builtin_constant_p(_new) ||      \
+                   ((_new) != NULL))                   \
+                       wmb();                          \
+               cmpxchg(p, old, _new);                  \
+       })
+
 /**
  * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
  * pointer to the data structure, which can be safely freed after waiting for a