task: Add new cancellation point interface, check_cancellation_point().

include/nuttx/cancelpt.h

@@ -2,7 +2,7 @@
  * include/nuttx/cancelpt.h
  * Definitions related to cancellation points
  *
- *   Copyright (C) 2016 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2016-2017 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -144,6 +144,31 @@ void leave_cancellation_point(void);
 #  define leave_cancellation_point()
 #endif
 
+/****************************************************************************
+ * Name: check_cancellation_point
+ *
+ * Description:
+ *   Returns true if:
+ *
+ *   1. Deferred cancellation does applies to this thread,
+ *   2. We are within a cancellation point (i.e., the nesting level in the
+ *      TCB is greater than zero).
+ *
+ * Input Parameters:
+ *   None
+ *
+ * Returned Value
+ *   true is returned if a cancellation is pending but cannot be performed
+ *   now due to the nesting level.
+ *
+ ****************************************************************************/
+
+#ifdef CONFIG_CANCELLATION_POINTS
+bool check_cancellation_point(void);
+#else
+#  define check_cancellation_point() false
+#endif
+
 #undef EXTERN
 #ifdef __cplusplus
 }

sched/task/task_cancelpt.c

@@ -1,7 +1,7 @@
 /****************************************************************************
  * sched/task/task_cancelpt.c
  *
- *   Copyright (C) 2016 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2016-2017 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -260,6 +260,59 @@ void leave_cancellation_point(void)
   sched_unlock();
 }
 
+/****************************************************************************
+ * Name: check_cancellation_point
+ *
+ * Description:
+ *   Returns true if:
+ *
+ *   1. Deferred cancellation does applies to this thread,
+ *   2. We are within a cancellation point (i.e., the nesting level in the
+ *      TCB is greater than zero).
+ *
+ * Input Parameters:
+ *   None
+ *
+ * Returned Value
+ *   true is returned if a cancellation is pending but cannot be performed
+ *   now due to the nesting level.
+ *
+ ****************************************************************************/
+
+bool check_cancellation_point(void)
+{
+  FAR struct tcb_s *tcb = this_task();
+  bool ret = false;
+
+  /* Disabling pre-emption should provide sufficient protection.  We only
+   * need the TCB to be stationary (no interrupt level modification is
+   * anticipated).
+   *
+   * REVISIT: is locking the scheduler sufficent in SMP mode?
+   */
+
+  sched_lock();
+
+  /* If cancellation is disabled on this thread or if this thread is using
+   * asynchronous cancellation, then return false.
+   *
+   * If the cpcount count is greater than zero, then we within a
+   * cancellation and will true if there is a pending cancellation.
+   */
+
+  if (((tcb->flags & TCB_FLAG_NONCANCELABLE) == 0 &&
+       (tcb->flags & TCB_FLAG_CANCEL_DEFERRED) != 0) ||
+      tcb->cpcount > 0)
+    {
+      /* Check if there is a pending cancellation.  If so, return true. */
+
+      ret = ((tcb->flags & TCB_FLAG_CANCEL_PENDING) != 0);
+    }
+
+  sched_unlock();
+  return ret;
+}
+
 /****************************************************************************
  * Name: notify_cancellation
  *