init version
authorMathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Fri, 6 Feb 2009 00:06:44 +0000 (19:06 -0500)
committerMathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Fri, 6 Feb 2009 00:06:44 +0000 (19:06 -0500)
Makefile [new file with mode: 0644]
urcu.c [new file with mode: 0644]
urcu.h [new file with mode: 0644]

diff --git a/Makefile b/Makefile
new file mode 100644 (file)
index 0000000..1f53f00
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,6 @@
+
+test_urcu: urcu.o test_urcu.c
+       gcc -g -o test_urcu urcu.o test_urcu.c
+
+urcu.o: urcu.c urcu.h
+       gcc -g -o urcu.o urcu.c
diff --git a/urcu.c b/urcu.c
new file mode 100644 (file)
index 0000000..b8c80ab
--- /dev/null
+++ b/urcu.c
@@ -0,0 +1,250 @@
+#include <stdio.h>
+#include <pthread.h>
+#include <signal.h>
+#include <assert.h>
+
+#include "urcu.h"
+
+pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
+
+/* Global quiescent period parity */
+int urcu_qparity;
+
+int __thread urcu_active_readers[2];
+
+/* Thread IDs of registered readers */
+#define INIT_NUM_THREADS 4
+
+struct reader_data {
+       pthread_t tid;
+       int **urcu_active_readers;
+};
+
+static struct reader_data *reader_data;
+static int num_readers, alloc_readers;
+static int sig_done;
+
+/*
+ * called with urcu_mutex held.
+ */
+static int switch_next_urcu_qparity(void)
+{
+       int old_parity = urcu_qparity;
+       urcu_qparity = 1 - old_parity;
+       return old_parity;
+}
+
+static void force_mb_all_threads(void)
+{
+       pthread_t *index;
+       /*
+        * Ask for each threads to execute a mb() so we can consider the
+        * compiler barriers around rcu read lock as real memory barriers.
+        */
+       if (!reader_data)
+               return;
+       sigtask = TASK_FORCE_MB;
+       sig_done = 0;
+       mb();   /* write sig_done and sigtask before sending the signals */
+       for (index = reader_data; index < reader_data + num_readers; index++)
+               pthread_kill(*index, SIGURCU);
+       /*
+        * Wait for sighandler (and thus mb()) to execute on every thread.
+        * BUSY-LOOP.
+        */
+       while (sig_done < num_readers)
+               barrier();
+       mb();   /* read sig_done before writing sigtask */
+       sigtask = TASK_NONE;
+}
+
+void wait_for_quiescent_state(int parity)
+{
+
+       if (!reader_data)
+               return;
+       /* Wait for each thread urcu_active_readers count to become 0.
+        */
+       for (index = readers_data; index < reader_data + num_readers; index++) {
+               /*
+                * BUSY-LOOP.
+                */
+               while (*index->urcu_active_readers != 0)
+                       barrier();
+       }
+       /*
+        * Locally : read *index->urcu_active_readers before freeing old
+        * pointer.
+        * Remote (reader threads) : Order urcu_qparity update and other
+        * thread's quiescent state counter read.
+        */
+       force_mb_all_threads();
+}
+
+/*
+ * Return old pointer, OK to free, no more reference exist.
+ */
+void *urcu_publish_content(void **ptr, void *new)
+{
+       int ret, prev_parity;
+       void *oldptr;
+
+       ret = pthread_mutex_lock(&urcu_mutex);
+       if (ret) {
+               perror("Error in %s pthread mutex lock", __func__);
+               exit(-1);
+       }
+
+       /*
+        * We can publish the new pointer before we change the current qparity.
+        * Readers seeing the new pointer while being in the previous qparity
+        * window will make us wait until the end of the quiescent state before
+        * we release the unrelated memory area. However, given we hold the
+        * urcu_mutex, we are making sure that no further garbage collection can
+        * occur until we release the mutex, therefore we guarantee that this
+        * given reader will have completed its execution using the new pointer
+        * when the next quiescent state window will be over.
+        */
+       oldptr = *ptr;
+       *ptr = new;
+       wmb();          /* Write ptr before changing the qparity */
+       /* All threads should read qparity before ptr */
+       force_rmb_all_threads();
+       prev_parity = switch_next_urcu_qparity();
+
+       /*
+        * Wait for previous parity to be empty of readers.
+        */
+       wait_for_quiescent_state(prev_parity);
+       /*
+        * Deleting old data is ok !
+        */
+       
+       ret = pthread_mutex_unlock(&urcu_mutex);
+       if (ret) {
+               perror("Error in %s pthread mutex lock", __func__);
+               exit(-1);
+       }
+       return oldptr;
+}
+
+void urcu_add_reader(pthread_t id)
+{
+       if (!reader_data) {
+               alloc_readers = INIT_NUM_THREADS;
+               num_readers = 1;
+               reader_data =
+                       malloc(sizeof(struct reader_data) * alloc_readers);
+               return;
+       }
+       if (alloc_readers < num_readers + 1) {
+               pthread_t *oldarray;
+               oldarray = reader_data;
+               reader_data = malloc(sizeof(struct reader_data)
+                               * (alloc_readers << 1));
+               memcpy(reader_data, oldarray,
+                       sizeof(struct reader_data) * alloc_readers);
+               alloc_readers <<= 1;
+               free(oldarray);
+       }
+       reader_data[num_readers].tid = id;
+       /* reference to the TLS of _this_ reader thread. */
+       reader_data[num_readers].urcu_active_readers = urcu_active_readers;
+       num_readers++;
+}
+
+/*
+ * Never shrink (implementation limitation).
+ * This is O(nb threads). Eventually use a hash table.
+ */
+void urcu_remove_reader(pthread_t id)
+{
+       struct reader_data *index;
+
+       assert(reader_data != NULL);
+       for (index = reader_data; index < reader_data + num_readers; index++) {
+               if (index->tid == id) {
+                       memcpy(index, &reader_data[num_readers - 1],
+                               sizeof(struct reader_data));
+                       reader_data[num_readers - 1].tid = 0;
+                       reader_data[num_readers - 1].urcu_active_readers = NULL;
+                       num_readers--;
+                       return;
+               }
+       }
+       /* Hrm not found, forgot to register ? */
+       assert(0);
+}
+
+void urcu_register_thread(void)
+{
+       pthread_t self = pthread_self();
+
+       ret = pthread_mutex_lock(&urcu_mutex);
+       if (ret) {
+               perror("Error in %s pthread mutex lock", __func__);
+               exit(-1);
+       }
+
+       urcu_add_reader(self);
+
+
+       ret = pthread_mutex_unlock(&urcu_mutex);
+       if (ret) {
+               perror("Error in %s pthread mutex unlock", __func__);
+               exit(-1);
+       }
+}
+
+void urcu_register_thread(void)
+{
+       pthread_t self = pthread_self();
+
+       ret = pthread_mutex_lock(&urcu_mutex);
+       if (ret) {
+               perror("Error in %s pthread mutex lock", __func__);
+               exit(-1);
+       }
+
+       urcu_remove_reader(self);
+
+       ret = pthread_mutex_unlock(&urcu_mutex);
+       if (ret) {
+               perror("Error in %s pthread mutex unlock", __func__);
+               exit(-1);
+       }
+
+}
+
+void handler(int signo, siginfo_t *siginfo, void *context)
+{
+       mb();
+       atomic_inc(&sig_done);
+}
+
+void __attribute__((constructor)) urcu_init(void)
+{
+       struct sigaction act;
+       int ret;
+
+       act.sa_sigaction = sigurcu_handler;
+       ret = sigaction(SIGURCU, &act, NULL);
+       if (!ret) {
+               perror("Error in %s sigaction", __func__);
+               exit(-1);
+       }
+}
+
+void __attribute__((destructor)) urcu_exit(void)
+{
+       struct sigaction act;
+       int ret;
+
+       ret = sigaction(SIGURCU, NULL, &act);
+       if (!ret) {
+               perror("Error in %s sigaction", __func__);
+               exit(-1);
+       }
+       assert(act.sa_sigaction == sigurcu_handler);
+       free(reader_data);
+}
diff --git a/urcu.h b/urcu.h
new file mode 100644 (file)
index 0000000..d417f34
--- /dev/null
+++ b/urcu.h
@@ -0,0 +1,69 @@
+#ifndef _URCU_H
+#define _URCU_H
+
+/* The "volatile" is due to gcc bugs */
+#define barrier() __asm__ __volatile__("": : :"memory")
+
+/* x86 32/64 specific */
+#define mb()    asm volatile("mfence":::"memory")
+#define rmb()   asm volatile("lfence":::"memory")
+#define wmb()   asm volatile("sfence" ::: "memory")
+
+
+
+/* x86 32 */
+static inline void atomic_inc(int *v)
+{
+       asm volatile("lock; incl %0"
+                    : "+m" (v->counter));
+}
+
+/* Nop everywhere except on alpha. */
+#define smp_read_barrier_depends()
+
+#define SIGURCU SIGUSR1
+
+/* Global quiescent period parity */
+extern int urcu_qparity;
+
+extern int __thread urcu_active_readers[2];
+
+static inline int get_urcu_qparity(void)
+{
+       return urcu_qparity;
+}
+
+/*
+ * returns urcu_parity.
+ */
+static inline int rcu_read_lock(void)
+{
+       int urcu_parity = get_urcu_qparity();
+       urcu_active_readers[urcu_parity]++;
+       /*
+        * Increment active readers count before accessing the pointer.
+        * See force_mb_all_threads().
+        */
+       barrier();
+       return urcu_parity;
+}
+
+static inline void rcu_read_unlock(int urcu_parity)
+{
+       barrier();
+       /*
+        * Finish using rcu before decrementing the pointer.
+        * See force_mb_all_threads().
+        */
+       urcu_active_readers[urcu_parity]--;
+}
+
+extern void *urcu_publish_content(void **ptr, void *new);
+
+/*
+ * Reader thread registration.
+ */
+extern void urcu_register_thread(void);
+extern void urcu_register_thread(void);
+
+#endif /* _URCU_H */
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