#include <stdlib.h>
#include <pthread.h>
#include <assert.h>
+#include <limits.h>
+#include <syscall.h>
+#include <unistd.h>
-#include <compiler.h>
-#include <arch.h>
+#include <urcu/compiler.h>
+#include <urcu/arch.h>
+#include <urcu/arch_uatomic.h>
+#include <urcu/list.h>
/*
* Identify a shared load. A smp_rmc() or smp_mc() should come before the load.
(_________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
/*
* If a reader is really non-cooperative and refuses to commit its
- * rcu_reader_qs_gp count to memory (there is no barrier in the reader
+ * urcu_reader.ctr 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
+/*
+ * 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
smp_mb();
}
+#define RCU_GP_ONLINE (1UL << 0)
+#define RCU_GP_CTR (1UL << 1)
+
/*
* Global quiescent period counter with low-order bits unused.
* Using a int rather than a char to eliminate false register dependencies
* causing stalls on some architectures.
*/
-extern long urcu_gp_ctr;
+extern unsigned long urcu_gp_ctr;
+
+struct urcu_reader {
+ /* Data used by both reader and synchronize_rcu() */
+ unsigned long ctr;
+ /* Data used for registry */
+ struct list_head head __attribute__((aligned(CACHE_LINE_SIZE)));
+ pthread_t tid;
+};
+
+extern struct urcu_reader __thread urcu_reader;
+
+extern int gp_futex;
+
+/*
+ * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
+ */
+static inline void wake_up_gp(void)
+{
+ if (unlikely(uatomic_read(&gp_futex) == -1)) {
+ uatomic_set(&gp_futex, 0);
+ futex(&gp_futex, FUTEX_WAKE, 1,
+ NULL, NULL, 0);
+ }
+}
-extern long __thread rcu_reader_qs_gp;
+#if (BITS_PER_LONG < 64)
+static inline int rcu_gp_ongoing(unsigned long *value)
+{
+ unsigned long reader_gp;
-static inline int rcu_gp_ongoing(long *value)
+ if (value == NULL)
+ return 0;
+ reader_gp = LOAD_SHARED(*value);
+ return reader_gp && ((reader_gp ^ urcu_gp_ctr) & RCU_GP_CTR);
+}
+#else /* !(BITS_PER_LONG < 64) */
+static inline int rcu_gp_ongoing(unsigned long *value)
{
- long reader_gp;
+ unsigned long reader_gp;
if (value == NULL)
return 0;
reader_gp = LOAD_SHARED(*value);
- return reader_gp && (reader_gp - urcu_gp_ctr < 0);
+ return reader_gp && (reader_gp - urcu_gp_ctr > ULONG_MAX / 2);
}
+#endif /* !(BITS_PER_LONG < 64) */
static inline void _rcu_read_lock(void)
{
- rcu_assert(rcu_reader_qs_gp & 1);
+ rcu_assert(urcu_reader.ctr);
}
static inline void _rcu_read_unlock(void)
static inline void _rcu_quiescent_state(void)
{
smp_mb();
- _STORE_SHARED(rcu_reader_qs_gp, _LOAD_SHARED(urcu_gp_ctr));
+ _STORE_SHARED(urcu_reader.ctr, _LOAD_SHARED(urcu_gp_ctr));
+ smp_mb(); /* write urcu_reader.ctr before read futex */
+ wake_up_gp();
smp_mb();
}
static inline void _rcu_thread_offline(void)
{
smp_mb();
- STORE_SHARED(rcu_reader_qs_gp, 0);
+ STORE_SHARED(urcu_reader.ctr, 0);
+ smp_mb(); /* write urcu_reader.ctr before read futex */
+ wake_up_gp();
}
static inline void _rcu_thread_online(void)
{
- _STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr));
+ _STORE_SHARED(urcu_reader.ctr, LOAD_SHARED(urcu_gp_ctr));
smp_mb();
}
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(); \
+ uatomic_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
if (!__builtin_constant_p(v) || \
((v) != NULL)) \
wmb(); \
- xchg(p, v); \
+ uatomic_xchg(p, v); \
})
/*