Changeset 4fded58 in mainline for generic/src/synch/futex.c

Timestamp:

2006-05-31T12:33:30Z (19 years ago)

Author:

Jakub Jermar <jakub@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

76d7305

Parents:

3de6dd7a

Message:

Reference counting for futexes.

File:

• generic/src/synch/futex.c (modified) (9 diffs)

generic/src/synch/futex.c

@@ -30 +30 @@
  * @file        futex.c
  * @brief       Kernel backend for futexes.
- *
- * @todo Deallocation of orphaned kernel-side futex structures is not currently implemented.
  */
 
@@ -42 +40 @@
 #include <mm/slab.h>
 #include <proc/thread.h>
+#include <proc/task.h>
 #include <genarch/mm/page_pt.h>
 #include <genarch/mm/page_ht.h>
@@ -61 +60 @@
 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;
 
@@ -90 +93 @@
         link_initialize(&futex->ht_link);
         futex->paddr = 0;
+        futex->refcount = 1;
 }
 
@@ -169 +173 @@
 /** 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.
@@ -179 +183 @@
         link_t *item;
         futex_t *futex;
+        btree_node_t *leaf;
         
         /*
@@ -188 +193 @@
         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,
@@ -205 +227 @@
                 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 {
@@ -211 +249 @@
                         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);
                 }