jsonrpc_session_recv_wait(idl->session);
}
-/* Returns a number that represents the state of 'idl'. When 'idl' is updated
- * (by ovsdb_idl_run()), the return value changes. */
+/* Returns a "sequence number" that represents the state of 'idl'. When
+ * ovsdb_idl_run() changes the database, the sequence number changes. The
+ * initial fetch of the entire contents of the remote database is considered to
+ * be one kind of change. Successfully acquiring a lock, if one has been
+ * configured with ovsdb_idl_set_lock(), is also considered to be a change.
+ *
+ * As long as the sequence number does not change, the client may continue to
+ * use any data structures it obtains from 'idl'. But when it changes, the
+ * client must not access any of these data structures again, because they
+ * could have freed or reused for other purposes.
+ *
+ * The sequence number can occasionally change even if the database does not.
+ * This happens if the connection to the database drops and reconnects, which
+ * causes the database contents to be reloaded even if they didn't change. (It
+ * could also happen if the database server sends out a "change" that reflects
+ * what the IDL already thought was in the database. The database server is
+ * not supposed to do that, but bugs could in theory cause it to do so.) */
unsigned int
ovsdb_idl_get_seqno(const struct ovsdb_idl *idl)
{
return &idl->tables[table_class - idl->class->tables];
}
+/* Called by ovsdb-idlc generated code. */
struct ovsdb_idl_row *
ovsdb_idl_get_row_arc(struct ovsdb_idl_row *src,
struct ovsdb_idl_table_class *dst_table_class,
}
}
+/* Searches 'tc''s table in 'idl' for a row with UUID 'uuid'. Returns a
+ * pointer to the row if there is one, otherwise a null pointer. */
const struct ovsdb_idl_row *
ovsdb_idl_get_row_for_uuid(const struct ovsdb_idl *idl,
const struct ovsdb_idl_table_class *tc,
return NULL;
}
+/* Returns a row in 'table_class''s table in 'idl', or a null pointer if that
+ * table is empty.
+ *
+ * Database tables are internally maintained as hash tables, so adding or
+ * removing rows while traversing the same table can cause some rows to be
+ * visited twice or not at apply. */
const struct ovsdb_idl_row *
ovsdb_idl_first_row(const struct ovsdb_idl *idl,
const struct ovsdb_idl_table_class *table_class)
return next_real_row(table, hmap_first(&table->rows));
}
+/* Returns a row following 'row' within its table, or a null pointer if 'row'
+ * is the last row in its table. */
const struct ovsdb_idl_row *
ovsdb_idl_next_row(const struct ovsdb_idl_row *row)
{
static void ovsdb_idl_txn_complete(struct ovsdb_idl_txn *txn,
enum ovsdb_idl_txn_status);
+/* Returns a string representation of 'status'. The caller must not modify or
+ * free the returned string.
+ *
+ * The return value is probably useful only for debug log messages and unit
+ * tests. */
const char *
ovsdb_idl_txn_status_to_string(enum ovsdb_idl_txn_status status)
{
return "<unknown>";
}
+/* Starts a new transaction on 'idl'. A given ovsdb_idl may only have a single
+ * active transaction at a time. See the large comment in ovsdb-idl.h for
+ * general information on transactions. */
struct ovsdb_idl_txn *
ovsdb_idl_txn_create(struct ovsdb_idl *idl)
{
va_end(args);
}
+/* Marks 'txn' as a transaction that will not actually modify the database. In
+ * almost every way, the transaction is treated like other transactions. It
+ * must be committed or aborted like other transactions, it will be sent to the
+ * database server like other transactions, and so on. The only difference is
+ * that the operations sent to the database server will include, as the last
+ * step, an "abort" operation, so that any changes made by the transaction will
+ * not actually take effect. */
void
ovsdb_idl_txn_set_dry_run(struct ovsdb_idl_txn *txn)
{
txn->inc_row = row->uuid;
}
+/* Destroys 'txn' and frees all associated memory. If ovsdb_idl_txn_commit()
+ * has been called for 'txn' but the commit is still incomplete (that is, the
+ * last call returned TXN_INCOMPLETE) then the transaction may or may not still
+ * end up committing at the database server, but the client will not be able to
+ * get any further status information back. */
void
ovsdb_idl_txn_destroy(struct ovsdb_idl_txn *txn)
{
free(txn);
}
+/* Causes poll_block() to wake up if 'txn' has completed committing. */
void
ovsdb_idl_txn_wait(const struct ovsdb_idl_txn *txn)
{
hmap_init(&txn->txn_rows);
}
+/* Attempts to commit 'txn'. Returns the status of the commit operation, one
+ * of the following TXN_* constants:
+ *
+ * TXN_INCOMPLETE:
+ *
+ * The transaction is in progress, but not yet complete. The caller
+ * should call again later, after calling ovsdb_idl_run() to let the IDL
+ * do OVSDB protocol processing.
+ *
+ * TXN_UNCHANGED:
+ *
+ * The transaction is complete. (It didn't actually change the database,
+ * so the IDL didn't send any request to the database server.)
+ *
+ * TXN_ABORTED:
+ *
+ * The caller previously called ovsdb_idl_txn_abort().
+ *
+ * TXN_SUCCESS:
+ *
+ * The transaction was successful. The update made by the transaction
+ * (and possibly other changes made by other database clients) should
+ * already be visible in the IDL.
+ *
+ * TXN_TRY_AGAIN:
+ *
+ * The transaction failed for some transient reason, e.g. because a
+ * "verify" operation reported an inconsistency or due to a network
+ * problem. The caller should wait for a change to the database, then
+ * compose a new transaction, and commit the new transaction.
+ *
+ * Use the return value of ovsdb_idl_get_seqno() to wait for a change in
+ * the database. It is important to use its return value *before* the
+ * initial call to ovsdb_idl_txn_commit() as the baseline for this
+ * purpose, because the change that one should wait for can happen after
+ * the initial call but before the call that returns TXN_TRY_AGAIN, and
+ * using some other baseline value in that situation could cause an
+ * indefinite wait if the database rarely changes.
+ *
+ * TXN_NOT_LOCKED:
+ *
+ * The transaction failed because the IDL has been configured to require
+ * a database lock (with ovsdb_idl_set_lock()) but didn't get it yet or
+ * has already lost it.
+ *
+ * Committing a transaction rolls back all of the changes that it made to the
+ * IDL's copy of the database. If the transaction commits successfully, then
+ * the database server will send an update and, thus, the IDL will be updated
+ * with the committed changes. */
enum ovsdb_idl_txn_status
ovsdb_idl_txn_commit(struct ovsdb_idl_txn *txn)
{
/* Attempts to commit 'txn', blocking until the commit either succeeds or
* fails. Returns the final commit status, which may be any TXN_* value other
- * than TXN_INCOMPLETE. */
+ * than TXN_INCOMPLETE.
+ *
+ * This function calls ovsdb_idl_run() on 'txn''s IDL, so it may cause the
+ * return value of ovsdb_idl_get_seqno() to change. */
enum ovsdb_idl_txn_status
ovsdb_idl_txn_commit_block(struct ovsdb_idl_txn *txn)
{
return status;
}
+/* Returns the final (incremented) value of the column in 'txn' that was set to
+ * be incremented by ovsdb_idl_txn_increment(). 'txn' must have committed
+ * successfully. */
int64_t
ovsdb_idl_txn_get_increment_new_value(const struct ovsdb_idl_txn *txn)
{
return txn->inc_new_value;
}
+/* Aborts 'txn' without sending it to the database server. This is effective
+ * only if ovsdb_idl_txn_commit() has not yet been called for 'txn'.
+ * Otherwise, it has no effect.
+ *
+ * Aborting a transaction doesn't free its memory. Use
+ * ovsdb_idl_txn_destroy() to do that. */
void
ovsdb_idl_txn_abort(struct ovsdb_idl_txn *txn)
{
}
}
+/* Returns a string that reports the error status for 'txn'. The caller must
+ * not modify or free the returned string. A call to ovsdb_idl_txn_destroy()
+ * for 'txn' may free the returned string.
+ *
+ * The return value is ordinarily one of the strings that
+ * ovsdb_idl_txn_status_to_string() would return, but if the transaction failed
+ * due to an error reported by the database server, the return value is that
+ * error. */
const char *
ovsdb_idl_txn_get_error(const struct ovsdb_idl_txn *txn)
{
return true;
}
+/* Returns the transaction currently active for 'row''s IDL. A transaction
+ * must currently be active. */
struct ovsdb_idl_txn *
ovsdb_idl_txn_get(const struct ovsdb_idl_row *row)
{
return txn;
}
+/* Returns the IDL on which 'txn' acts. */
struct ovsdb_idl *
ovsdb_idl_txn_get_idl (struct ovsdb_idl_txn *txn)
{
bool ovsdb_idl_row_is_synthetic(const struct ovsdb_idl_row *);
\f
-/* Transactions. */
+/* Transactions.
+ *
+ * A transaction may modify the contents of a database by modifying the values
+ * of columns, deleting rows, inserting rows, or adding checks that columns in
+ * the database have not changed ("verify" operations), through
+ * ovsdb_idl_txn_*() functions. (The OVSDB IDL code generator produces helper
+ * functions that internally call the ovsdb_idl_txn_*() functions. These are
+ * likely to be more convenient.)
+ *
+ * Reading and writing columns and inserting and deleting rows are all
+ * straightforward. The reasons to verify columns are less obvious.
+ * Verification is the key to maintaining transactional integrity. Because
+ * OVSDB handles multiple clients, it can happen that between the time that
+ * OVSDB client A reads a column and writes a new value, OVSDB client B has
+ * written that column. Client A's write should not ordinarily overwrite
+ * client B's, especially if the column in question is a "map" column that
+ * contains several more or less independent data items. If client A adds a
+ * "verify" operation before it writes the column, then the transaction fails
+ * in case client B modifies it first. Client A will then see the new value of
+ * the column and compose a new transaction based on the new contents written
+ * by client B.
+ *
+ * When a transaction is complete, which must be before the next call to
+ * ovsdb_idl_run() on 'idl', call ovsdb_idl_txn_commit() or
+ * ovsdb_idl_txn_abort().
+ *
+ * The life-cycle of a transaction looks like this:
+ *
+ * 1. Create the transaction and record the initial sequence number:
+ *
+ * seqno = ovsdb_idl_get_seqno(idl);
+ * txn = ovsdb_idl_txn_create(idl);
+ *
+ * 2. Modify the database with ovsdb_idl_txn_*() functions directly or
+ * indirectly.
+ *
+ * 3. Commit the transaction by calling ovsdb_idl_txn_commit(). The first call
+ * to this function probably returns TXN_INCOMPLETE. The client must keep
+ * calling again along as this remains true, calling ovsdb_idl_run() in
+ * between to let the IDL do protocol processing. (If the client doesn't
+ * have anything else to do in the meantime, it can use
+ * ovsdb_idl_txn_commit_block() to avoid having to loop itself.)
+ *
+ * 4. If the final status is TXN_TRY_AGAIN, wait for ovsdb_idl_get_seqno() to
+ * change from the saved 'seqno' (it's possible that it's already changed,
+ * in which case the client should not wait at all), then start over from
+ * step 1. Only a call to ovsdb_idl_run() will change the return value of
+ * ovsdb_idl_get_seqno(). (ovsdb_idl_txn_commit_block() calls
+ * ovsdb_idl_run().)
+ */
enum ovsdb_idl_txn_status {
TXN_UNCOMMITTED, /* Not yet committed or aborted. */
'rows' map values. Refer to Row for more details.
- 'change_seqno': A number that represents the IDL's state. When the IDL
- is updated (by Idl.run()), its value changes.
+ is updated (by Idl.run()), its value changes. The sequence number can
+ occasionally change even if the database does not. This happens if the
+ connection to the database drops and reconnects, which causes the
+ database contents to be reloaded even if they didn't change. (It could
+ also happen if the database server sends out a "change" that reflects
+ what the IDL already thought was in the database. The database server is
+ not supposed to do that, but bugs could in theory cause it to do so.)
- 'lock_name': The name of the lock configured with Idl.set_lock(), or None
if no lock is configured.
class Transaction(object):
+ """A transaction may modify the contents of a database by modifying the
+ values of columns, deleting rows, inserting rows, or adding checks that
+ columns in the database have not changed ("verify" operations), through
+ Row methods.
+
+ Reading and writing columns and inserting and deleting rows are all
+ straightforward. The reasons to verify columns are less obvious.
+ Verification is the key to maintaining transactional integrity. Because
+ OVSDB handles multiple clients, it can happen that between the time that
+ OVSDB client A reads a column and writes a new value, OVSDB client B has
+ written that column. Client A's write should not ordinarily overwrite
+ client B's, especially if the column in question is a "map" column that
+ contains several more or less independent data items. If client A adds a
+ "verify" operation before it writes the column, then the transaction fails
+ in case client B modifies it first. Client A will then see the new value
+ of the column and compose a new transaction based on the new contents
+ written by client B.
+
+ When a transaction is complete, which must be before the next call to
+ Idl.run(), call Transaction.commit() or Transaction.abort().
+
+ The life-cycle of a transaction looks like this:
+
+ 1. Create the transaction and record the initial sequence number:
+
+ seqno = idl.change_seqno(idl)
+ txn = Transaction(idl)
+
+ 2. Modify the database with Row and Transaction methods.
+
+ 3. Commit the transaction by calling Transaction.commit(). The first call
+ to this function probably returns Transaction.INCOMPLETE. The client
+ must keep calling again along as this remains true, calling Idl.run() in
+ between to let the IDL do protocol processing. (If the client doesn't
+ have anything else to do in the meantime, it can use
+ Transaction.commit_block() to avoid having to loop itself.)
+
+ 4. If the final status is Transaction.TRY_AGAIN, wait for Idl.change_seqno
+ to change from the saved 'seqno' (it's possible that it's already
+ changed, in which case the client should not wait at all), then start
+ over from step 1. Only a call to Idl.run() will change the return value
+ of Idl.change_seqno. (Transaction.commit_block() calls Idl.run().)"""
+
# Status values that Transaction.commit() can return.
UNCOMMITTED = "uncommitted" # Not yet committed or aborted.
UNCHANGED = "unchanged" # Transaction didn't include any changes.
self._comments.append(comment)
def wait(self, poller):
+ """Causes poll_block() to wake up if this transaction has completed
+ committing."""
if self._status not in (Transaction.UNCOMMITTED,
Transaction.INCOMPLETE):
poller.immediate_wake()
self._txn_rows = {}
def commit(self):
- """Attempts to commit this transaction and returns the status of the
- commit operation, one of the constants declared as class attributes.
- If the return value is Transaction.INCOMPLETE, then the transaction is
- not yet complete and the caller should try calling again later, after
- calling Idl.run() to run the Idl.
+ """Attempts to commit 'txn'. Returns the status of the commit
+ operation, one of the following constants:
+
+ Transaction.INCOMPLETE:
+
+ The transaction is in progress, but not yet complete. The caller
+ should call again later, after calling Idl.run() to let the
+ IDL do OVSDB protocol processing.
+
+ Transaction.UNCHANGED:
+
+ The transaction is complete. (It didn't actually change the
+ database, so the IDL didn't send any request to the database
+ server.)
+
+ Transaction.ABORTED:
+
+ The caller previously called Transaction.abort().
+
+ Transaction.SUCCESS:
+
+ The transaction was successful. The update made by the
+ transaction (and possibly other changes made by other database
+ clients) should already be visible in the IDL.
+
+ Transaction.TRY_AGAIN:
+
+ The transaction failed for some transient reason, e.g. because a
+ "verify" operation reported an inconsistency or due to a network
+ problem. The caller should wait for a change to the database,
+ then compose a new transaction, and commit the new transaction.
+
+ Use Idl.change_seqno to wait for a change in the database. It is
+ important to use its value *before* the initial call to
+ Transaction.commit() as the baseline for this purpose, because
+ the change that one should wait for can happen after the initial
+ call but before the call that returns Transaction.TRY_AGAIN, and
+ using some other baseline value in that situation could cause an
+ indefinite wait if the database rarely changes.
+
+ Transaction.NOT_LOCKED:
+
+ The transaction failed because the IDL has been configured to
+ require a database lock (with Idl.set_lock()) but didn't
+ get it yet or has already lost it.
Committing a transaction rolls back all of the changes that it made to
- the Idl's copy of the database. If the transaction commits
+ the IDL's copy of the database. If the transaction commits
successfully, then the database server will send an update and, thus,
- the Idl will be updated with the committed changes."""
+ the IDL will be updated with the committed changes."""
# The status can only change if we're the active transaction.
# (Otherwise, our status will change only in Idl.run().)
if self != self.idl.txn:
return self._status
def commit_block(self):
+ """Attempts to commit this transaction, blocking until the commit
+ either succeeds or fails. Returns the final commit status, which may
+ be any Transaction.* value other than Transaction.INCOMPLETE.
+
+ This function calls Idl.run() on this transaction'ss IDL, so it may
+ cause Idl.change_seqno to change."""
while True:
status = self.commit()
if status != Transaction.INCOMPLETE:
poller.block()
def get_increment_new_value(self):
+ """Returns the final (incremented) value of the column in this
+ transaction that was set to be incremented by Row.increment. This
+ transaction must have committed successfully."""
assert self._status == Transaction.SUCCESS
return self._inc_new_value
projects / openvswitch / commitdiff