Changeset ea7890e7 in mainline for kernel/generic/src/proc/thread.c

Timestamp:

2007-06-01T15:47:46Z (18 years ago)

Author:

Jakub Jermar <jakub@…>

Branches:

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

Children:

07be3c4

Parents:

ff3a34b

Message:

More efficient and simpler task termination.

Based on the assumption, that after its creation, only the task itself can create more threads for itself,
the last thread with userspace context to execute thread_exit() will perform futex and IPC cleanup. When
the task has no threads, it is destroyed. Both the cleanup and destruction is controlled by reference
counting.

As for userspace threads, even though there could be a global garbage collector for joining threads, it is
much simpler if the uinit thread detaches itself before switching to userspace.

task_kill() is now an idempotent operation. It just instructs the threads within a task to exit.

Change in the name of a thread state: Undead → JoinMe.

File:

• kernel/generic/src/proc/thread.c (modified) (13 diffs)

kernel/generic/src/proc/thread.c

@@ -68 +68 @@
 #include <syscall/copy.h>
 #include <errno.h>
+#include <console/klog.h>
 
 
@@ -78 +79 @@
         "Entering",
         "Exiting",
-        "Undead"
+        "JoinMe"
 }; 
 
@@ -329 +330 @@
 
         t->interrupted = false; 
-        t->join_type = None;
         t->detached = false;
         waitq_initialize(&t->join_wq);
@@ -343 +343 @@
         thread_create_arch(t);  
 
-        ipl = interrupts_disable();      
-        spinlock_lock(&task->lock);
-        if (!task->accept_new_threads) {
-                spinlock_unlock(&task->lock);
-                slab_free(thread_slab, t);
-                interrupts_restore(ipl);
-                return NULL;
-        } else {
-                /*
-                 * Bump the reference count so that this task cannot be
-                 * destroyed while the new thread is being attached to it.
-                 */
-                task->refcount++;
-        }
-        spinlock_unlock(&task->lock);
-        interrupts_restore(ipl);
-
         if (!(flags & THREAD_FLAG_NOATTACH))
                 thread_attach(t, task);
@@ -374 +357 @@
 void thread_destroy(thread_t *t)
 {
-        bool destroy_task = false;
-
-        ASSERT(t->state == Exiting || t->state == Undead);
+        ASSERT(t->state == Exiting || t->state == JoinMe);
         ASSERT(t->task);
         ASSERT(t->cpu);
@@ -396 +377 @@
         spinlock_lock(&t->task->lock);
         list_remove(&t->th_link);
-        if (--t->task->refcount == 0) {
-                t->task->accept_new_threads = false;
-                destroy_task = true;
-        }
         spinlock_unlock(&t->task->lock);        
-        
-        if (destroy_task)
+
+        /*
+         * t is guaranteed to be the very last thread of its task.
+         * It is safe to destroy the task.
+         */
+        if (atomic_predec(&t->task->refcount) == 0)
                 task_destroy(t->task);
         
@@ -432 +413 @@
          * Attach to the current task.
          */
-        ipl = interrupts_disable();      
+        ipl = interrupts_disable();
         spinlock_lock(&task->lock);
-        ASSERT(task->refcount);
+        atomic_inc(&task->refcount);
+        atomic_inc(&task->lifecount);
         list_append(&t->th_link, &task->th_head);
-        if (task->refcount == 1)
-                task->main_thread = t;
         spinlock_unlock(&task->lock);
 
@@ -459 +439 @@
 {
         ipl_t ipl;
+
+        if (atomic_predec(&TASK->lifecount) == 0) {
+                /*
+                 * We are the last thread in the task that still has not exited.
+                 * With the exception of the moment the task was created, new
+                 * threads can only be created by threads of the same task.
+                 * We are safe to perform cleanup.
+                 */
+                if (THREAD->flags & THREAD_FLAG_USPACE) {
+                        ipc_cleanup();
+                        futex_cleanup();
+                        klog_printf("Cleanup of task %llu completed.",
+                            TASK->taskid);
+                }
+        }
 
 restart:
@@ -469 +464 @@
                 goto restart;
         }
+        
         THREAD->state = Exiting;
         spinlock_unlock(&THREAD->lock);
@@ -525 +521 @@
 /** Detach thread.
  *
- * Mark the thread as detached, if the thread is already in the Undead state,
+ * Mark the thread as detached, if the thread is already in the JoinMe state,
  * deallocate its resources.
  *
@@ -541 +537 @@
         spinlock_lock(&t->lock);
         ASSERT(!t->detached);
-        if (t->state == Undead) {
+        if (t->state == JoinMe) {
                 thread_destroy(t);      /* unlocks &t->lock */
                 interrupts_restore(ipl);
@@ -703 +699 @@
                             sizeof(t->tid));
                         if (rc != 0) {
-                                ipl_t ipl;
-
                                 /*
                                  * We have encountered a failure, but the thread
@@ -712 +706 @@
 
                                 /*
-                                 * The new thread structure is initialized,
-                                 * but is still not visible to the system.
+                                 * The new thread structure is initialized, but
+                                 * is still not visible to the system.
                                  * We can safely deallocate it.
                                  */
                                 slab_free(thread_slab, t);
                                 free(kernel_uarg);
-
-                                /*
-                                 * Now we need to decrement the task reference
-                                 * counter. Because we are running within the
-                                 * same task, thread t is not the last thread
-                                 * in the task, so it is safe to merely
-                                 * decrement the counter.
-                                 */
-                                ipl = interrupts_disable();
-                                spinlock_lock(&TASK->lock);
-                                TASK->refcount--;
-                                spinlock_unlock(&TASK->lock);
-                                interrupts_restore(ipl);
 
                                 return (unative_t) rc;