fixed mantis 192 - Concurrency bug in channel access to local DB

src/db/dbContextReadNotifyCache.cpp

@@ -14,7 +14,6 @@
  */
 
 #include "epicsMutex.h"
-#include "tsFreeList.h"
 
 #include "cadef.h" // this can be eliminated when the callbacks use the new interface
 #include "db_access.h" // should be eliminated here in the future
@@ -25,35 +24,30 @@
 #include "dbCAC.h"
 
 dbContextReadNotifyCache::dbContextReadNotifyCache ( epicsMutex & mutexIn ) :
-    readNotifyCacheSize ( 0 ), mutex ( mutexIn ), pReadNotifyCache ( 0 )
+    _mutex ( mutexIn )
 {
 }
 
-dbContextReadNotifyCache::~dbContextReadNotifyCache ()
-{
-	delete this->pReadNotifyCache;
-}
+class privateAutoDestroyPtr {
+public:
+    privateAutoDestroyPtr ( 
+        dbContextReadNotifyCacheAllocator & allocator, unsigned long size ) :
+        _allocator ( allocator ), _p ( allocator.alloc ( size ) ) {}
+    ~privateAutoDestroyPtr () { _allocator.free ( _p ); }
+	char * get () const { return _p; }              
+private:
+    dbContextReadNotifyCacheAllocator & _allocator;
+    char * _p;
+	privateAutoDestroyPtr ( const privateAutoDestroyPtr & );
+	privateAutoDestroyPtr & operator = ( const privateAutoDestroyPtr & );
+};
 
-void dbContextReadNotifyCache::show ( 
-    epicsGuard < epicsMutex > & guard, unsigned level ) const
-{
-    guard.assertIdenticalMutex ( this->mutex );
-
-    if ( level > 0 ) {
-        printf ( "\tget call back cache location %p, and its size %lu\n", 
-            static_cast <void *> ( this->pReadNotifyCache ), 
-            this->readNotifyCacheSize );
-    }
-}
-
-// extra effort taken here to not hold the lock when caslling the callback
+// extra effort taken here to not hold the lock when calling the callback
 void dbContextReadNotifyCache::callReadNotify ( 
     epicsGuard < epicsMutex > & guard, struct dbAddr & addr, 
 	unsigned type, unsigned long count, cacReadNotify & notify )
 {
-    guard.assertIdenticalMutex ( this->mutex );
-
-    unsigned long size = dbr_size_n ( type, count );
+    guard.assertIdenticalMutex ( _mutex );
 
     if ( type > INT_MAX ) {
         notify.exception ( guard, ECA_BADTYPE, 
@@ -62,38 +56,108 @@ void dbContextReadNotifyCache::callReadNotify (
         return;
     }
 
-    if ( count > static_cast < unsigned > ( INT_MAX ) || 
-		count > static_cast < unsigned > ( addr.no_elements ) ) {
+    if ( addr.no_elements < 0 ) {
+        notify.exception ( guard, ECA_BADCOUNT, 
+            "database has negetive element count",
+            type, count);
+        return;
+    }
+
+    if ( count > static_cast < unsigned > ( addr.no_elements ) ) {
         notify.exception ( guard, ECA_BADCOUNT, 
             "element count out of range (high side)",
             type, count);
         return;
     }
 
-    if ( this->readNotifyCacheSize < size) {
-        char * pTmp = new char [size];
-        if ( ! pTmp ) {
-            notify.exception ( guard, ECA_ALLOCMEM, 
-                "unable to allocate callback cache",
-                type, count );
-            return;
-        }
-        delete [] this->pReadNotifyCache;
-        this->pReadNotifyCache = pTmp;
-        this->readNotifyCacheSize = size;
-    }
+    unsigned long size = dbr_size_n ( type, count );
+    privateAutoDestroyPtr ptr ( _allocator, size );
     int status;
     {
         epicsGuardRelease < epicsMutex > unguard ( guard );
         status = db_get_field ( &addr, static_cast <int> ( type ), 
-                    this->pReadNotifyCache, static_cast <int> ( count ), 0 );
+                    ptr.get (), static_cast <int> ( count ), 0 );
     }
     if ( status ) {
         notify.exception ( guard, ECA_GETFAIL, 
             "db_get_field() completed unsuccessfuly",
-            type, count);
+            type, count );
     }
     else { 
-        notify.completion ( guard, type, count, this->pReadNotifyCache );
+        notify.completion ( 
+            guard, type, count, ptr.get () );
     }
 }
+
+void dbContextReadNotifyCache::show ( 
+    epicsGuard < epicsMutex > & guard, unsigned level ) const
+{
+    guard.assertIdenticalMutex ( _mutex );
+
+    printf ( "dbContextReadNotifyCache\n" );
+    if ( level > 0 ) {
+        this->_allocator.show ( level - 1 );
+    }
+}
+
+dbContextReadNotifyCacheAllocator::dbContextReadNotifyCacheAllocator () :
+    _readNotifyCacheSize ( 0 ), _pReadNotifyCache ( 0 )
+{
+}
+
+dbContextReadNotifyCacheAllocator::~dbContextReadNotifyCacheAllocator ()
+{
+    this->reclaimAllCacheEntries ();
+}
+
+void dbContextReadNotifyCacheAllocator::reclaimAllCacheEntries ()
+{
+
+    while ( _pReadNotifyCache ) {
+        cacheElem_t * pNext = _pReadNotifyCache->pNext;
+        delete [] _pReadNotifyCache;
+        _pReadNotifyCache = pNext;
+    }
+}
+
+char * dbContextReadNotifyCacheAllocator::alloc ( unsigned long size )
+{
+    if ( size > _readNotifyCacheSize ) {
+        this->reclaimAllCacheEntries ();
+        _readNotifyCacheSize = size;
+    }
+
+    cacheElem_t * pAlloc = _pReadNotifyCache;
+    if ( pAlloc ) {
+        _pReadNotifyCache = pAlloc->pNext;
+    }
+    else {
+        size_t nElem = _readNotifyCacheSize / sizeof ( cacheElem_t );
+        pAlloc = new cacheElem_t [ nElem + 1 ];
+    }
+    return reinterpret_cast < char * > ( pAlloc );
+}
+
+void dbContextReadNotifyCacheAllocator::free ( char * pFree )
+{
+    cacheElem_t * pAlloc = reinterpret_cast < cacheElem_t * > ( pFree );
+    pAlloc->pNext = _pReadNotifyCache;
+    _pReadNotifyCache = pAlloc;
+}
+
+void dbContextReadNotifyCacheAllocator::show ( unsigned level ) const
+{
+    printf ( "dbContextReadNotifyCacheAlocator\n" );
+    if ( level > 0 ) {
+        size_t count =0;
+        cacheElem_t * pNext = _pReadNotifyCache;
+        while ( pNext ) {
+            pNext = _pReadNotifyCache->pNext;
+            count++;
+        }
+        printf ( "\tcount %u and size %lu\n", 
+            count, _readNotifyCacheSize );
+    }
+}
+
+