Changes in / [b8d6783:f76696f] in mainline

Location:

uspace

Files:

• app/tester/Makefile (modified) (1 diff)
• app/tester/ipc/starve.c (added)
• app/tester/ipc/starve.def (added)
• app/tester/tester.c (modified) (1 diff)
• app/tester/tester.h (modified) (1 diff)
• lib/c/generic/async.c (modified) (5 diffs)

uspace/app/tester/Makefile

@@ -50 +50 @@
         vfs/vfs1.c \
         ipc/ping_pong.c \
+        ipc/starve.c \
         loop/loop1.c \
         mm/common.c \

uspace/app/tester/tester.c

@@ -60 +60 @@
 #include "vfs/vfs1.def"
 #include "ipc/ping_pong.def"
+#include "ipc/starve.def"
 #include "loop/loop1.def"
 #include "mm/malloc1.def"

uspace/app/tester/tester.h

@@ -93 +93 @@
 extern const char *test_vfs1(void);
 extern const char *test_ping_pong(void);
+extern const char *test_starve_ipc(void);
 extern const char *test_loop1(void);
 extern const char *test_malloc1(void);

uspace/lib/c/generic/async.c

@@ -249 +249 @@
 static void to_event_initialize(to_event_t *to)
 {
-        struct timeval tv = { 0 };
+        struct timeval tv = { 0, 0 };
 
         to->inlist = false;
@@ -1017 +1017 @@
                 
                 suseconds_t timeout;
+                unsigned int flags = SYNCH_FLAGS_NONE;
                 if (!list_empty(&timeout_list)) {
                         awaiter_t *waiter = list_get_instance(
@@ -1027 +1028 @@
                                 futex_up(&async_futex);
                                 handle_expired_timeouts();
-                                continue;
-                        } else
+                                /*
+                                 * Notice that even if the event(s) already
+                                 * expired (and thus the other fibril was
+                                 * supposed to be running already),
+                                 * we check for incoming IPC.
+                                 *
+                                 * Otherwise, a fibril that continuously
+                                 * creates (almost) expired events could
+                                 * prevent IPC retrieval from the kernel.
+                                 */
+                                timeout = 0;
+                                flags = SYNCH_FLAGS_NON_BLOCKING;
+
+                        } else {
                                 timeout = tv_sub(&waiter->to_event.expires, &tv);
-                } else
+                                futex_up(&async_futex);
+                        }
+                } else {
+                        futex_up(&async_futex);
                         timeout = SYNCH_NO_TIMEOUT;
-                
-                futex_up(&async_futex);
+                }
                 
                 atomic_inc(&threads_in_ipc_wait);
                 
                 ipc_call_t call;
-                ipc_callid_t callid = ipc_wait_cycle(&call, timeout,
-                    SYNCH_FLAGS_NONE);
+                ipc_callid_t callid = ipc_wait_cycle(&call, timeout, flags);
                 
                 atomic_dec(&threads_in_ipc_wait);
@@ -1298 +1312 @@
         
         amsg_t *msg = (amsg_t *) amsgid;
-        
-        /* TODO: Let it go through the event read at least once */
-        if (timeout < 0)
-                return ETIMEOUT;
-        
+
         futex_down(&async_futex);
 
@@ -1313 +1323 @@
         }
         
+        /*
+         * Negative timeout is converted to zero timeout to avoid
+         * using tv_add with negative augmenter.
+         */
+        if (timeout < 0)
+                timeout = 0;
+
         gettimeofday(&msg->wdata.to_event.expires, NULL);
         tv_add(&msg->wdata.to_event.expires, timeout);
         
+        /*
+         * Current fibril is inserted as waiting regardless of the
+         * "size" of the timeout.
+         *
+         * Checking for msg->done and immediately bailing out when
+         * timeout == 0 would mean that the manager fibril would never
+         * run (consider single threaded program).
+         * Thus the IPC answer would be never retrieved from the kernel.
+         *
+         * Notice that the actual delay would be very small because we
+         * - switch to manager fibril
+         * - the manager sees expired timeout
+         * - and thus adds us back to ready queue
+         * - manager switches back to some ready fibril
+         *   (prior it, it checks for incoming IPC).
+         *
+         */
         msg->wdata.fid = fibril_get_id();
         msg->wdata.active = false;