urcu-ht: work in progress RCU hash table
authorMathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Sun, 27 Sep 2009 04:02:21 +0000 (00:02 -0400)
committerMathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Sun, 27 Sep 2009 04:02:21 +0000 (00:02 -0400)
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Makefile.inc
tests/Makefile.inc
tests/test_ht.c [new file with mode: 0644]
urcu-hash.c [deleted file]
urcu-ht.c [new file with mode: 0644]
urcu-ht.h [new file with mode: 0644]

index 9d566b7abded1743775a9bc6037242e313e1855b..7a5ed3f6d4b758f7405e0193e519cec037907813 100644 (file)
@@ -8,7 +8,7 @@ all: checkarch liburcu.so urcu.o \
        liburcu-mb.so urcu-mb.o \
        liburcu-defer.so urcu-defer.o \
        urcu-yield.o \
-       urcu-hash.o \
+       urcu-ht.o \
        subdirs
 
 checkarch:
index f62256bda83ef83ecc882c73db480e5e6640802d..4e853526f7fc3211427523eed816b73824917419 100644 (file)
@@ -16,6 +16,7 @@ URCU_SIGNAL_YIELD=${LIBDIR}/urcu-yield.o ${LIBDIR}/urcu.h
 URCU_MB=${LIBDIR}/urcu-mb.o ${LIBDIR}/urcu.h
 URCU_QSBR=${LIBDIR}/urcu-qsbr.o ${LIBDIR}/urcu-qsbr.h
 URCU_MB_DEFER=${LIBDIR}/urcu-mb.o ${LIBDIR}/urcu-defer.o ${LIBDIR}/urcu.h
+URCU_HT=${LIBDIR}/urcu-mb.o ${LIBDIR}/urcu-defer.o ${LIBDIR}/urcu-ht.o ${LIBDIR}/urcu.h
 
 all: test_urcu test_urcu_dynamic_link test_urcu_timing \
        test_rwlock_timing test_rwlock test_perthreadlock_timing \
@@ -24,7 +25,7 @@ all: test_urcu test_urcu_dynamic_link test_urcu_timing \
        urcutorture-yield test_mutex test_looplen test_urcu_gc \
        test_urcu_gc_mb test_qsbr_gc test_qsbr_lgc test_urcu_lgc \
        test_urcu_lgc_mb test_qsbr_dynamic_link test_urcu_mb_defer \
-       test_atomic
+       test_atomic test_ht
 
 api.h: ${APIHEADER}
        cp -f ${APIHEADER} api.h
@@ -112,6 +113,9 @@ urcutorture-yield: urcutorture.c ${URCU_SIGNAL_YIELD} rcutorture.h api.h
 test_atomic: test_atomic.c ../arch_atomic.h
        $(CC) ${CFLAGS} $(LDFLAGS) -o $@ $(SRC_DEP)
 
+test_ht: test_ht.c ${URCU_HT}
+       $(CC) ${CFLAGS} $(LDFLAGS) -o $@ $(SRC_DEP)
+
 ,PHONY: clean
 
 clean:
diff --git a/tests/test_ht.c b/tests/test_ht.c
new file mode 100644 (file)
index 0000000..12b210e
--- /dev/null
@@ -0,0 +1,434 @@
+/*
+ * test_ht.c
+ *
+ * Userspace RCU library - test program
+ *
+ * Copyright February 2009 - Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <pthread.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <assert.h>
+#include <sys/syscall.h>
+#include <sched.h>
+#include "../urcu-ht.h"
+
+#include "../arch.h"
+
+/* Make this big enough to include the POWER5+ L3 cacheline size of 256B */
+#define CACHE_LINE_SIZE 4096
+
+/* hardcoded number of CPUs */
+#define NR_CPUS 16384
+
+#if defined(_syscall0)
+_syscall0(pid_t, gettid)
+#elif defined(__NR_gettid)
+static inline pid_t gettid(void)
+{
+       return syscall(__NR_gettid);
+}
+#else
+#warning "use pid as tid"
+static inline pid_t gettid(void)
+{
+       return getpid();
+}
+#endif
+
+#ifndef DYNAMIC_LINK_TEST
+#define _LGPL_SOURCE
+#else
+#define debug_yield_read()
+#endif
+#include "../urcu.h"
+
+static struct rcu_ht *test_ht;
+
+struct test_array {
+       int a;
+};
+
+static volatile int test_go, test_stop;
+
+static unsigned long wdelay;
+
+static struct test_array *test_rcu_pointer;
+
+static unsigned long duration;
+
+/* read-side C.S. duration, in loops */
+static unsigned long rduration;
+
+static inline void loop_sleep(unsigned long l)
+{
+       while(l-- != 0)
+               cpu_relax();
+}
+
+static int verbose_mode;
+
+#define printf_verbose(fmt, args...)           \
+       do {                                    \
+               if (verbose_mode)               \
+                       printf(fmt, args);      \
+       } while (0)
+
+static unsigned int cpu_affinities[NR_CPUS];
+static unsigned int next_aff = 0;
+static int use_affinity = 0;
+
+pthread_mutex_t affinity_mutex = PTHREAD_MUTEX_INITIALIZER;
+
+static void set_affinity(void)
+{
+       cpu_set_t mask;
+       int cpu;
+       int ret;
+
+       if (!use_affinity)
+               return;
+
+       ret = pthread_mutex_lock(&affinity_mutex);
+       if (ret) {
+               perror("Error in pthread mutex lock");
+               exit(-1);
+       }
+       cpu = cpu_affinities[next_aff++];
+       ret = pthread_mutex_unlock(&affinity_mutex);
+       if (ret) {
+               perror("Error in pthread mutex unlock");
+               exit(-1);
+       }
+       CPU_ZERO(&mask);
+       CPU_SET(cpu, &mask);
+       sched_setaffinity(0, sizeof(mask), &mask);
+}
+
+/*
+ * returns 0 if test should end.
+ */
+static int test_duration_write(void)
+{
+       return !test_stop;
+}
+
+static int test_duration_read(void)
+{
+       return !test_stop;
+}
+
+static unsigned long long __thread nr_writes;
+static unsigned long long __thread nr_reads;
+
+static unsigned int nr_readers;
+static unsigned int nr_writers;
+
+pthread_mutex_t rcu_copy_mutex = PTHREAD_MUTEX_INITIALIZER;
+
+void rcu_copy_mutex_lock(void)
+{
+       int ret;
+       ret = pthread_mutex_lock(&rcu_copy_mutex);
+       if (ret) {
+               perror("Error in pthread mutex lock");
+               exit(-1);
+       }
+}
+
+void rcu_copy_mutex_unlock(void)
+{
+       int ret;
+
+       ret = pthread_mutex_unlock(&rcu_copy_mutex);
+       if (ret) {
+               perror("Error in pthread mutex unlock");
+               exit(-1);
+       }
+}
+
+/*
+ * malloc/free are reusing memory areas too quickly, which does not let us
+ * test races appropriately. Use a large circular array for allocations.
+ * ARRAY_SIZE is larger than nr_writers, which insures we never run over our tail.
+ */
+#define ARRAY_SIZE (1048576 * nr_writers)
+#define ARRAY_POISON 0xDEADBEEF
+static int array_index;
+static struct test_array *test_array;
+
+static struct test_array *test_array_alloc(void)
+{
+       struct test_array *ret;
+       int index;
+
+       rcu_copy_mutex_lock();
+       index = array_index % ARRAY_SIZE;
+       assert(test_array[index].a == ARRAY_POISON ||
+               test_array[index].a == 0);
+       ret = &test_array[index];
+       array_index++;
+       if (array_index == ARRAY_SIZE)
+               array_index = 0;
+       rcu_copy_mutex_unlock();
+       return ret;
+}
+
+static void test_array_free(struct test_array *ptr)
+{
+       if (!ptr)
+               return;
+       rcu_copy_mutex_lock();
+       ptr->a = ARRAY_POISON;
+       rcu_copy_mutex_unlock();
+}
+
+void *thr_reader(void *_count)
+{
+       unsigned long long *count = _count;
+       struct test_array *local_ptr;
+
+       printf_verbose("thread_begin %s, thread id : %lx, tid %lu\n",
+                       "reader", pthread_self(), (unsigned long)gettid());
+
+       set_affinity();
+
+       rcu_register_thread();
+
+       while (!test_go)
+       {
+       }
+       smp_mb();
+
+       for (;;) {
+               rcu_read_lock();
+               local_ptr = rcu_dereference(test_rcu_pointer);
+               debug_yield_read();
+               if (local_ptr)
+                       assert(local_ptr->a == 8);
+               if (unlikely(rduration))
+                       loop_sleep(rduration);
+               rcu_read_unlock();
+               nr_reads++;
+               if (unlikely(!test_duration_read()))
+                       break;
+       }
+
+       rcu_unregister_thread();
+
+       *count = nr_reads;
+       printf_verbose("thread_end %s, thread id : %lx, tid %lu\n",
+                       "reader", pthread_self(), (unsigned long)gettid());
+       return ((void*)1);
+
+}
+
+void *thr_writer(void *_count)
+{
+       unsigned long long *count = _count;
+       struct test_array *new, *old;
+
+       printf_verbose("thread_begin %s, thread id : %lx, tid %lu\n",
+                       "writer", pthread_self(), (unsigned long)gettid());
+
+       set_affinity();
+
+       while (!test_go)
+       {
+       }
+       smp_mb();
+
+       for (;;) {
+               new = test_array_alloc();
+               new->a = 8;
+               old = rcu_publish_content(&test_rcu_pointer, new);
+               if (old)
+                       old->a = 0;
+               test_array_free(old);
+               nr_writes++;
+               if (unlikely(!test_duration_write()))
+                       break;
+               if (unlikely(wdelay))
+                       loop_sleep(wdelay);
+       }
+
+       printf_verbose("thread_end %s, thread id : %lx, tid %lu\n",
+                       "writer", pthread_self(), (unsigned long)gettid());
+       *count = nr_writes;
+       return ((void*)2);
+}
+
+void show_usage(int argc, char **argv)
+{
+       printf("Usage : %s nr_readers nr_writers duration (s)", argv[0]);
+#ifdef DEBUG_YIELD
+       printf(" [-r] [-w] (yield reader and/or writer)");
+#endif
+       printf(" [-d delay] (writer period (us))");
+       printf(" [-c duration] (reader C.S. duration (in loops))");
+       printf(" [-v] (verbose output)");
+       printf(" [-a cpu#] [-a cpu#]... (affinity)");
+       printf("\n");
+}
+
+int main(int argc, char **argv)
+{
+       int err;
+       pthread_t *tid_reader, *tid_writer;
+       void *tret;
+       unsigned long long *count_reader, *count_writer;
+       unsigned long long tot_reads = 0, tot_writes = 0;
+       int i, a;
+
+       if (argc < 4) {
+               show_usage(argc, argv);
+               return -1;
+       }
+
+       err = sscanf(argv[1], "%u", &nr_readers);
+       if (err != 1) {
+               show_usage(argc, argv);
+               return -1;
+       }
+
+       err = sscanf(argv[2], "%u", &nr_writers);
+       if (err != 1) {
+               show_usage(argc, argv);
+               return -1;
+       }
+       
+       err = sscanf(argv[3], "%lu", &duration);
+       if (err != 1) {
+               show_usage(argc, argv);
+               return -1;
+       }
+
+       for (i = 4; i < argc; i++) {
+               if (argv[i][0] != '-')
+                       continue;
+               switch (argv[i][1]) {
+#ifdef DEBUG_YIELD
+               case 'r':
+                       yield_active |= YIELD_READ;
+                       break;
+               case 'w':
+                       yield_active |= YIELD_WRITE;
+                       break;
+#endif
+               case 'a':
+                       if (argc < i + 2) {
+                               show_usage(argc, argv);
+                               return -1;
+                       }
+                       a = atoi(argv[++i]);
+                       cpu_affinities[next_aff++] = a;
+                       use_affinity = 1;
+                       printf_verbose("Adding CPU %d affinity\n", a);
+                       break;
+               case 'c':
+                       if (argc < i + 2) {
+                               show_usage(argc, argv);
+                               return -1;
+                       }
+                       rduration = atol(argv[++i]);
+                       break;
+               case 'd':
+                       if (argc < i + 2) {
+                               show_usage(argc, argv);
+                               return -1;
+                       }
+                       wdelay = atol(argv[++i]);
+                       break;
+               case 'v':
+                       verbose_mode = 1;
+                       break;
+               }
+       }
+
+       printf_verbose("running test for %lu seconds, %u readers, %u writers.\n",
+               duration, nr_readers, nr_writers);
+       printf_verbose("Writer delay : %lu loops.\n", wdelay);
+       printf_verbose("Reader duration : %lu loops.\n", rduration);
+       printf_verbose("thread %-6s, thread id : %lx, tid %lu\n",
+                       "main", pthread_self(), (unsigned long)gettid());
+
+       test_array = malloc(sizeof(*test_array) * ARRAY_SIZE);
+       tid_reader = malloc(sizeof(*tid_reader) * nr_readers);
+       tid_writer = malloc(sizeof(*tid_writer) * nr_writers);
+       count_reader = malloc(sizeof(*count_reader) * nr_readers);
+       count_writer = malloc(sizeof(*count_writer) * nr_writers);
+       test_ht = ht_new(stupid_hash, free);
+       next_aff = 0;
+
+       for (i = 0; i < nr_readers; i++) {
+               err = pthread_create(&tid_reader[i], NULL, thr_reader,
+                                    &count_reader[i]);
+               if (err != 0)
+                       exit(1);
+       }
+       for (i = 0; i < nr_writers; i++) {
+               err = pthread_create(&tid_writer[i], NULL, thr_writer,
+                                    &count_writer[i]);
+               if (err != 0)
+                       exit(1);
+       }
+
+       smp_mb();
+
+       test_go = 1;
+
+       sleep(duration);
+
+       test_stop = 1;
+
+       for (i = 0; i < nr_readers; i++) {
+               err = pthread_join(tid_reader[i], &tret);
+               if (err != 0)
+                       exit(1);
+               tot_reads += count_reader[i];
+       }
+       for (i = 0; i < nr_writers; i++) {
+               err = pthread_join(tid_writer[i], &tret);
+               if (err != 0)
+                       exit(1);
+               tot_writes += count_writer[i];
+       }
+       ht_destroy(test_ht);
+       
+       printf_verbose("total number of reads : %llu, writes %llu\n", tot_reads,
+              tot_writes);
+       printf("SUMMARY %-25s testdur %4lu nr_readers %3u rdur %6lu "
+               "nr_writers %3u "
+               "wdelay %6lu nr_reads %12llu nr_writes %12llu nr_ops %12llu\n",
+               argv[0], duration, nr_readers, rduration,
+               nr_writers, wdelay, tot_reads, tot_writes,
+               tot_reads + tot_writes);
+       test_array_free(test_rcu_pointer);
+       free(test_array);
+       free(tid_reader);
+       free(tid_writer);
+       free(count_reader);
+       free(count_writer);
+       return 0;
+}
diff --git a/urcu-hash.c b/urcu-hash.c
deleted file mode 100644 (file)
index 1267af5..0000000
+++ /dev/null
@@ -1,230 +0,0 @@
-
-#define _LGPL_SOURCE
-#include <stdlib.h>
-#include <urcu.h>
-#include <arch.h>
-#include <arch_atomic.h>
-#include <assert.h>
-#include <compiler.h>
-#include <urcu-defer.h>
-#include <errno.h>
-
-#define HASH_SIZE      4096
-
-typedef unsigned long (*ht_hash_fct)(void *key);
-
-struct rcu_ht_node;
-
-struct rcu_ht_node {
-       struct rcu_ht_node *next;
-       void *key;
-       void *data;
-};
-
-struct rcu_ht {
-       struct rcu_ht_node *tbl[HASH_SIZE];
-       ht_hash_fct hash_fct;
-       void (*free_fct)(void *data);   /* fct to free data */
-};
-
-struct rcu_ht *ht_new(ht_hash_fct hash_fct, void (*free_fct)(void *data));
-
-void ht_delete_all(struct rcu_ht *ht);
-
-int ht_destroy(struct rcu_ht *ht);
-
-void *ht_lookup(struct rcu_ht *ht, void *key);
-
-int ht_add(struct rcu_ht *ht, void *key, void *data);
-
-int ht_delete(struct rcu_ht *ht, void *key);
-
-void *ht_steal(struct rcu_ht *ht, void *key);
-
-
-/* Implementation */
-
-static unsigned long stupid_hash(void *key)
-{
-       return (unsigned long)key % HASH_SIZE;
-}
-
-struct rcu_ht *ht_new(ht_hash_fct hash_fct, void (*free_fct)(void *data))
-{
-       struct rcu_ht *ht;
-
-       ht = calloc(1, sizeof(struct rcu_ht));
-       ht->hash_fct = hash_fct;
-       ht->free_fct = free_fct;
-}
-
-/* delete all elements */
-void ht_delete_all(struct rcu_ht *ht)
-{
-       unsigned long i;
-       struct rcu_ht_node **prev, *node;
-
-       for (i = 0; i < HASH_SIZE; i++) {
-               rcu_read_lock();
-
-               prev = &ht->tbl[i];
-               node = rcu_dereference(*prev);
-               /*
-                * Cut the head, therefore whole bucket will be unused
-                * after GP. (except for concurrent additions)
-                */
-               rcu_assign_pointer(prev, NULL);
-               for (;;) {
-                       if (likely(!node)) {
-                               break;
-                       }
-                       prev = &node->next;
-                       if (node->data)
-                               call_rcu(ht->free_fct, node->data);
-                       call_rcu(free, node);
-                       node = rcu_dereference(*prev);
-               }
-               rcu_read_unlock();
-       }
-}
-
-/*
- * Should only be called when no more concurrent readers nor writers can
- * possibly access the table.
- */
-int ht_destroy(struct rcu_ht *ht)
-{
-       ht_delete_all(ht);
-       free(ht);
-}
-
-void *ht_lookup(struct rcu_ht *ht, void *key)
-{
-       unsigned long hash;
-       struct rcu_ht_node *node;
-       void *ret;
-
-       hash = ht->hash_fct(key);
-
-       rcu_read_lock();
-       node = rcu_dereference(ht->tbl[hash]);
-       for (;;) {
-               if (likely(!node)) {
-                       ret = NULL;
-                       break;
-               }
-               if (node->key == key) {
-                       ret = node->data;
-                       break;
-               }
-               node = rcu_dereference(node->next);
-       }
-       rcu_read_unlock();
-}
-
-/*
- * Will re-try until either:
- * - The key is already there (-EEXIST)
- * - We successfully add the key at the head of a table bucket.
- */
-int ht_add(struct rcu_ht *ht, void *key, void *data)
-{
-       struct rcu_ht_node *node, *old_head, *new_head;
-       unsigned long hash;
-       int ret = 0;
-
-       new_head = calloc(1, sizeof(struct rcu_ht_node));
-       new_head->key = key;
-       new_head->data = data;
-       hash = ht->hash_fct(key);
-
-       /* here comes the fun and tricky part.
-        * Add at the beginning with a cmpxchg.
-        * Hold a read lock between the moment the first element is read
-        * and the nodes traversal (to find duplicates). This ensures
-        * the head pointer has not been reclaimed when cmpxchg is done.
-        * Always adding at the head ensures that we would have to
-        * re-try if a new item has been added concurrently. So we ensure that
-        * we never add duplicates. */
-retry:
-       rcu_read_lock();
-
-       old_head = node = rcu_dereference(ht->tbl[hash]);
-       for (;;) {
-               if (likely(!node)) {
-                       break;
-               }
-               if (node->key == key) {
-                       ret = -EEXIST;
-                       goto end;
-               }
-               node = rcu_dereference(node->next);
-       }
-       if (rcu_cmpxchg_pointer(&ht->tbl[hash], old_head, new_head) != old_head)
-               goto restart;
-end:
-       rcu_read_unlock();
-
-       return ret;
-
-       /* restart loop, release and re-take the read lock to be kind to GP */
-restart:
-       rcu_read_unlock();
-       goto retry;
-}
-
-/*
- * Restart until we successfully remove the entry, or no entry is left
- * ((void *)(unsigned long)-ENOENT).
- */
-struct rcu_ht_node *ht_steal(struct rcu_ht *ht, void *key);
-{
-       struct rcu_ht_node **prev, *node;
-       unsigned long hash;
-
-       hash = ht->hash_fct(key);
-
-retry:
-       rcu_read_lock();
-
-       prev = &ht->tbl[hash];
-       node = rcu_dereference(*prev);
-       for (;;) {
-               if (likely(!node)) {
-                       node = (void *)(unsigned long)-ENOENT;
-                       goto end;
-               }
-               if (node->key == key) {
-                       break;
-               }
-               prev = &node->next;
-               node = rcu_dereference(*prev);
-       }
-       /* Found it ! pointer to object is in "prev" */
-       if (rcu_cmpxchg_pointer(prev, node, node->next) != node)
-               goto restart;
-end:
-       rcu_read_unlock();
-
-       return node;
-
-       /* restart loop, release and re-take the read lock to be kind to GP */
-restart:
-       rcu_read_unlock();
-       goto retry;
-}
-
-int ht_delete(struct rcu_ht *ht, void *key)
-{
-       struct rcu_ht_node *node;
-
-       node = ht_steal(ht, key);
-       if (node) {
-               if (free_fct && node->data)
-                       call_rcu(ht->free_fct, node->data);
-               call_rcu(free, node);
-               return 0;
-       } else {
-               return -ENOENT;
-       }
-}
diff --git a/urcu-ht.c b/urcu-ht.c
new file mode 100644 (file)
index 0000000..8edfae3
--- /dev/null
+++ b/urcu-ht.c
@@ -0,0 +1,216 @@
+
+#define _LGPL_SOURCE
+#include <stdlib.h>
+#include <urcu.h>
+#include <arch.h>
+#include <arch_atomic.h>
+#include <assert.h>
+#include <compiler.h>
+#include <urcu-defer.h>
+#include <errno.h>
+#include <urcu-ht.h>
+
+struct rcu_ht_node;
+
+struct rcu_ht_node {
+       struct rcu_ht_node *next;
+       void *key;
+       void *data;
+};
+
+struct rcu_ht {
+       struct rcu_ht_node *tbl[HASH_SIZE];
+       ht_hash_fct hash_fct;
+       void (*free_fct)(void *data);   /* fct to free data */
+};
+
+struct rcu_ht *ht_new(ht_hash_fct hash_fct, void (*free_fct)(void *data))
+{
+       struct rcu_ht *ht;
+
+       ht = calloc(1, sizeof(struct rcu_ht));
+       ht->hash_fct = hash_fct;
+       ht->free_fct = free_fct;
+       return ht;
+}
+
+/* delete all elements */
+void ht_delete_all(struct rcu_ht *ht)
+{
+       unsigned long i;
+       struct rcu_ht_node **prev, *node;
+
+       for (i = 0; i < HASH_SIZE; i++) {
+               rcu_read_lock();
+
+               prev = &ht->tbl[i];
+               node = rcu_dereference(*prev);
+               /*
+                * Cut the head, therefore whole bucket will be unused
+                * after GP. (except for concurrent additions)
+                */
+               rcu_assign_pointer(prev, NULL);
+               for (;;) {
+                       if (likely(!node)) {
+                               break;
+                       }
+                       prev = &node->next;
+                       if (node->data)
+                               call_rcu(ht->free_fct, node->data);
+                       call_rcu(free, node);
+                       node = rcu_dereference(*prev);
+               }
+               rcu_read_unlock();
+       }
+}
+
+/*
+ * Should only be called when no more concurrent readers nor writers can
+ * possibly access the table.
+ */
+void ht_destroy(struct rcu_ht *ht)
+{
+       ht_delete_all(ht);
+       free(ht);
+}
+
+void *ht_lookup(struct rcu_ht *ht, void *key)
+{
+       unsigned long hash;
+       struct rcu_ht_node *node;
+       void *ret;
+
+       hash = ht->hash_fct(key);
+
+       rcu_read_lock();
+       node = rcu_dereference(ht->tbl[hash]);
+       for (;;) {
+               if (likely(!node)) {
+                       ret = NULL;
+                       break;
+               }
+               if (node->key == key) {
+                       ret = node->data;
+                       break;
+               }
+               node = rcu_dereference(node->next);
+       }
+       rcu_read_unlock();
+
+       return ret;
+}
+
+/*
+ * Will re-try until either:
+ * - The key is already there (-EEXIST)
+ * - We successfully add the key at the head of a table bucket.
+ */
+int ht_add(struct rcu_ht *ht, void *key, void *data)
+{
+       struct rcu_ht_node *node, *old_head, *new_head;
+       unsigned long hash;
+       int ret = 0;
+
+       new_head = calloc(1, sizeof(struct rcu_ht_node));
+       new_head->key = key;
+       new_head->data = data;
+       hash = ht->hash_fct(key);
+
+       /* here comes the fun and tricky part.
+        * Add at the beginning with a cmpxchg.
+        * Hold a read lock between the moment the first element is read
+        * and the nodes traversal (to find duplicates). This ensures
+        * the head pointer has not been reclaimed when cmpxchg is done.
+        * Always adding at the head ensures that we would have to
+        * re-try if a new item has been added concurrently. So we ensure that
+        * we never add duplicates. */
+retry:
+       rcu_read_lock();
+
+       old_head = node = rcu_dereference(ht->tbl[hash]);
+       for (;;) {
+               if (likely(!node)) {
+                       break;
+               }
+               if (node->key == key) {
+                       ret = -EEXIST;
+                       goto end;
+               }
+               node = rcu_dereference(node->next);
+       }
+       if (rcu_cmpxchg_pointer(&ht->tbl[hash], old_head, new_head) != old_head)
+               goto restart;
+end:
+       rcu_read_unlock();
+
+       return ret;
+
+       /* restart loop, release and re-take the read lock to be kind to GP */
+restart:
+       rcu_read_unlock();
+       goto retry;
+}
+
+/*
+ * Restart until we successfully remove the entry, or no entry is left
+ * ((void *)(unsigned long)-ENOENT).
+ */
+void *ht_steal(struct rcu_ht *ht, void *key)
+{
+       struct rcu_ht_node **prev, *node;
+       unsigned long hash;
+       void *data;
+
+       hash = ht->hash_fct(key);
+
+retry:
+       rcu_read_lock();
+
+       prev = &ht->tbl[hash];
+       node = rcu_dereference(*prev);
+       for (;;) {
+               if (likely(!node)) {
+                       data = (void *)(unsigned long)-ENOENT;
+                       goto end;
+               }
+               if (node->key == key) {
+                       break;
+               }
+               prev = &node->next;
+               node = rcu_dereference(*prev);
+       }
+       /* Found it ! pointer to object is in "prev" */
+       if (rcu_cmpxchg_pointer(prev, node, node->next) != node)
+               goto restart;
+end:
+       rcu_read_unlock();
+
+       data = node->data;
+       call_rcu(free, node);
+
+       return data;
+
+       /* restart loop, release and re-take the read lock to be kind to GP */
+restart:
+       rcu_read_unlock();
+       goto retry;
+}
+
+int ht_delete(struct rcu_ht *ht, void *key)
+{
+       void *data;
+
+       data = ht_steal(ht, key);
+       if (data) {
+               if (ht->free_fct && data)
+                       call_rcu(ht->free_fct, data);
+               return 0;
+       } else {
+               return -ENOENT;
+       }
+}
+
+unsigned long stupid_hash(void *key)
+{
+       return (unsigned long)key % HASH_SIZE;
+}
diff --git a/urcu-ht.h b/urcu-ht.h
new file mode 100644 (file)
index 0000000..0cbd1e6
--- /dev/null
+++ b/urcu-ht.h
@@ -0,0 +1,23 @@
+#ifndef _URCU_HT_H
+#define _URCU_HT_H
+
+#define HASH_SIZE      4096
+typedef unsigned long (*ht_hash_fct)(void *key);
+
+struct rcu_ht *ht_new(ht_hash_fct hash_fct, void (*free_fct)(void *data));
+
+void ht_delete_all(struct rcu_ht *ht);
+
+void ht_destroy(struct rcu_ht *ht);
+
+void *ht_lookup(struct rcu_ht *ht, void *key);
+
+int ht_add(struct rcu_ht *ht, void *key, void *data);
+
+int ht_delete(struct rcu_ht *ht, void *key);
+
+void *ht_steal(struct rcu_ht *ht, void *key);
+
+unsigned long stupid_hash(void *key);
+
+#endif /* _URCU_HT_H */
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