From dd3baf0ce4634685b6af90581a4afeb742dc67ff Mon Sep 17 00:00:00 2001
From: Jeff Hill <johill@lanl.gov>
Date: Fri, 13 Jul 2001 23:12:41 +0000
Subject: [PATCH] fixed and also simplified locking logic

---
 src/ca/cac.cpp | 132 ++++++++++++++++++++++---------------------------
 src/ca/cac.h   |   3 --
 2 files changed, 58 insertions(+), 77 deletions(-)

diff --git a/src/ca/cac.cpp b/src/ca/cac.cpp
index 1f0b3f61e..395f02963 100644
--- a/src/ca/cac.cpp
+++ b/src/ca/cac.cpp
@@ -119,11 +119,9 @@ cac::cac ( cacNotify &notifyIn, bool enablePreemptiveCallbackIn ) :
     recvProcessEnableRefCount ( 0u ),
     pndRecvCnt ( 0u ), 
     readSeq ( 0u ),
-    recvProcessCompletionSignalRequestCount ( 0u ),
     enablePreemptiveCallback ( enablePreemptiveCallbackIn ),
     ioInProgress ( false ),
-    recvProcessThreadExitRequest ( false ),
-    recvProcessPending ( false )
+    recvProcessThreadExitRequest ( false )
 {
 	long status;
     unsigned abovePriority;
@@ -223,7 +221,10 @@ cac::~cac ()
     if ( this->pRecvProcessThread ) {
         this->recvProcessThreadExitRequest = true;
         this->recvProcessActivityEvent.signal ();
-        this->enableCallbackPreemption ();
+        {
+            epicsAutoMutex autoMutex ( this->mutex );
+            this->enableCallbackPreemption ();
+        }
         this->recvProcessThreadExit.wait ();
         delete this->pRecvProcessThread;
     }
@@ -577,8 +578,10 @@ void cac::blockForEventAndEnableCallbacks ( epicsEvent &event, double timeout )
     this->disableCallbackPreemption ();
 }
 
-int cac::pendEvent ( const double &timeout )
+int cac::pendEvent ( const double & timeout )
 {
+    epicsTime current = epicsTime::getCurrent ();
+
     // prevent recursion nightmares by disabling calls to 
     // pendIO () from within a CA callback
     if ( this->recvProcessThreadIsCurrentThread () ) {
@@ -590,39 +593,31 @@ int cac::pendEvent ( const double &timeout )
 
         this->flushRequestPrivate ();
 
-        bool waitForSignal;
-        if ( this->recvProcessPending ) {
-            this->recvProcessCompletionSignalRequestCount++;
-            waitForSignal = true;
+        // process at least once if preemptive callback
+        // isnt enabled (this avoids complications associated
+        // with forcing the recv processing thread to run.
+        if ( ! this->enablePreemptiveCallback && 
+                this->recvProcessEnableRefCount == 0 ) {
+            this->processRecvBacklog ();
+        }
+
+        double elapsed = epicsTime::getCurrent() - current;
+        double delay;
+
+        if ( timeout > elapsed ) {
+            delay = timeout - elapsed;
         }
         else {
-            waitForSignal = false;
+            delay = 0.0;
         }
 
-        this->enableCallbackPreemption ();
-
-        {
-            epicsAutoMutexRelease autoMutexRelease ( this->mutex );
-            if ( timeout == 0.0 ) {
-                while ( true ) {
-                    epicsThreadSleep ( 60.0 );
-                }
-            }
-            else if ( timeout >= CAC_SIGNIFICANT_DELAY ) {
-                epicsThreadSleep ( timeout );
-            }
-            if ( waitForSignal ) {
-                this->recvProcessCompleted.wait ();
-            }
-        }
-
-        this->disableCallbackPreemption ();
-
-        if ( waitForSignal ) {
-            this->recvProcessCompletionSignalRequestCount--;
-            if ( this->recvProcessCompletionSignalRequestCount ) {
-                this->recvProcessCompleted.signal ();
+        if ( delay >= CAC_SIGNIFICANT_DELAY ) {
+            this->enableCallbackPreemption ();
+            {
+                epicsAutoMutexRelease autoMutexRelease ( this->mutex );
+                epicsThreadSleep ( delay );
             }
+            this->disableCallbackPreemption ();
         }
     }
 
@@ -674,28 +669,24 @@ void cac::registerService ( cacService &service )
 
 void cac::startRecvProcessThread ()
 {
-    bool newThread = false;
-    {
-        epicsAutoMutex epicsMutex ( this->mutex );
-        if ( ! this->pRecvProcessThread ) {
-            unsigned priorityOfProcess;
-            epicsThreadBooleanStatus tbs  = epicsThreadLowestPriorityLevelAbove ( 
-                this->getInitializingThreadsPriority (), &priorityOfProcess );
-            if ( tbs != epicsThreadBooleanStatusSuccess ) {
-                priorityOfProcess = this->getInitializingThreadsPriority ();
-            }
-
-            this->pRecvProcessThread = new epicsThread ( *this, "CAC-recv-process",
-                epicsThreadGetStackSize ( epicsThreadStackSmall ), priorityOfProcess );
-            if ( ! this->pRecvProcessThread ) {
-                throw std::bad_alloc ();
-            }
-            this->pRecvProcessThread->start ();
-            newThread = true;
+    epicsAutoMutex epicsMutex ( this->mutex );
+    if ( ! this->pRecvProcessThread ) {
+        unsigned priorityOfProcess;
+        epicsThreadBooleanStatus tbs  = epicsThreadLowestPriorityLevelAbove ( 
+            this->getInitializingThreadsPriority (), &priorityOfProcess );
+        if ( tbs != epicsThreadBooleanStatusSuccess ) {
+            priorityOfProcess = this->getInitializingThreadsPriority ();
+        }
+
+        this->pRecvProcessThread = new epicsThread ( *this, "CAC-recv-process",
+            epicsThreadGetStackSize ( epicsThreadStackSmall ), priorityOfProcess );
+        if ( ! this->pRecvProcessThread ) {
+            throw std::bad_alloc ();
+        }
+        this->pRecvProcessThread->start ();
+        if ( this->enablePreemptiveCallback ) {
+            this->enableCallbackPreemption ();
         }
-    }
-    if ( this->enablePreemptiveCallback && newThread ) {
-        this->enableCallbackPreemption ();
     }
 }
 
@@ -704,17 +695,10 @@ void cac::run ()
 {
     this->attachToClientCtx ();
     while ( ! this->recvProcessThreadExitRequest ) {
-        bool wakeupNeeded;
         {
-            this->recvProcessPending = true;
             epicsAutoMutex autoMutexPCB ( this->preemptiveCallbackLock );
             epicsAutoMutex autoMutex ( this->mutex );
             this->processRecvBacklog ();
-            this->recvProcessPending = false;
-            wakeupNeeded = this->recvProcessCompletionSignalRequestCount > 0u;
-        }
-        if ( wakeupNeeded ) {
-            this->recvProcessCompleted.signal ();
         }
         this->recvProcessActivityEvent.wait ();
     }
@@ -802,20 +786,14 @@ void cac::enableCallbackPreemption ()
 // lock must already be applied
 void cac::disableCallbackPreemption ()
 {
-    if ( this->recvProcessEnableRefCount == 1u ) {
-        if ( ! this->preemptiveCallbackLock.tryLock () ) {
-            {
-                epicsAutoMutexRelease autoMutexRelease ( this->mutex );
-                this->preemptiveCallbackLock.lock ();
-            }
-            // in case some thread enabled it while this->mutex was unlocked
-            if ( this->recvProcessEnableRefCount > 1u ) {
-                this->preemptiveCallbackLock.unlock ();
-            }
-        }
-    }
     assert ( this->recvProcessEnableRefCount > 0u );
     this->recvProcessEnableRefCount--;
+    if ( this->recvProcessEnableRefCount == 0u ) {
+        if ( ! this->preemptiveCallbackLock.tryLock () ) {
+            epicsAutoMutexRelease autoMutexRelease ( this->mutex );
+            this->preemptiveCallbackLock.lock ();
+        }
+    }
 }
 
 void cac::repeaterSubscribeConfirmNotify ()
@@ -1045,7 +1023,13 @@ void cac::ioCancel ( nciu &chan, const cacChannel::ioid &id )
             if ( pSubscr ) {
                 chan.getPIIU()->subscriptionCancelRequest ( chan, *pSubscr );
             }
-            if ( pRecvProcessThread->isCurrentThread() ) {
+            //
+            // if preemptive callback is not enabled then 
+            // the code will block until the recv process 
+            // thread is idle before returning control back
+            // to the user
+            if ( ! this->enablePreemptiveCallback ||
+                pRecvProcessThread->isCurrentThread() ) {
                 signalNeeded = false;
             }
             else {
diff --git a/src/ca/cac.h b/src/ca/cac.h
index 41e956613..d686fa4c4 100644
--- a/src/ca/cac.h
+++ b/src/ca/cac.h
@@ -163,7 +163,6 @@ private:
     epicsEvent              notifyCompletionEvent;
     epicsEvent              recvProcessActivityEvent;
     epicsEvent              recvProcessThreadExit;
-    epicsEvent              recvProcessCompleted;
     epicsEvent              ioDone;
     epicsTimerQueueActive   *pTimerQueue;
     char                    *pUserName;
@@ -182,11 +181,9 @@ private:
     unsigned                recvProcessEnableRefCount;
     unsigned                pndRecvCnt;
     unsigned                readSeq;
-    unsigned                recvProcessCompletionSignalRequestCount;
     bool                    enablePreemptiveCallback;
     bool                    ioInProgress;
     bool                    recvProcessThreadExitRequest;
-    bool                    recvProcessPending;
 
     void processRecvBacklog ();
     void flushRequestPrivate ();