PG_FINALLY

This gives an alternative way of catching exceptions, for the common
case where the cleanup code is the same in the error and non-error
cases.  So instead of

    PG_TRY();
    {
        ... code that might throw ereport(ERROR) ...
    }
    PG_CATCH();
    {
        cleanup();
	PG_RE_THROW();
    }
    PG_END_TRY();
    cleanup();

one can write

    PG_TRY();
    {
        ... code that might throw ereport(ERROR) ...
    }
    PG_FINALLY();
    {
        cleanup();
    }
    PG_END_TRY();

Discussion: https://www.postgresql.org/message-id/flat/95a822c3-728b-af0e-d7e5-71890507ae0c%402ndquadrant.com

1 files changed, 37 insertions, 9 deletions

diff --git a/src/include/utils/elog.h b/src/include/utils/elog.h
index ba0b7f6f79c..853c2e0709e 100644
--- a/src/include/utils/elog.h
+++ b/src/include/utils/elog.h
@@ -277,6 +277,25 @@ extern PGDLLIMPORT ErrorContextCallback *error_context_stack;
  * (sub)transaction abort. Failure to do so may leave the system in an
  * inconsistent state for further processing.
  *
+ * For the common case that the error recovery code and the cleanup in the
+ * normal code path are identical, the following can be used instead:
+ *
+ *		PG_TRY();
+ *		{
+ *			... code that might throw ereport(ERROR) ...
+ *		}
+ *		PG_FINALLY();
+ *		{
+ *			... cleanup code ...
+ *		}
+ *      PG_END_TRY();
+ *
+ * The cleanup code will be run in either case, and any error will be rethrown
+ * afterwards.
+ *
+ * You cannot use both PG_CATCH() and PG_FINALLY() in the same
+ * PG_TRY()/PG_END_TRY() block.
+ *
  * Note: while the system will correctly propagate any new ereport(ERROR)
  * occurring in the recovery section, there is a small limit on the number
  * of levels this will work for.  It's best to keep the error recovery
@@ -300,24 +319,33 @@ extern PGDLLIMPORT ErrorContextCallback *error_context_stack;
  */
 #define PG_TRY()  \
 	do { \
-		sigjmp_buf *save_exception_stack = PG_exception_stack; \
-		ErrorContextCallback *save_context_stack = error_context_stack; \
-		sigjmp_buf local_sigjmp_buf; \
-		if (sigsetjmp(local_sigjmp_buf, 0) == 0) \
+		sigjmp_buf *_save_exception_stack = PG_exception_stack; \
+		ErrorContextCallback *_save_context_stack = error_context_stack; \
+		sigjmp_buf _local_sigjmp_buf; \
+		bool _do_rethrow = false; \
+		if (sigsetjmp(_local_sigjmp_buf, 0) == 0) \
 		{ \
-			PG_exception_stack = &local_sigjmp_buf
+			PG_exception_stack = &_local_sigjmp_buf
 
 #define PG_CATCH()	\
 		} \
 		else \
 		{ \
-			PG_exception_stack = save_exception_stack; \
-			error_context_stack = save_context_stack
+			PG_exception_stack = _save_exception_stack; \
+			error_context_stack = _save_context_stack
+
+#define PG_FINALLY() \
+		} \
+		else \
+			_do_rethrow = true; \
+		{
 
 #define PG_END_TRY()  \
 		} \
-		PG_exception_stack = save_exception_stack; \
-		error_context_stack = save_context_stack; \
+		PG_exception_stack = _save_exception_stack; \
+		error_context_stack = _save_context_stack; \
+		if (_do_rethrow) \
+				PG_RE_THROW(); \
 	} while (0)
 
 /*