Implement basic sleeping locks for gnumach

* kern/atomic.h: New file.
* kern/kmutex.h: New file.
* kern/kmutex.c: New file.
* Makefrag.am (libkernel_a_SOURCES): Add atomic.h, kmutex.h, kmutex.c.
* kern/sched_prim.h (thread_wakeup_prim): Make it return boolean_t.
* kern/sched_prim.c (thread_wakeup_prim): Return TRUE if we woke a
thread, and FALSE otherwise.

1 files changed, 76 insertions, 0 deletions

diff --git a/kern/kmutex.c b/kern/kmutex.c
new file mode 100644
index 00000000..5926d1d9
--- /dev/null
+++ b/kern/kmutex.c
@@ -0,0 +1,76 @@
+/* Copyright (C) 2017 Free Software Foundation, Inc.
+   Contributed by Agustina Arzille <avarzille@riseup.net>, 2017.
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License
+   as published by the Free Software Foundation; either
+   version 2 of the license, or (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public
+   License along with this program; if not, see
+   <http://www.gnu.org/licenses/>.
+*/
+
+#include <kern/kmutex.h>
+#include <kern/atomic.h>
+#include <kern/sched_prim.h>
+#include <kern/thread.h>
+
+void kmutex_init (struct kmutex *mtxp)
+{
+  mtxp->state = KMUTEX_AVAIL;
+  simple_lock_init (&mtxp->lock);
+}
+
+kern_return_t kmutex_lock (struct kmutex *mtxp, boolean_t interruptible)
+{
+  check_simple_locks ();
+
+  if (atomic_cas_acq (&mtxp->state, KMUTEX_AVAIL, KMUTEX_LOCKED))
+    /* Unowned mutex - We're done. */
+    return (KERN_SUCCESS);
+
+  /* The mutex is locked. We may have to sleep. */
+  simple_lock (&mtxp->lock);
+  if (atomic_swap_acq (&mtxp->state, KMUTEX_CONTENDED) == KMUTEX_AVAIL)
+    {
+      /* The mutex was released in-between. */
+      simple_unlock (&mtxp->lock);
+      return (KERN_SUCCESS);
+    }
+
+  /* Sleep and check the result value of the waiting, in order to
+   * inform our caller if we were interrupted or not. Note that
+   * we don't need to set again the mutex state. The owner will
+   * handle that in every case. */
+  thread_sleep ((event_t)mtxp, (simple_lock_t)&mtxp->lock, interruptible);
+  return (current_thread()->wait_result == THREAD_AWAKENED ?
+    KERN_SUCCESS : KERN_INTERRUPTED);
+}
+
+kern_return_t kmutex_trylock (struct kmutex *mtxp)
+{
+  return (atomic_cas_acq (&mtxp->state, KMUTEX_AVAIL, KMUTEX_LOCKED) ?
+    KERN_SUCCESS : KERN_FAILURE);
+}
+
+void kmutex_unlock (struct kmutex *mtxp)
+{
+  if (atomic_cas_rel (&mtxp->state, KMUTEX_LOCKED, KMUTEX_AVAIL))
+    /* No waiters - We're done. */
+    return;
+
+  simple_lock (&mtxp->lock);
+
+  if (!thread_wakeup_one ((event_t)mtxp))
+    /* Any threads that were waiting on this mutex were
+     * interrupted and left - Reset the mutex state. */
+    mtxp->state = KMUTEX_AVAIL;
+
+  simple_unlock (&mtxp->lock);
+}