Add sys_membarrier() dynamic detection, old liburcu.so -> liburcu-signal.so

[urcu.git] / urcu.c

diff --git a/urcu.c b/urcu.c
index c4b2b428787fbc519031f2c696773cd3300767bb..67a3eb21c8996b0751f9fc1d14ed9d71379f8bf5 100644 (file)
--- a/urcu.c
+++ b/urcu.c
@@ -23,6 +23,7 @@
  * IBM's contributions to this file may be relicensed under LGPLv2 or later.
  */
 
+#define _BSD_SOURCE
 #include <stdio.h>
 #include <pthread.h>
 #include <signal.h>
@@ -36,17 +37,26 @@
 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
 #include "urcu.h"
 
-#ifndef RCU_MB
+#ifdef RCU_MEMBARRIER
 static int init_done;
+int has_sys_membarrier;
 
 void __attribute__((constructor)) rcu_init(void);
-void __attribute__((destructor)) rcu_exit(void);
-#else
+#endif
+
+#ifdef RCU_MB
 void rcu_init(void)
 {
 }
 #endif
 
+#ifdef RCU_SIGNAL
+static int init_done;
+
+void __attribute__((constructor)) rcu_init(void);
+void __attribute__((destructor)) rcu_exit(void);
+#endif
+
 static pthread_mutex_t rcu_mutex = PTHREAD_MUTEX_INITIALIZER;
 
 int gp_futex;
@@ -118,45 +128,25 @@ static void switch_next_rcu_qparity(void)
        STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE);
 }
 
-#ifdef RCU_MB
-#if 0 /* unused */
-static void force_mb_single_thread(struct rcu_reader *index)
+#ifdef RCU_MEMBARRIER
+static void smp_mb_heavy(void)
 {
-       smp_mb();
+       if (likely(has_sys_membarrier))
+               membarrier(1);
+       else
+               smp_mb();
 }
-#endif //0
+#endif
 
-static void force_mb_all_threads(void)
-{
-       smp_mb();
-}
-#else /* #ifdef RCU_MB */
-#if 0 /* unused */
-static void force_mb_single_thread(struct rcu_reader *index)
+#ifdef RCU_MB
+static void smp_mb_heavy(void)
 {
-       assert(!list_empty(&registry));
-       /*
-        * pthread_kill has a smp_mb(). But beware, we assume it performs
-        * a cache flush on architectures with non-coherent cache. Let's play
-        * safe and don't assume anything : we use smp_mc() to make sure the
-        * cache flush is enforced.
-        */
-       index->need_mb = 1;
-       smp_mc();       /* write ->need_mb before sending the signals */
-       pthread_kill(index->tid, SIGRCU);
        smp_mb();
-       /*
-        * Wait for sighandler (and thus mb()) to execute on every thread.
-        * BUSY-LOOP.
-        */
-       while (index->need_mb) {
-               poll(NULL, 0, 1);
-       }
-       smp_mb();       /* read ->need_mb before ending the barrier */
 }
-#endif //0
+#endif
 
-static void force_mb_all_threads(void)
+#ifdef RCU_SIGNAL
+static void force_mb_all_readers(void)
 {
        struct rcu_reader *index;
 
@@ -198,7 +188,12 @@ static void force_mb_all_threads(void)
        }
        smp_mb();       /* read ->need_mb before ending the barrier */
 }
-#endif /* #else #ifdef RCU_MB */
+
+static void smp_mb_heavy(void)
+{
+       force_mb_all_readers();
+}
+#endif /* #ifdef RCU_SIGNAL */
 
 /*
  * synchronize_rcu() waiting. Single thread.
@@ -206,7 +201,7 @@ static void force_mb_all_threads(void)
 static void wait_gp(void)
 {
        /* Read reader_gp before read futex */
-       force_mb_all_threads();
+       smp_mb_heavy();
        if (uatomic_read(&gp_futex) == -1)
                futex_async(&gp_futex, FUTEX_WAIT, -1,
                      NULL, NULL, 0);
@@ -228,7 +223,7 @@ void wait_for_quiescent_state(void)
                if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
                        uatomic_dec(&gp_futex);
                        /* Write futex before read reader_gp */
-                       force_mb_all_threads();
+                       smp_mb_heavy();
                }
 
                list_for_each_entry_safe(index, tmp, &registry, head) {
@@ -240,7 +235,7 @@ void wait_for_quiescent_state(void)
                if (list_empty(&registry)) {
                        if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
                                /* Read reader_gp before write futex */
-                               force_mb_all_threads();
+                               smp_mb_heavy();
                                uatomic_set(&gp_futex, 0);
                        }
                        break;
@@ -258,7 +253,7 @@ void wait_for_quiescent_state(void)
                if (list_empty(&registry)) {
                        if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
                                /* Read reader_gp before write futex */
-                               force_mb_all_threads();
+                               smp_mb_heavy();
                                uatomic_set(&gp_futex, 0);
                        }
                        break;
@@ -268,7 +263,7 @@ void wait_for_quiescent_state(void)
                                wait_gp();
                                break; /* only escape switch */
                        case KICK_READER_LOOPS:
-                               force_mb_all_threads();
+                               smp_mb_heavy();
                                wait_loops = 0;
                                break; /* only escape switch */
                        default:
@@ -289,7 +284,7 @@ void synchronize_rcu(void)
         * where new ptr points to. Must be done within internal_rcu_lock
         * because it iterates on reader threads.*/
        /* Write new ptr before changing the qparity */
-       force_mb_all_threads();
+       smp_mb_heavy();
 
        switch_next_rcu_qparity();      /* 0 -> 1 */
 
@@ -353,7 +348,7 @@ void synchronize_rcu(void)
        /* Finish waiting for reader threads before letting the old ptr being
         * freed. Must be done within internal_rcu_lock because it iterates on
         * reader threads. */
-       force_mb_all_threads();
+       smp_mb_heavy();
 
        internal_rcu_unlock();
 }
@@ -391,7 +386,18 @@ void rcu_unregister_thread(void)
        internal_rcu_unlock();
 }
 
-#ifndef RCU_MB
+#ifdef RCU_MEMBARRIER
+void rcu_init(void)
+{
+       if (init_done)
+               return;
+       init_done = 1;
+       if (!membarrier(1))
+               has_sys_membarrier = 1;
+}
+#endif
+
+#ifdef RCU_SIGNAL
 static void sigrcu_handler(int signo, siginfo_t *siginfo, void *context)
 {
        /*
@@ -444,4 +450,4 @@ void rcu_exit(void)
        assert(act.sa_sigaction == sigrcu_handler);
        assert(list_empty(&registry));
 }
-#endif /* #ifndef RCU_MB */
+#endif /* #ifdef RCU_SIGNAL */