diff options
| -rw-r--r-- | doc/manual.tex | 2 | ||||
| -rw-r--r-- | src/c/urweb.c | 52 |
2 files changed, 40 insertions, 14 deletions
diff --git a/doc/manual.tex b/doc/manual.tex index e46089d0..98ebaac5 100644 --- a/doc/manual.tex +++ b/doc/manual.tex @@ -2464,7 +2464,7 @@ void uw_register_transactional(uw_context, void *data, uw_callback commit, \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. - 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. Thus, if a single execution uses only one non-transactional action, and if that action never fails partway through its execution while still causing an observable side effect, then Ur/Web can maintain the transactional abstraction. + 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. When a request handler ends with multiple pending transactional actions, their handlers are run in a first-in-last-out stack-like order, wherever the order would otherwise be ambiguous. diff --git a/src/c/urweb.c b/src/c/urweb.c index df137e77..7417e4b7 100644 --- a/src/c/urweb.c +++ b/src/c/urweb.c @@ -3304,32 +3304,58 @@ int uw_commit(uw_context ctx) { } } - for (i = ctx->used_transactionals-1; i >= 0; --i) - if (ctx->transactionals[i].rollback == NULL) - if (ctx->transactionals[i].commit) { - ctx->transactionals[i].commit(ctx->transactionals[i].data); - if (uw_has_error(ctx)) { - uw_rollback(ctx, 0); - return 0; - } - } - if (ctx->transaction_started) { int code = ctx->app->db_commit(ctx); if (code) { - if (code == -1) + if (ctx->client) + release_client(ctx->client); + + if (code == -1) { + // This case is for a serialization failure, which is not really an "error." + // The transaction will restart, so we should rollback any transactionals + // that triggered above. + + for (i = ctx->used_transactionals-1; i >= 0; --i) + if (ctx->transactionals[i].rollback != NULL) + ctx->transactionals[i].rollback(ctx->transactionals[i].data); + + for (i = ctx->used_transactionals-1; i >= 0; --i) + if (ctx->transactionals[i].free) + ctx->transactionals[i].free(ctx->transactionals[i].data, 1); + return 1; + } for (i = ctx->used_transactionals-1; i >= 0; --i) - if (ctx->transactionals[i].free) - ctx->transactionals[i].free(ctx->transactionals[i].data, 0); + if (ctx->transactionals[i].free) + ctx->transactionals[i].free(ctx->transactionals[i].data, 0); uw_set_error_message(ctx, "Error running SQL COMMIT"); return 0; } } + for (i = ctx->used_transactionals-1; i >= 0; --i) + if (ctx->transactionals[i].rollback == NULL) + if (ctx->transactionals[i].commit) { + ctx->transactionals[i].commit(ctx->transactionals[i].data); + if (uw_has_error(ctx)) { + if (ctx->client) + release_client(ctx->client); + + for (i = ctx->used_transactionals-1; i >= 0; --i) + if (ctx->transactionals[i].rollback != NULL) + ctx->transactionals[i].rollback(ctx->transactionals[i].data); + + for (i = ctx->used_transactionals-1; i >= 0; --i) + if (ctx->transactionals[i].free) + ctx->transactionals[i].free(ctx->transactionals[i].data, 0); + + return 0; + } + } + for (i = 0; i < ctx->used_deltas; ++i) { delta *d = &ctx->deltas[i]; client *c = find_client(d->client); |