From 052a3c80512fd8c99163f921d53b51800c402ff6 Mon Sep 17 00:00:00 2001
From: Adam Chlipala <adam@chlipala.net>
Date: Thu, 17 Apr 2014 17:41:24 -0400
Subject: uw_register_transactional() can return error codes

---
 doc/manual.tex | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

(limited to 'doc/manual.tex')

diff --git a/doc/manual.tex b/doc/manual.tex
index 98ebaac5..ea866309 100644
--- a/doc/manual.tex
+++ b/doc/manual.tex
@@ -2459,10 +2459,10 @@ void *uw_malloc(uw_context, size_t);
   \item \begin{verbatim}
 typedef void (*uw_callback)(void *);
 typedef void (*uw_callback_with_retry)(void *, int will_retry);
-void uw_register_transactional(uw_context, void *data, uw_callback commit,
-                               uw_callback rollback, uw_callback_with_retry free);
+int uw_register_transactional(uw_context, void *data, uw_callback commit,
+                              uw_callback rollback, uw_callback_with_retry free);
   \end{verbatim}
-  All side effects in Ur/Web programs need to be compatible with transactions, such that any set of actions can be undone at any time.  Thus, you should not perform actions with non-local side effects directly; instead, register handlers to be called when the current transaction is committed or rolled back.  The arguments here give an arbitary piece of data to be passed to callbacks, a function to call on commit, a function to call on rollback, and a function to call afterward in either case to clean up any allocated resources.  A rollback handler may be called after the associated commit handler has already been called, if some later part of the commit process fails.  A free handler is told whether the runtime system expects to retry the current page request after rollback finishes.
+  All side effects in Ur/Web programs need to be compatible with transactions, such that any set of actions can be undone at any time.  Thus, you should not perform actions with non-local side effects directly; instead, register handlers to be called when the current transaction is committed or rolled back.  The arguments here give an arbitary piece of data to be passed to callbacks, a function to call on commit, a function to call on rollback, and a function to call afterward in either case to clean up any allocated resources.  A rollback handler may be called after the associated commit handler has already been called, if some later part of the commit process fails.  A free handler is told whether the runtime system expects to retry the current page request after rollback finishes.  The return value of \texttt{uw\_register\_transactional()} is 0 on success and nonzero on failure (where failure currently only happens when exceeding configured limits on number of transactionals).
 
   Any of the callbacks may be \texttt{NULL}.  To accommodate some stubbornly non-transactional real-world actions like sending an e-mail message, Ur/Web treats \texttt{NULL} \texttt{rollback} callbacks specially.  When a transaction commits, all \texttt{commit} actions that have non-\texttt{NULL} rollback actions are tried before any \texttt{commit} actions that have \texttt{NULL} rollback actions.  Furthermore, an SQL \texttt{COMMIT} is also attempted in between the two phases, so the nicely transactional actions have a chance to influence whether data are committed to the database, while \texttt{NULL}-rollback actions only get run in the first place after committing data.  The reason for all this is that it is \emph{expected} that concurrency interactions will cause database commits to fail in benign ways that call for transaction restart.  A truly non-undoable action should only be run after we are sure the database transaction will commit.
 
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cgit v1.2.3

