fixed unit test bug; logWriters may now return NULL when readers attempt to read before the beginning of the log

src/stasis/logger/inMemoryLog.c

@@ -145,9 +145,15 @@ static const LogEntry * stasis_log_impl_in_memory_read_entry(stasis_log_t* log,
                                                  lsn_t lsn) {
   stasis_log_impl_in_memory * impl = log->impl;
   DEBUG("lsn: %ld\n", lsn);
-  if(lsn >= impl->nextAvailableLSN) { return 0; }
-  assert(lsn-impl->globalOffset >= 0 && lsn-impl->globalOffset< impl->bufferLen);
   readlock(impl->globalOffset_lock, 0);
+  if(lsn >= impl->nextAvailableLSN) {
+    unlock(impl->globalOffset_lock);
+    return NULL;
+  }
+  if(!(lsn-impl->globalOffset >= 0 && lsn-impl->globalOffset< impl->bufferLen)) {
+    unlock(impl->globalOffset_lock);
+    return NULL;
+  }
   LogEntry * ptr = impl->buffer[lsn - impl->globalOffset];
   unlock(impl->globalOffset_lock);
   assert(ptr);

src/stasis/logger/safeWrites.c

@@ -501,7 +501,7 @@ static const LogEntry * readLSNEntry_LogWriter(stasis_log_t * log, const lsn_t L
 
   if(LSN >= sw->nextAvailableLSN) {
     pthread_mutex_unlock(&sw->nextAvailableLSN_mutex);
-    return 0;
+    return NULL;
   }
   pthread_mutex_unlock(&sw->nextAvailableLSN_mutex);
 
@@ -514,7 +514,11 @@ static const LogEntry * readLSNEntry_LogWriter(stasis_log_t * log, const lsn_t L
     assert(flushedLSNInternal(sw) > LSN);
   }
 
-  assert(sw->global_offset <= LSN);
+  if(sw->global_offset > LSN) {
+    // Return NULL; the caller read before the beginning of the log.
+    pthread_mutex_unlock(&sw->read_mutex);
+    return NULL;
+  }
 
   off_t newPosition = LSN - sw->global_offset;
   newPosition = lseek(sw->ro_fd, newPosition, SEEK_SET);

test/stasis/check_logWriter.c

@@ -312,11 +312,11 @@ static void* worker_thread(void * arg) {
 
     if(threshold < 3) {
       if(i > 10) {
-	needToTruncate = 1;
+        needToTruncate = 1;
-	if(lsns[i - 10] > truncated_to) {
+        if(lsns[i - 10] > truncated_to) {
-	  truncated_to = lsns[i - 10];
+          truncated_to = lsns[i - 10];
-	  myTruncVal = truncated_to;
+          myTruncVal = truncated_to;
-	}
+        }
       }
     }
 
@@ -355,9 +355,14 @@ static void* worker_thread(void * arg) {
       pthread_mutex_unlock(&random_mutex);
 
       const LogEntry * e = stasis_log_file->read_entry(stasis_log_file, lsn);
-
+      if(e == NULL) {
-      assert(e->xid == entry+key);
+        pthread_mutex_lock(&random_mutex);
-      freeLogEntry(e);
+        assert(lsn < truncated_to);
+        pthread_mutex_unlock(&random_mutex);
+      } else {
+        assert(e->xid == entry+key);
+        freeLogEntry(e);
+      }
     } else {
       pthread_mutex_unlock(&random_mutex);
     }