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 CONNECT_LIMIT_H
#define CONNECT_LIMIT_H

struct connect_limit *connect_limit_init(void);
void connect_limit_deinit(struct connect_limit **limit);

unsigned int connect_limit_lookup(struct connect_limit *limit,
				  const char *ident);
void connect_limit_connect(struct connect_limit *limit, pid_t pid,
			   const char *ident);
void connect_limit_disconnect(struct connect_limit *limit, pid_t pid,
			      const char *ident);
void connect_limit_disconnect_pid(struct connect_limit *limit, pid_t pid);
void connect_limit_dump(struct connect_limit *limit, struct ostream *output);

#endif