/*
- * urcu.c
+ * urcu-qsbr.c
*
- * Userspace RCU library
+ * Userspace RCU QSBR library
*
* Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
* Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
#include <string.h>
#include <errno.h>
#include <poll.h>
+#include <unistd.h>
-#include "urcu-static.h"
+#define BUILD_QSBR_LIB
+#include "urcu-qsbr-static.h"
/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
-#include "urcu.h"
+#include "urcu-qsbr.h"
-pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
+static pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
/*
* Global grace period counter.
*/
-long urcu_gp_ctr = 0;
+unsigned long urcu_gp_ctr = RCU_GP_ONLINE;
/*
* Written to only by each individual reader. Read by both the reader and the
* writers.
*/
-long __thread urcu_active_readers;
+struct urcu_reader_status __thread urcu_reader_status;
/* Thread IDs of registered readers */
#define INIT_NUM_THREADS 4
struct reader_registry {
pthread_t tid;
- long *urcu_active_readers;
- char *need_mb;
+ struct urcu_reader_status *urcu_reader_status;
};
#ifdef DEBUG_YIELD
#endif
static struct reader_registry *registry;
-static char __thread need_mb;
static int num_readers, alloc_readers;
-void internal_urcu_lock(void)
+static void internal_urcu_lock(void)
{
int ret;
perror("Error in pthread mutex lock");
exit(-1);
}
- if (need_mb) {
- smp_mb();
- need_mb = 0;
- smp_mb();
- }
poll(NULL,0,10);
}
#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
}
-void internal_urcu_unlock(void)
+static void internal_urcu_unlock(void)
{
int ret;
}
}
-#ifdef HAS_INCOHERENT_CACHES
-static void force_mb_single_thread(struct reader_registry *index)
-{
- smp_mb();
-}
-#endif /* #ifdef HAS_INCOHERENT_CACHES */
-
-static void force_mb_all_threads(void)
-{
- smp_mb();
-}
-
-void wait_for_quiescent_state(void)
+/*
+ * synchronize_rcu() waiting. Single thread.
+ */
+static void wait_for_quiescent_state(void)
{
struct reader_registry *index;
if (!registry)
return;
/*
- * Wait for each thread urcu_active_readers count to become 0.
+ * Wait for each thread rcu_reader qs_gp count to become 0.
*/
for (index = registry; index < registry + num_readers; index++) {
-#ifndef HAS_INCOHERENT_CACHES
- while (rcu_old_gp_ongoing(index->urcu_active_readers))
- cpu_relax();
-#else /* #ifndef HAS_INCOHERENT_CACHES */
int wait_loops = 0;
- /*
- * BUSY-LOOP. Force the reader thread to commit its
- * urcu_active_readers update to memory if we wait for too long.
- */
- while (rcu_old_gp_ongoing(index->urcu_active_readers)) {
- if (wait_loops++ == KICK_READER_LOOPS) {
- force_mb_single_thread(index);
+
+ if (likely(!rcu_gp_ongoing(&index->urcu_reader_status->qs_gp)))
+ continue;
+
+ index->urcu_reader_status->gp_waiting = 1;
+ while (rcu_gp_ongoing(&index->urcu_reader_status->qs_gp)) {
+ if (wait_loops++ == RCU_QS_ACTIVE_ATTEMPTS) {
+ /* adapted wait time, in us */
+ usleep(LOAD_SHARED(index->urcu_reader_status->qs_time_delta_usec) / 4);
wait_loops = 0;
} else {
+#ifndef HAS_INCOHERENT_CACHES
cpu_relax();
+#else /* #ifndef HAS_INCOHERENT_CACHES */
+ smp_mb();
+#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
}
}
-#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
+ index->urcu_reader_status->gp_waiting = 0;
}
}
+/*
+ * Using a two-subphases algorithm for architectures with smaller than 64-bit
+ * long-size to ensure we do not encounter an overflow bug.
+ */
+
+#if (BITS_PER_LONG < 64)
+/*
+ * called with urcu_mutex held.
+ */
+static void switch_next_urcu_qparity(void)
+{
+ STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_CTR);
+}
+
+void synchronize_rcu(void)
+{
+ unsigned long was_online;
+
+ was_online = urcu_reader_status.qs_gp;
+
+ /* All threads should read qparity before accessing data structure
+ * where new ptr points to.
+ */
+ /* Write new ptr before changing the qparity */
+ smp_mb();
+
+ /*
+ * Mark the writer thread offline to make sure we don't wait for
+ * our own quiescent state. This allows using synchronize_rcu() in
+ * threads registered as readers.
+ */
+ if (was_online)
+ STORE_SHARED(urcu_reader_status.qs_gp, 0);
+
+ internal_urcu_lock();
+
+ STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_ONGOING);
+
+ switch_next_urcu_qparity(); /* 0 -> 1 */
+
+ /*
+ * Must commit qparity update to memory before waiting for parity
+ * 0 quiescent state. Failure to do so could result in the writer
+ * waiting forever while new readers are always accessing data (no
+ * progress).
+ * Ensured by STORE_SHARED and LOAD_SHARED.
+ */
+
+ /*
+ * Wait for previous parity to be empty of readers.
+ */
+ wait_for_quiescent_state(); /* Wait readers in parity 0 */
+
+ /*
+ * Must finish waiting for quiescent state for parity 0 before
+ * committing qparity update to memory. Failure to do so could result in
+ * the writer waiting forever while new readers are always accessing
+ * data (no progress).
+ * Ensured by STORE_SHARED and LOAD_SHARED.
+ */
+
+ switch_next_urcu_qparity(); /* 1 -> 0 */
+
+ /*
+ * Must commit qparity update to memory before waiting for parity
+ * 1 quiescent state. Failure to do so could result in the writer
+ * waiting forever while new readers are always accessing data (no
+ * progress).
+ * Ensured by STORE_SHARED and LOAD_SHARED.
+ */
+
+ /*
+ * Wait for previous parity to be empty of readers.
+ */
+ wait_for_quiescent_state(); /* Wait readers in parity 1 */
+
+ STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_ONGOING);
+
+ internal_urcu_unlock();
+
+ /*
+ * Finish waiting for reader threads before letting the old ptr being
+ * freed.
+ */
+ if (was_online)
+ _STORE_SHARED(urcu_reader_status.qs_gp,
+ LOAD_SHARED(urcu_gp_ctr));
+ smp_mb();
+}
+#else /* !(BITS_PER_LONG < 64) */
void synchronize_rcu(void)
{
+ unsigned long was_online;
+
+ was_online = urcu_reader_status.qs_gp;
+
+ /*
+ * Mark the writer thread offline to make sure we don't wait for
+ * our own quiescent state. This allows using synchronize_rcu() in
+ * threads registered as readers.
+ */
+ smp_mb();
+ if (was_online)
+ STORE_SHARED(urcu_reader_status.qs_gp, 0);
+
internal_urcu_lock();
- force_mb_all_threads();
- urcu_gp_ctr += 2;
+ STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_ONGOING);
+ STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr + RCU_GP_CTR);
wait_for_quiescent_state();
- force_mb_all_threads();
+ STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_ONGOING);
internal_urcu_unlock();
+
+ if (was_online)
+ _STORE_SHARED(urcu_reader_status.qs_gp,
+ LOAD_SHARED(urcu_gp_ctr));
+ smp_mb();
}
+#endif /* !(BITS_PER_LONG < 64) */
/*
* library wrappers to be used by non-LGPL compatible source code.
return STORE_SHARED(p, v);
}
+void *rcu_cmpxchg_pointer_sym(void **p, void *old, void *_new)
+{
+ wmb();
+ return cmpxchg(p, old, _new);
+}
+
void *rcu_xchg_pointer_sym(void **p, void *v)
{
wmb();
return oldptr;
}
+void rcu_quiescent_state(void)
+{
+ _rcu_quiescent_state();
+}
+
+void rcu_thread_offline(void)
+{
+ _rcu_thread_offline();
+}
+
+void rcu_thread_online(void)
+{
+ _rcu_thread_online();
+}
+
static void rcu_add_reader(pthread_t id)
{
struct reader_registry *oldarray;
}
registry[num_readers].tid = id;
/* reference to the TLS of _this_ reader thread. */
- registry[num_readers].urcu_active_readers = &urcu_active_readers;
- registry[num_readers].need_mb = &need_mb;
+ registry[num_readers].urcu_reader_status = &urcu_reader_status;
num_readers++;
}
memcpy(index, ®istry[num_readers - 1],
sizeof(struct reader_registry));
registry[num_readers - 1].tid = 0;
- registry[num_readers - 1].urcu_active_readers = NULL;
+ registry[num_readers - 1].urcu_reader_status = NULL;
num_readers--;
return;
}
internal_urcu_lock();
rcu_add_reader(pthread_self());
internal_urcu_unlock();
+ _rcu_thread_online();
}
void rcu_unregister_thread(void)
{
+ /*
+ * We have to make the thread offline otherwise we end up dealocking
+ * with a waiting writer.
+ */
+ _rcu_thread_offline();
internal_urcu_lock();
rcu_remove_reader(pthread_self());
internal_urcu_unlock();