Changes in uspace/lib/c/generic/fibril.c [4d11204:c170438] in mainline

File:

• uspace/lib/c/generic/fibril.c (modified) (13 diffs)

uspace/lib/c/generic/fibril.c

@@ -49 +49 @@
 #include <assert.h>
 #include <async.h>
-#include <futex.h>
 
 #ifdef FUTEX_UPGRADABLE
@@ -57 +56 @@
 /**
  * This futex serializes access to ready_list,
- * serialized_list, manager_list and fibril_list.
+ * manager_list and fibril_list.
  */
 static futex_t fibril_futex = FUTEX_INITIALIZER;
 
 static LIST_INITIALIZE(ready_list);
-static LIST_INITIALIZE(serialized_list);
 static LIST_INITIALIZE(manager_list);
 static LIST_INITIALIZE(fibril_list);
-
-/** Number of threads that are executing a manager fibril. */
-static int threads_in_manager;
-
-/**
- * Number of threads that are executing a manager fibril
- * and are serialized. Protected by async_futex.
- */
-static int serialized_threads;
-
-/** Fibril-local count of serialization. If > 0, we must not preempt */
-static fibril_local int serialization_count;
 
 /** Function that spans the whole life-cycle of a fibril.
@@ -96 +82 @@
         fibril->retval = fibril->func(fibril->arg);
         
+        futex_down(&async_futex);
         fibril_switch(FIBRIL_FROM_DEAD);
         /* Not reached */
@@ -127 +114 @@
         fibril->waits_for = NULL;
 
-        futex_lock(&fibril_futex);
+        fibril->switches = 0;
+
+        /*
+         * We are called before __tcb_set(), so we need to use
+         * futex_down/up() instead of futex_lock/unlock() that
+         * may attempt to access TLS.
+         */
+        futex_down(&fibril_futex);
         list_append(&fibril->all_link, &fibril_list);
-        futex_unlock(&fibril_futex);
+        futex_up(&fibril_futex);
         
         return fibril;
@@ -147 +141 @@
 /** Switch from the current fibril.
  *
- * If calling with FIBRIL_TO_MANAGER parameter, the async_futex should be
- * held.
+ * If stype is FIBRIL_TO_MANAGER or FIBRIL_FROM_DEAD, the async_futex must
+ * be held.
  *
  * @param stype Switch type. One of FIBRIL_PREEMPT, FIBRIL_TO_MANAGER,
@@ -160 +154 @@
 int fibril_switch(fibril_switch_type_t stype)
 {
-        int retval = 0;
-        
         futex_lock(&fibril_futex);
-        
-        if (stype == FIBRIL_PREEMPT && list_empty(&ready_list))
-                goto ret_0;
-        
-        if (stype == FIBRIL_FROM_MANAGER) {
-                if ((list_empty(&ready_list)) && (list_empty(&serialized_list)))
-                        goto ret_0;
-                
-                /*
-                 * Do not preempt if there is not enough threads to run the
-                 * ready fibrils which are not serialized.
-                 */
-                if ((list_empty(&serialized_list)) &&
-                    (threads_in_manager <= serialized_threads)) {
-                        goto ret_0;
+
+        switch (stype) {
+        case FIBRIL_PREEMPT:
+        case FIBRIL_FROM_MANAGER:
+                if (list_empty(&ready_list)) {
+                        futex_unlock(&fibril_futex);
+                        return 0;
                 }
-        }
-        
-        /* If we are going to manager and none exists, create it */
-        if ((stype == FIBRIL_TO_MANAGER) || (stype == FIBRIL_FROM_DEAD)) {
+                break;
+        case FIBRIL_TO_MANAGER:
+        case FIBRIL_FROM_DEAD:
+                /* Make sure the async_futex is held. */
+                assert((atomic_signed_t) async_futex.val.count <= 0);
+
+                /* If we are going to manager and none exists, create it */
                 while (list_empty(&manager_list)) {
                         futex_unlock(&fibril_futex);
@@ -188 +175 @@
                         futex_lock(&fibril_futex);
                 }
+                break;
         }
         
@@ -195 +183 @@
                 /* Save current state */
                 if (!context_save(&srcf->ctx)) {
-                        if (serialization_count)
-                                srcf->flags &= ~FIBRIL_SERIALIZED;
-                        
                         if (srcf->clean_after_me) {
                                 /*
@@ -222 +207 @@
                 }
                 
-                /* Save myself to the correct run list */
-                if (stype == FIBRIL_PREEMPT)
+                /* Put the current fibril into the correct run list */
+                switch (stype) {
+                case FIBRIL_PREEMPT:
                         list_append(&srcf->link, &ready_list);
-                else if (stype == FIBRIL_FROM_MANAGER) {
+                        break;
+                case FIBRIL_FROM_MANAGER:
                         list_append(&srcf->link, &manager_list);
-                        threads_in_manager--;
-                } else {
+                        break;
+                default:
+                        assert(stype == FIBRIL_TO_MANAGER);
+
+                        srcf->switches++;
+
                         /*
-                         * If stype == FIBRIL_TO_MANAGER, don't put ourselves to
-                         * any list, we should already be somewhere, or we will
-                         * be lost.
+                         * Don't put the current fibril into any list, it should
+                         * already be somewhere, or it will be lost.
                          */
+                        break;
                 }
         }
         
+        fibril_t *dstf;
+
         /* Choose a new fibril to run */
-        fibril_t *dstf;
-        if ((stype == FIBRIL_TO_MANAGER) || (stype == FIBRIL_FROM_DEAD)) {
+        switch (stype) {
+        case FIBRIL_TO_MANAGER:
+        case FIBRIL_FROM_DEAD:
                 dstf = list_get_instance(list_first(&manager_list), fibril_t,
                     link);
-                if (serialization_count && stype == FIBRIL_TO_MANAGER) {
-                        serialized_threads++;
-                        srcf->flags |= FIBRIL_SERIALIZED;
-                }
-                threads_in_manager++;
                 
                 if (stype == FIBRIL_FROM_DEAD) 
                         dstf->clean_after_me = srcf;
-        } else {
-                if (!list_empty(&serialized_list)) {
-                        dstf = list_get_instance(list_first(&serialized_list),
-                            fibril_t, link);
-                        serialized_threads--;
-                } else {
-                        dstf = list_get_instance(list_first(&ready_list),
-                            fibril_t, link);
-                }
-        }
+                break;
+        default:
+                dstf = list_get_instance(list_first(&ready_list), fibril_t,
+                    link);
+                break;
+        }
+
         list_remove(&dstf->link);
         
@@ -272 +258 @@
         context_restore(&dstf->ctx);
         /* not reached */
-        
-ret_0:
-        futex_unlock(&fibril_futex);
-        return retval;
 }
 
@@ -342 +324 @@
         
         futex_lock(&fibril_futex);
-        
-        if ((fibril->flags & FIBRIL_SERIALIZED))
-                list_append(&fibril->link, &serialized_list);
-        else
-                list_append(&fibril->link, &ready_list);
-        
+        list_append(&fibril->link, &ready_list);
         futex_unlock(&fibril_futex);
 }
@@ -370 +347 @@
 {
         futex_lock(&fibril_futex);
-        
         if (!list_empty(&manager_list))
                 list_remove(list_first(&manager_list));
-        
         futex_unlock(&fibril_futex);
 }
@@ -387 +362 @@
 }
 
-/** Disable preemption
- *
- * If the fibril wants to send several message in a row and does not want to be
- * preempted, it should start async_serialize_start() in the beginning of
- * communication and async_serialize_end() in the end. If it is a true
- * multithreaded application, it should protect the communication channel by a
- * futex as well.
- *
- */
-void fibril_inc_sercount(void)
-{
-        serialization_count++;
-}
-
-/** Restore the preemption counter to the previous state. */
-void fibril_dec_sercount(void)
-{
-        serialization_count--;
-}
-
-int fibril_get_sercount(void)
-{
-        return serialization_count;
-}
-
 /** @}
  */