Changeset c124c985 in mainline

Timestamp:

2018-07-16T15:38:16Z (6 years ago)

Author:

Jiří Zárevúcky <jiri.zarevucky@…>

Branches:

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

Children:

38d8849

Parents:

c45dc5e1

git-author:

Jiří Zárevúcky <jiri.zarevucky@…> (2018-07-13 23:18:58)

git-committer:

Jiří Zárevúcky <jiri.zarevucky@…> (2018-07-16 15:38:16)

Message:

Add fibril_rmutex_t type and fibril multithreading enablement.

Location:

uspace/lib/c

Files:

• generic/fibril.c (modified) (1 diff)
• include/fibril.h (modified) (1 diff)
• include/fibril_synch.h (modified) (1 diff)

uspace/lib/c/generic/fibril.c

@@ -344 +344 @@
 }
 
+static void _runner_fn(void *arg)
+{
+        futex_lock(&async_futex);
+        (void) fibril_switch(FIBRIL_FROM_BLOCKED);
+        __builtin_unreachable();
+}
+
+/**
+ * Spawn a given number of runners (i.e. OS threads) immediately, and
+ * unconditionally. This is meant to be used for tests and debugging.
+ * Regular programs should just use `fibril_enable_multithreaded()`.
+ *
+ * @param n  Number of runners to spawn.
+ * @return   Number of runners successfully spawned.
+ */
+int fibril_test_spawn_runners(int n)
+{
+        errno_t rc;
+
+        for (int i = 0; i < n; i++) {
+                thread_id_t tid;
+                rc = thread_create(_runner_fn, NULL, "fibril runner", &tid);
+                if (rc != EOK)
+                        return i;
+                thread_detach(tid);
+        }
+
+        return n;
+}
+
+/**
+ * Opt-in to have more than one runner thread.
+ *
+ * Currently, a task only ever runs in one thread because multithreading
+ * might break some existing code.
+ *
+ * Eventually, the number of runner threads for a given task should become
+ * configurable in the environment and this function becomes no-op.
+ */
+void fibril_enable_multithreaded(void)
+{
+        // TODO: Implement better.
+        //       For now, 4 total runners is a sensible default.
+        fibril_test_spawn_runners(3);
+}
+
+/**
+ * Detach a fibril.
+ */
+void fibril_detach(fid_t f)
+{
+        // TODO: Currently all fibrils are detached by default, but they
+        //       won't always be. Code that explicitly spawns fibrils with
+        //       limited lifetime should call this function.
+}
+
 /** @}
  */

uspace/lib/c/include/fibril.h

@@ -61 +61 @@
 extern void fibril_sleep(unsigned int);
 
+extern void fibril_enable_multithreaded(void);
+extern int fibril_test_spawn_runners(int);
+
+extern void fibril_detach(fid_t fid);
+
 static inline fid_t fibril_create(errno_t (*func)(void *), void *arg)
 {

uspace/lib/c/include/fibril_synch.h

@@ -41 +41 @@
 #include <sys/time.h>
 #include <stdbool.h>
+#include <futex.h>
+
+/**
+ * "Restricted" fibril mutex.
+ *
+ * Similar to `fibril_mutex_t`, but has a set of restrictions placed on its
+ * use. Within a rmutex critical section, you
+ *         - may not use any other synchronization primitive,
+ *           save for another `fibril_rmutex_t`. This includes nonblocking
+ *           operations like cvar signal and mutex unlock.
+ *         - may not read IPC messages
+ *         - may not start a new thread/fibril
+ *           (creating fibril without starting is fine)
+ *
+ * Additionally, locking with a timeout is not possible on this mutex,
+ * and there is no associated condition variable type.
+ * This is a design constraint, not a lack of implementation effort.
+ */
+typedef struct {
+        // TODO: At this point, this is just silly handwaving to hide current
+        //       futex use behind a fibril based abstraction. Later, the imple-
+        //       mentation will change, but the restrictions placed on this type
+        //       will allow it to be simpler and faster than a regular mutex.
+        //       There might also be optional debug checking of the assumptions.
+        //
+        //       Note that a consequence of the restrictions is that if we are
+        //       running on a single thread, no other fibril can ever get to run
+        //       while a fibril has a rmutex locked. That means that for
+        //       single-threaded programs, we can reduce all rmutex locks and
+        //       unlocks to simple branches on a global bool variable.
+
+        futex_t futex;
+} fibril_rmutex_t;
+
+#define FIBRIL_RMUTEX_INITIALIZER(name) \
+        { .futex = FUTEX_INITIALIZE(1) }
+
+#define FIBRIL_RMUTEX_INITIALIZE(name) \
+        fibril_rmutex_t name = FIBRIL_RMUTEX_INITIALIZER(name)
+
+static inline void fibril_rmutex_initialize(fibril_rmutex_t *m)
+{
+        futex_initialize(&m->futex, 1);
+}
+
+static inline void fibril_rmutex_lock(fibril_rmutex_t *m)
+{
+        futex_lock(&m->futex);
+}
+
+static inline bool fibril_rmutex_trylock(fibril_rmutex_t *m)
+{
+        return futex_trylock(&m->futex);
+}
+
+static inline void fibril_rmutex_unlock(fibril_rmutex_t *m)
+{
+        futex_unlock(&m->futex);
+}
 
 typedef struct {