dsync: Add per-mailbox sync lock that is always used. Both importing and exporting gets the lock before they even sync the mailbox. The lock is kept until the import/export finishes. This guarantees that no matter how dsync is run, two dsyncs can't be working on the same mailbox at the same time. This lock is in addition to the optional per-user lock enabled by the -l parameter. If the -l parameter is used, the same lock timeout is used for the per-mailbox lock. Otherwise 30s timeout is used. This should help to avoid email duplication when replication is enabled for public namespaces, and maybe in some other rare situations as well.

#ifndef ANVIL_CONNECTION_H
#define ANVIL_CONNECTION_H

struct anvil_connection *
anvil_connection_create(int fd, bool master, bool fifo);
void anvil_connection_destroy(struct anvil_connection *conn);

void anvil_connections_destroy_all(void);

#endif