score: Add self-contained futex implementation

1 files changed, 199 insertions, 0 deletions

diff --git a/cpukit/score/src/futex.c b/cpukit/score/src/futex.c
new file mode 100644
index 0000000000..2ec38a3747
--- /dev/null
+++ b/cpukit/score/src/futex.c
@@ -0,0 +1,199 @@
+/*
+ * Copyright (c) 2015 embedded brains GmbH.  All rights reserved.
+ *
+ *  embedded brains GmbH
+ *  Dornierstr. 4
+ *  82178 Puchheim
+ *  Germany
+ *  <rtems@embedded-brains.de>
+ *
+ * The license and distribution terms for this file may be
+ * found in the file LICENSE in this distribution or at
+ * http://www.rtems.org/license/LICENSE.
+ */
+
+#if HAVE_CONFIG_H
+  #include "config.h"
+#endif
+
+#if HAVE_STRUCT__THREAD_QUEUE_QUEUE
+
+#include <sys/lock.h>
+#include <errno.h>
+
+#include <rtems/score/atomic.h>
+#include <rtems/score/chainimpl.h>
+#include <rtems/score/threadimpl.h>
+#include <rtems/score/threadqimpl.h>
+
+#define FUTEX_TQ_OPERATIONS &_Thread_queue_Operations_FIFO
+
+typedef struct {
+  Thread_queue_Syslock_queue Queue;
+} Futex_Control;
+
+RTEMS_STATIC_ASSERT(
+  offsetof( Futex_Control, Queue )
+    == offsetof( struct _Futex_Control, _Queue ),
+  FUTEX_CONTROL_QUEUE
+);
+
+RTEMS_STATIC_ASSERT(
+  sizeof( Futex_Control ) == sizeof( struct _Futex_Control ),
+  FUTEX_CONTROL_SIZE
+);
+
+static Futex_Control *_Futex_Get( struct _Futex_Control *_futex )
+{
+  return (Futex_Control *) _futex;
+}
+
+static Thread_Control *_Futex_Queue_acquire(
+  Futex_Control    *futex,
+  ISR_lock_Context *lock_context
+)
+{
+  Thread_Control *executing;
+
+  _ISR_lock_ISR_disable( lock_context );
+  executing = _Thread_Executing;
+  _Thread_queue_Queue_acquire_critical(
+    &futex->Queue.Queue,
+    &executing->Potpourri_stats,
+    lock_context
+  );
+
+  return executing;
+}
+
+static void _Futex_Queue_release(
+  Futex_Control    *futex,
+  ISR_lock_Context *lock_context
+)
+{
+  _Thread_queue_Queue_release( &futex->Queue.Queue, lock_context );
+}
+
+int _Futex_Wait( struct _Futex_Control *_futex, int *uaddr, int val )
+{
+  Futex_Control    *futex;
+  ISR_lock_Context  lock_context;
+  Thread_Control   *executing;
+  int               eno;
+
+  futex = _Futex_Get( _futex );
+  executing = _Futex_Queue_acquire( futex, &lock_context );
+
+  if ( *uaddr == val ) {
+    _Thread_queue_Enqueue_critical(
+      &futex->Queue.Queue,
+      FUTEX_TQ_OPERATIONS,
+      executing,
+      STATES_WAITING_FOR_SYS_LOCK_FUTEX,
+      0,
+      0,
+      &lock_context
+    );
+    eno = 0;
+  } else {
+    _Futex_Queue_release( futex, &lock_context );
+    eno = EWOULDBLOCK;
+  }
+
+  return eno;
+}
+
+/*
+ * Use a noinline function to force the compiler to set up and tear down the
+ * large stack frame only in the slow case.
+ */
+static __attribute__((noinline)) int _Futex_Wake_slow(
+  Futex_Control      *futex,
+  int                 count,
+  Thread_queue_Heads *heads,
+  ISR_lock_Context   *lock_context
+)
+{
+  Chain_Control  unblock;
+  Chain_Node    *node;
+  Chain_Node    *tail;
+  int            woken;
+
+  woken = 0;
+  _Chain_Initialize_empty( &unblock );
+
+  while ( count > 0 && heads != NULL ) {
+    const Thread_queue_Operations *operations;
+    Thread_Control                *first;
+    bool                           do_unblock;
+
+    operations = FUTEX_TQ_OPERATIONS;
+    first = ( *operations->first )( heads );
+
+    do_unblock = _Thread_queue_Extract_locked(
+      &futex->Queue.Queue,
+      operations,
+      first
+    );
+    if (do_unblock) {
+      _Chain_Append_unprotected( &unblock, &first->Wait.Node.Chain );
+    }
+
+    ++woken;
+    --count;
+    heads = futex->Queue.Queue.heads;
+  }
+
+  node = _Chain_First( &unblock );
+  tail = _Chain_Tail( &unblock );
+
+  if ( node != tail ) {
+    Per_CPU_Control *cpu_self;
+
+    cpu_self = _Thread_Dispatch_disable_critical( lock_context );
+    _Futex_Queue_release( futex, lock_context );
+
+    do {
+      Thread_Control *thread;
+      Chain_Node     *next;
+
+      next = _Chain_Next( node );
+      thread = THREAD_CHAIN_NODE_TO_THREAD( node );
+      _Thread_Unblock( thread );
+
+      node = next;
+    } while ( node != tail );
+
+    _Thread_Dispatch_enable( cpu_self );
+  } else {
+    _Futex_Queue_release( futex, lock_context );
+  }
+
+  return woken;
+}
+
+int _Futex_Wake( struct _Futex_Control *_futex, int count )
+{
+  Futex_Control      *futex;
+  ISR_lock_Context    lock_context;
+  Thread_queue_Heads *heads;
+
+  futex = _Futex_Get( _futex );
+  _Futex_Queue_acquire( futex, &lock_context );
+
+  /*
+   * For some synchronization objects like barriers the _Futex_Wake() must be
+   * called in the fast path.  Normally there are no threads on the queue, so
+   * check this condition early.
+   */
+  heads = futex->Queue.Queue.heads;
+  if ( __predict_true( heads == NULL ) ) {
+    _Futex_Queue_release( futex, &lock_context );
+
+    return 0;
+  }
+
+  return _Futex_Wake_slow( futex, count, heads, &lock_context );
+}
+
+#endif /* HAVE_STRUCT__THREAD_QUEUE_QUEUE */