WebSVN – HelenOS-historic – Diff – /kernel/trunk/generic/src/synch/futex.c

  */
 /**
  * @file    futex.c
  * @brief   Kernel backend for futexes.
- *
- * @todo Deallocation of orphaned kernel-side futex structures is not currently implemented.
  */
 #include <synch/futex.h>
 #include <synch/rwlock.h>
 #include <synch/spinlock.h>
 #include <synch/synch.h>
 #include <mm/frame.h>
 #include <mm/page.h>
 #include <mm/slab.h>
 #include <proc/thread.h>
+#include <proc/task.h>
 #include <genarch/mm/page_pt.h>
 #include <genarch/mm/page_ht.h>
 #include <adt/hash_table.h>
 #include <adt/list.h>
 #include <arch.h>
 static futex_t *futex_find(__address paddr);
 static index_t futex_ht_hash(__native *key);
 static bool futex_ht_compare(__native *key, count_t keys, link_t *item);
 static void futex_ht_remove_callback(link_t *item);
+/**
-/** Read-write lock protecting global futex hash table. */
+ * Read-write lock protecting global futex hash table.
+ * It is also used to serialize access to all futex_t structures.
+ * Must be acquired before the task futex B+tree lock.
+ */
 static rwlock_t futex_ht_lock;
 /** Futex hash table. */
 static hash_table_t futex_ht;
 void futex_initialize(futex_t *futex)
+{
     waitq_initialize(&futex->wq);
     link_initialize(&futex->ht_link);
     futex->paddr = 0;
+    futex->refcount = 1;
+}
 /** Sleep in futex wait queue.
+ *
  * @param uaddr Userspace address of the futex counter.
     return 0;
+}
 /** Find kernel address of the futex structure corresponding to paddr.
+ *
- * If the structure does not exist alreay, a new one is created.
+ * If the structure does not exist already, a new one is created.
+ *
  * @param paddr Physical address of the userspace futex counter.
+ *
  * @return Address of the kernel futex structure.
  */
 futex_t *futex_find(__address paddr)
+{
     link_t *item;
     futex_t *futex;
+    btree_node_t *leaf;
     /*
      * Find the respective futex structure
      * or allocate new one if it does not exist already.
      */
     rwlock_read_lock(&futex_ht_lock);
     item = hash_table_find(&futex_ht, &paddr);
     if (item) {
         futex = hash_table_get_instance(item, futex_t, ht_link);
+        /*
+         * See if the current task knows this futex.
+         */
+        mutex_lock(&TASK->futexes_lock);
+        if (!btree_search(&TASK->futexes, paddr, &leaf)) {
+            /*
+             * The futex is new to the current task.
+             * However, we only have read access.
+             * Gain write access and try again.
+             */
+            mutex_unlock(&TASK->futexes_lock);
+            goto gain_write_access;
+        }
+        mutex_unlock(&TASK->futexes_lock);
         rwlock_read_unlock(&futex_ht_lock);
     } else {
+gain_write_access:
         /*
          * Upgrade to writer is not currently supported,
          * therefore, it is necessary to release the read lock
          * and reacquire it as a writer.
          */
          * the hash table once again with write access.
          */
         item = hash_table_find(&futex_ht, &paddr);
         if (item) {
             futex = hash_table_get_instance(item, futex_t, ht_link);
+            /*
+             * See if this futex is known to the current task.
+             */
+            mutex_lock(&TASK->futexes_lock);
+            if (!btree_search(&TASK->futexes, paddr, &leaf)) {
+                /*
+                 * The futex is new to the current task.
+                 * Upgrade its reference count and put it to the
+                 * current task's B+tree of known futexes.
+                 */
+                futex->refcount++;
+                btree_insert(&TASK->futexes, paddr, futex, leaf);
+            }
+            mutex_unlock(&TASK->futexes_lock);
             rwlock_write_unlock(&futex_ht_lock);
         } else {
             futex = (futex_t *) malloc(sizeof(futex_t), 0);
             futex_initialize(futex);
             futex->paddr = paddr;
             hash_table_insert(&futex_ht, &paddr, &futex->ht_link);
+            /*
+             * This is the first task referencing the futex.
+             * It can be directly inserted into its
+             * B+tree of known futexes.
+             */
+            mutex_lock(&TASK->futexes_lock);
+            btree_insert(&TASK->futexes, paddr, futex, NULL);
+            mutex_unlock(&TASK->futexes_lock);
             rwlock_write_unlock(&futex_ht_lock);
+        }
+    }
     return futex;

Subversion Repositories HelenOS-historic

(root)/kernel/trunk/generic/src/synch/futex.c – Rev 1414 → 1460