X-Git-Url: https://pd.if.org/git/?p=nbds;a=blobdiff_plain;f=runtime%2Frcu.c;fp=runtime%2Frcu.c;h=dfa49c8652ed277de7eb847716bd61d0f21e96a5;hp=0000000000000000000000000000000000000000;hb=efd90a1b8a9d3bbb1bdd8e6ae41b3462e7193fb2;hpb=69f813b01bb0472f9ec5368b26a702bcc06f7e29

diff --git a/runtime/rcu.c b/runtime/rcu.c
new file mode 100644
index 0000000..dfa49c8
--- /dev/null
+++ b/runtime/rcu.c
@@ -0,0 +1,211 @@
+/* 
+ * Written by Josh Dybnis and released to the public domain, as explained at
+ * http://creativecommons.org/licenses/publicdomain
+ *
+ * safe memory reclemation using a simple technique from rcu
+ */
+#include <string.h>
+#include "common.h"
+#include "rcu.h"
+#include "lwt.h"
+#include "mem.h"
+#include "nbd.h"
+#include "tls.h"
+
+#define RCU_POST_THRESHOLD 10
+#define RCU_QUEUE_SCALE 20
+
+typedef struct fifo {
+    uint32_t head;
+    uint32_t tail;
+    uint32_t scale;
+    void *x[0];
+} fifo_t;
+
+static uint64_t rcu_[MAX_NUM_THREADS][MAX_NUM_THREADS] = {};
+static uint64_t rcu_last_posted_[MAX_NUM_THREADS][MAX_NUM_THREADS] = {};
+static fifo_t *pending_[MAX_NUM_THREADS] = {};
+static int num_threads_ = 0;
+
+static fifo_t *fifo_alloc(int scale) {
+    fifo_t *q = (fifo_t *)nbd_malloc(sizeof(fifo_t) + (1 << scale) * sizeof(void *)); 
+    memset(q, 0, sizeof(fifo_t));
+    q->scale = scale;
+    q->head = 0;
+    q->tail = 0;
+    return q;
+}
+
+static uint32_t fifo_index (fifo_t *q, uint32_t i) {
+    return i & MASK(q->scale);
+}
+
+static void fifo_enqueue (fifo_t *q, void *x) {
+    assert(fifo_index(q, q->head + 1) != fifo_index(q, q->tail));
+    uint32_t i = fifo_index(q, q->head++);
+    q->x[i] = x;
+}
+
+static void *fifo_dequeue (fifo_t *q) {
+    uint32_t i = fifo_index(q, q->tail++);
+    return q->x[i];
+}
+
+void rcu_thread_init (int id) {
+    assert(id < MAX_NUM_THREADS);
+    if (pending_[id] == NULL) {
+        pending_[id] = fifo_alloc(RCU_QUEUE_SCALE);
+        SYNC_ADD(&num_threads_, 1);
+    }
+}
+
+static void rcu_post (uint64_t x) {
+    LOCALIZE_THREAD_LOCAL(tid_, int);
+    if (x - rcu_last_posted_[tid_][tid_] < RCU_POST_THRESHOLD)
+        return;
+
+    int next_thread_id = (tid_ + 1) % num_threads_;
+
+    TRACE("r0", "rcu_post: %llu", x, 0);
+    rcu_[next_thread_id][tid_] = rcu_last_posted_[tid_][tid_] = x;
+}
+
+void rcu_update (void) {
+    LOCALIZE_THREAD_LOCAL(tid_, int);
+    assert(tid_ < num_threads_);
+    int next_thread_id = (tid_ + 1) % num_threads_;
+    int i;
+    for (i = 0; i < num_threads_; ++i) {
+        if (i == tid_)
+            continue;
+
+        // No need to post an update if the value hasn't changed
+        if (rcu_[tid_][i] == rcu_last_posted_[tid_][i])
+            continue;
+
+        uint64_t x = rcu_[tid_][i];
+        rcu_[next_thread_id][i] = rcu_last_posted_[tid_][i] = x;
+    }
+
+    // free
+    while (pending_[tid_]->tail != rcu_[tid_][tid_]) {
+        nbd_free(fifo_dequeue(pending_[tid_]));
+    }
+}
+
+void nbd_defer_free (void *x) {
+    LOCALIZE_THREAD_LOCAL(tid_, int);
+    fifo_enqueue(pending_[tid_], x);
+    TRACE("r0", "nbd_defer_free: put %p on queue at position %llu", x, pending_[tid_]->head);
+    rcu_post(pending_[tid_]->head);
+}
+
+#ifdef MAKE_rcu_test
+#include <pthread.h>
+#include <errno.h>
+#include <stdio.h>
+
+#define NUM_ITERATIONS 10000000
+
+typedef struct node {
+    struct node *next;
+} node_t;
+
+typedef struct lifo {
+    node_t *head;
+} lifo_t;
+
+static volatile int wait_;
+static lifo_t *stk_;
+
+static lifo_t *lifo_alloc (void) {
+    lifo_t *stk = (lifo_t *)nbd_malloc(sizeof(lifo_t)); 
+    memset(stk, 0, sizeof(lifo_t));
+    return stk;
+}
+
+static void lifo_aba_push (lifo_t *stk, node_t *x) {
+    node_t *head;
+    do {
+        head = ((volatile lifo_t *)stk)->head;
+        ((volatile node_t *)x)->next = head;
+    } while (__sync_val_compare_and_swap(&stk->head, head, x) != head);
+}
+
+node_t *lifo_aba_pop (lifo_t *stk) {
+    node_t *head;
+    do {
+        head = ((volatile lifo_t *)stk)->head;
+        if (head == NULL)
+            return NULL;
+    } while (__sync_val_compare_and_swap(&stk->head, head, head->next) != head);
+    head->next = NULL;
+    return head;
+}
+
+node_t *node_alloc (void) {
+    node_t *node = (node_t *)nbd_malloc(sizeof(node_t));
+    memset(node, 0, sizeof(node_t));
+    return node;
+}
+
+void *worker (void *arg) {
+    int id = (int)(size_t)arg;
+    unsigned int rand_seed = (unsigned int)id + 1;
+    nbd_thread_init(id);
+
+    // Wait for all the worker threads to be ready.
+    __sync_fetch_and_add(&wait_, -1);
+    do {} while (wait_); 
+
+    int i;
+    for (i = 0; i < NUM_ITERATIONS; ++ i) {
+        int n = rand_r(&rand_seed);
+        if (n & 0x1) {
+            lifo_aba_push(stk_, node_alloc());
+        } else {
+            node_t *x = lifo_aba_pop(stk_);
+            if (x) {
+                nbd_defer_free(x);
+            }
+        }
+        rcu_update();
+    }
+
+    return NULL;
+}
+
+int main (int argc, char **argv) {
+    nbd_init();
+    //lwt_set_trace_level("m0r0");
+
+    int num_threads = 2;
+    if (argc == 2)
+    {
+        errno = 0;
+        num_threads = strtol(argv[1], NULL, 10);
+        if (errno) {
+            fprintf(stderr, "%s: Invalid argument for number of threads\n", argv[0]);
+            return -1;
+        }
+        if (num_threads <= 0) {
+            fprintf(stderr, "%s: Number of threads must be at least 1\n", argv[0]);
+            return -1;
+        }
+    }
+
+    stk_ = lifo_alloc();
+    wait_ = num_threads;
+
+    pthread_t thread[num_threads];
+    for (int i = 0; i < num_threads; ++i) {
+        int rc = pthread_create(thread + i, NULL, worker, (void *)(size_t)i);
+        if (rc != 0) { perror("pthread_create"); return rc; }
+    }
+    for (int i = 0; i < num_threads; ++i) {
+        pthread_join(thread[i], NULL);
+    }
+
+    return 0;
+}
+#endif//rcu_test