#include <stdlib.h>
#include <pthread.h>
#include <assert.h>
+#include <limits.h>
+#include <syscall.h>
+#include <unistd.h>
-#include <compiler.h>
-#include <arch.h>
-
-/*
- * Identify a shared load. A smp_rmc() or smp_mc() should come before the load.
- */
-#define _LOAD_SHARED(p) ACCESS_ONCE(p)
-
-/*
- * Load a data from shared memory, doing a cache flush if required.
- */
-#define LOAD_SHARED(p) \
- ({ \
- smp_rmc(); \
- _LOAD_SHARED(p); \
- })
-
-/*
- * Identify a shared store. A smp_wmc() or smp_mc() should follow the store.
- */
-#define _STORE_SHARED(x, v) ({ ACCESS_ONCE(x) = (v); })
-
-/*
- * Store v into x, where x is located in shared memory. Performs the required
- * cache flush after writing. Returns v.
- */
-#define STORE_SHARED(x, v) \
- ({ \
- _STORE_SHARED(x, v); \
- smp_wmc(); \
- (v); \
- })
-
-/**
- * _rcu_dereference - reads (copy) a RCU-protected pointer to a local variable
- * into a RCU read-side critical section. The pointer can later be safely
- * dereferenced within the critical section.
- *
- * This ensures that the pointer copy is invariant thorough the whole critical
- * section.
- *
- * Inserts memory barriers on architectures that require them (currently only
- * Alpha) and documents which pointers are protected by RCU.
- *
- * Should match rcu_assign_pointer() or rcu_xchg_pointer().
- */
+#include <urcu/compiler.h>
+#include <urcu/arch.h>
+#include <urcu/system.h>
+#include <urcu/uatomic_arch.h>
+#include <urcu/list.h>
+#include <urcu/urcu-futex.h>
-#define _rcu_dereference(p) ({ \
- typeof(p) _________p1 = LOAD_SHARED(p); \
- smp_read_barrier_depends(); \
- (_________p1); \
- })
+#ifdef __cplusplus
+extern "C" {
+#endif
/*
* This code section can only be included in LGPL 2.1 compatible source code.
/*
* 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 long __thread rcu_reader_qs_gp;
+extern struct urcu_reader __thread urcu_reader;
-static inline int rcu_gp_ongoing(long *value)
+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_noasync(&gp_futex, FUTEX_WAKE, 1,
+ NULL, NULL, 0);
+ }
+}
+
+#if (BITS_PER_LONG < 64)
+static inline int rcu_gp_ongoing(unsigned long *value)
{
+ unsigned long reader_gp;
+
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)
+{
+ unsigned long reader_gp;
- return LOAD_SHARED(*value) & 1;
+ if (value == NULL)
+ return 0;
+ reader_gp = LOAD_SHARED(*value);
+ 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();
- rcu_reader_qs_gp = ACCESS_ONCE(urcu_gp_ctr) + 1;
+ _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();
- 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)
{
- rcu_reader_qs_gp = ACCESS_ONCE(urcu_gp_ctr) + 1;
+ _STORE_SHARED(urcu_reader.ctr, LOAD_SHARED(urcu_gp_ctr));
smp_mb();
}
-/**
- * _rcu_assign_pointer - assign (publicize) a pointer to a new data structure
- * meant to be read by RCU read-side critical sections. Returns the assigned
- * value.
- *
- * Documents which pointers will be dereferenced by RCU read-side critical
- * sections and adds the required memory barriers on architectures requiring
- * them. It also makes sure the compiler does not reorder code initializing the
- * data structure before its publication.
- *
- * Should match rcu_dereference_pointer().
- */
-
-#define _rcu_assign_pointer(p, v) \
- ({ \
- if (!__builtin_constant_p(v) || \
- ((v) != NULL)) \
- wmb(); \
- STORE_SHARED(p, v); \
- })
-
-/**
- * _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
- * quiescent state using synchronize_rcu().
- */
-
-#define _rcu_xchg_pointer(p, v) \
- ({ \
- if (!__builtin_constant_p(v) || \
- ((v) != NULL)) \
- wmb(); \
- xchg(p, v); \
- })
-
-/*
- * Exchanges the pointer and waits for quiescent state.
- * The pointer returned can be freed.
- */
-#define _rcu_publish_content(p, v) \
- ({ \
- void *oldptr; \
- oldptr = _rcu_xchg_pointer(p, v); \
- synchronize_rcu(); \
- oldptr; \
- })
+#ifdef __cplusplus
+}
+#endif
#endif /* _URCU_QSBR_STATIC_H */
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