[patch][commit] Single Mutex for sidutil::blocking_component

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[patch][commit] Single Mutex for sidutil::blocking_component

Dave Brolley-2
Hi,

I've committed the attached patch which simplifies the implementation of
sidutil::blocking_component. The use of two mutex/condition variable
pairs for synchronizing the parent and child threads was unnecessary
and, if you look at the existing code, you will see that they were
always locked/unlocked/blocked in unison. The implementation now uses a
single mutex/condition variable pair.

The patch also adds checking that a return from pthread_cond_wait was
not spontaneous and makes the control_status member volatile for this
purpose.

Tested extensively using the MeP port which is the only committed port
using this class.

Dave

2007-02-19  Dave Brolley  <[hidden email]>

        * sidblockingutil.h (sidutil::blocking_component): Remove
        child_resume_mutex, child_stopped_mutex, chiuld_resume_condition and
        child_stopped_condition. Use a single mutex/condition pair:
        child_sync_mutex and child_sync_condition. Handle spontaneous returns
        from pthread_cond_wait.
        (control_status): Now volatile.


Index: sid/include/sidblockingutil.h
===================================================================
RCS file: /cvs/src/src/sid/include/sidblockingutil.h,v
retrieving revision 1.3
diff -c -p -r1.3 sidblockingutil.h
*** sid/include/sidblockingutil.h 5 Feb 2007 20:28:42 -0000 1.3
--- sid/include/sidblockingutil.h 19 Feb 2007 16:26:33 -0000
*************** namespace sidutil
*** 49,57 ****
        {
  log (10, "%s: child_init\n", name.c_str ());
  assert (child_created);
! // Lock both mutexes
! pthread_mutex_lock (& child_resume_mutex);
! pthread_mutex_lock (& child_stopped_mutex);
        }
 
    protected:
--- 49,56 ----
        {
  log (10, "%s: child_init\n", name.c_str ());
  assert (child_created);
! // Lock the syncronization mutex
! pthread_mutex_lock (& child_sync_mutex);
        }
 
    protected:
*************** namespace sidutil
*** 59,73 ****
        {
  log (10, "%s: parent_init\n", name.c_str ());
 
! // Create mutexes for synchronizing the parent and child threads
! pthread_mutex_init (& child_resume_mutex, NULL);
! pthread_cond_init (& child_resume_condition, NULL);
! pthread_mutex_init (& child_stopped_mutex, NULL);
! pthread_cond_init (& child_stopped_condition, NULL);
!
! // Lock both mutexes
! pthread_mutex_lock (& child_resume_mutex);
! pthread_mutex_lock (& child_stopped_mutex);
  control_status = ctl_parent;
        }
 
--- 58,69 ----
        {
  log (10, "%s: parent_init\n", name.c_str ());
 
! // Create a mutex for synchronizing the parent and child threads
! pthread_mutex_init (& child_sync_mutex, NULL);
! pthread_cond_init (& child_sync_condition, NULL);
!
! // Lock the mutex
! pthread_mutex_lock (& child_sync_mutex);
  control_status = ctl_parent;
        }
 
*************** namespace sidutil
*** 121,139 ****
  // Signal the child to resume
  assert (control_status != ctl_child_start);
  control_status = ctl_child_start;
! pthread_cond_signal (& child_resume_condition);
!
! // Unlock the mutex so that the child can gain control
! pthread_mutex_unlock (& child_resume_mutex);
 
  // Wait for the return signal from the child
! pthread_cond_wait (& child_stopped_condition, & child_stopped_mutex);
!
! // Reacquire the mutex so that the child can gain control
! pthread_mutex_lock (& child_resume_mutex);
 
- // Check the value of control_status
- assert (control_status != ctl_child_start);
  return control_status;
        }
 
--- 117,132 ----
  // Signal the child to resume
  assert (control_status != ctl_child_start);
  control_status = ctl_child_start;
! log (11, "%s: parent signalling the child thread\n", name.c_str ());
! pthread_cond_signal (& child_sync_condition);
 
  // Wait for the return signal from the child
! do {
!  log (11, "%s: parent waiting for child thread\n", name.c_str ());
!  pthread_cond_wait (& child_sync_condition, & child_sync_mutex);
! } while (control_status == ctl_child_start);
! log (11, "%s: parent regains control\n", name.c_str ());
 
  return control_status;
        }
 
*************** namespace sidutil
*** 168,185 ****
 
  // Signal the parent that we're stopped
  log (11, "%s: child signalling the parent thread\n", name.c_str ());
! pthread_cond_signal (& child_stopped_condition);
!
! // Unlock the mutex so that the parent can gain control
! pthread_mutex_unlock (& child_stopped_mutex);
 
  // Wait for a signal to resume
! log (11, "%s: child waiting for parent thread\n", name.c_str ());
! pthread_cond_wait (& child_resume_condition, & child_resume_mutex);
!
! // Reacquire the stopped mutex
! pthread_mutex_lock (& child_stopped_mutex);
! assert (control_status == ctl_child_start);
        }
 
      void set_blockable ()
--- 161,174 ----
 
  // Signal the parent that we're stopped
  log (11, "%s: child signalling the parent thread\n", name.c_str ());
! pthread_cond_signal (& child_sync_condition);
 
  // Wait for a signal to resume
! do {
!  log (11, "%s: child waiting for parent thread\n", name.c_str ());
!  pthread_cond_wait (& child_sync_condition, & child_sync_mutex);
! } while (control_status != ctl_child_start);
! log (11, "%s: child regains control\n", name.c_str ());
        }
 
      void set_blockable ()
*************** namespace sidutil
*** 198,208 ****
      bool child_created;
      pthread_t child_thread;
      void *(*child_thread_function)(void *);
!     pthread_mutex_t child_resume_mutex;
!     pthread_cond_t child_resume_condition;
!     pthread_mutex_t child_stopped_mutex;
!     pthread_cond_t child_stopped_condition;
!     enum
        {
  ctl_parent, ctl_child_start, ctl_child_blocked, ctl_child_complete
        } control_status;
--- 187,195 ----
      bool child_created;
      pthread_t child_thread;
      void *(*child_thread_function)(void *);
!     pthread_mutex_t child_sync_mutex;
!     pthread_cond_t child_sync_condition;
!     volatile enum
        {
  ctl_parent, ctl_child_start, ctl_child_blocked, ctl_child_complete
        } control_status;