arangodb/Documentation/locks.diff

diff --git a/arangod/VocBase/compactor.c b/arangod/VocBase/compactor.c
index 2809b17..19a81e0 100644
--- a/arangod/VocBase/compactor.c
+++ b/arangod/VocBase/compactor.c
@@ -404,11 +404,13 @@ static void CompactifySimCollection (TRI_sim_collection_t* sim) {
   size_t n;
   size_t i;
 
+  if (! TRI_TRY_READ_LOCK_DATAFILES_SIM_COLLECTION(sim)) {
+    return;
+  }
+  
   TRI_InitVector(&vector, TRI_UNKNOWN_MEM_ZONE, sizeof(TRI_doc_datafile_info_t));
 
   // copy datafile information
-  TRI_READ_LOCK_DATAFILES_SIM_COLLECTION(sim);
-
   n = sim->base.base._datafiles._length;
 
   for (i = 0;  i < n;  ++i) {
diff --git a/arangod/VocBase/simple-collection.h b/arangod/VocBase/simple-collection.h
index 1a8c2e7..73132b5 100644
--- a/arangod/VocBase/simple-collection.h
+++ b/arangod/VocBase/simple-collection.h
@@ -53,6 +53,13 @@ extern "C" {
 ////////////////////////////////////////////////////////////////////////////////
 
 ////////////////////////////////////////////////////////////////////////////////
+/// @brief tries to read lock the journal files and the parameter file
+////////////////////////////////////////////////////////////////////////////////
+
+#define TRI_TRY_READ_LOCK_DATAFILES_SIM_COLLECTION(a) \
+  TRI_TryReadLockReadWriteLock(&(a)->_lock)
+
+////////////////////////////////////////////////////////////////////////////////
 /// @brief read locks the journal files and the parameter file
 ////////////////////////////////////////////////////////////////////////////////
 
diff --git a/arangod/VocBase/synchroniser.c b/arangod/VocBase/synchroniser.c
index fb0e496..cb5eb91 100644
--- a/arangod/VocBase/synchroniser.c
+++ b/arangod/VocBase/synchroniser.c
@@ -138,7 +138,7 @@ static bool CheckJournalSimCollection (TRI_sim_collection_t* sim) {
   bool worked;
   size_t i;
   size_t n;
-
+      
   worked = false;
   base = &sim->base.base;
 
@@ -205,7 +205,7 @@ static bool CheckSyncCompactorSimCollection (TRI_sim_collection_t* sim) {
   double ti;
   size_t i;
   size_t n;
-
+  
   worked = false;
   base = &sim->base.base;
 
@@ -266,7 +266,7 @@ static bool CheckCompactorSimCollection (TRI_sim_collection_t* sim) {
   bool worked;
   size_t i;
   size_t n;
-
+  
   worked = false;
   base = &sim->base.base;
 
@@ -365,8 +365,10 @@ void TRI_SynchroniserVocBase (void* data) {
       bool result;
 
       collection = collections._buffer[i];
-
-      TRI_READ_LOCK_STATUS_VOCBASE_COL(collection);
+  
+      if (! TRI_TRY_READ_LOCK_DATAFILES_SIM_COLLECTION(collection)) {
+        continue;
+      }
 
       if (collection->_status != TRI_VOC_COL_STATUS_LOADED) {
         TRI_READ_UNLOCK_STATUS_VOCBASE_COL(collection);
diff --git a/lib/BasicsC/locks-posix.c b/lib/BasicsC/locks-posix.c
index 6ea05f9..150d727 100644
--- a/lib/BasicsC/locks-posix.c
+++ b/lib/BasicsC/locks-posix.c
@@ -230,6 +230,18 @@ void TRI_DestroyReadWriteLock (TRI_read_write_lock_t* lock) {
 ////////////////////////////////////////////////////////////////////////////////
 
 ////////////////////////////////////////////////////////////////////////////////
+/// @brief tries to read lock read-write lock
+////////////////////////////////////////////////////////////////////////////////
+
+bool TRI_TryReadLockReadWriteLock (TRI_read_write_lock_t* lock) {
+  int rc;
+
+  rc = pthread_rwlock_tryrdlock(lock);
+
+  return (rc == 0);
+}
+
+////////////////////////////////////////////////////////////////////////////////
 /// @brief read locks read-write lock
 ////////////////////////////////////////////////////////////////////////////////
 
diff --git a/lib/BasicsC/locks-win32.c b/lib/BasicsC/locks-win32.c
index 73b0a4b..72b720b 100644
--- a/lib/BasicsC/locks-win32.c
+++ b/lib/BasicsC/locks-win32.c
@@ -267,6 +267,27 @@ static void DecrementReaders (TRI_read_write_lock_t* lock) {
 ////////////////////////////////////////////////////////////////////////////////
 
 ////////////////////////////////////////////////////////////////////////////////
+/// @brief tries to read lock a read-write lock
+////////////////////////////////////////////////////////////////////////////////
+
+bool TRI_TryReadLockReadWriteLock (TRI_read_write_lock_t* lock) {
+  WaitForSingleObject(lock->_writerEvent, 10); // 10 millis timeout
+
+  EnterCriticalSection(&lock->_lockReaders);
+  IncrementReaders(lock);
+  LeaveCriticalSection(&lock->_lockReaders);
+
+  if (WaitForSingleObject(lock->_writerEvent, 0) != WAIT_OBJECT_0) {
+    EnterCriticalSection(&lock->_lockReaders);
+    DecrementReaders(lock);
+    LeaveCriticalSection(&lock->_lockReaders);
+    return false;
+  }
+
+  return true;
+}
+
+////////////////////////////////////////////////////////////////////////////////
 /// @brief read locks read-write lock
 ////////////////////////////////////////////////////////////////////////////////
 
diff --git a/lib/BasicsC/locks.h b/lib/BasicsC/locks.h
index 5b37860..2146416 100644
--- a/lib/BasicsC/locks.h
+++ b/lib/BasicsC/locks.h
@@ -229,6 +229,12 @@ void TRI_DestroyReadWriteLock (TRI_read_write_lock_t* lock);
 ////////////////////////////////////////////////////////////////////////////////
 
 ////////////////////////////////////////////////////////////////////////////////
+/// @brief tries to read lock read-write lock
+////////////////////////////////////////////////////////////////////////////////
+
+bool TRI_TryReadLockReadWriteLock (TRI_read_write_lock_t* lock);
+
+////////////////////////////////////////////////////////////////////////////////
 /// @brief read locks read-write lock
 ////////////////////////////////////////////////////////////////////////////////