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 MAIL_COMMAND_H
#define MAIL_COMMAND_H

struct mail_command;

extern struct mail_command *stable_mail_commands_head;
extern struct mail_command *stable_mail_commands_tail;

int mail_command_update_parse(const char *const *args, const char **error_r);

void mail_command_ref(struct mail_command *cmd);
void mail_command_unref(struct mail_command **cmd);

void mail_commands_free_memory(void);
void mail_commands_init(void);
void mail_commands_deinit(void);

#endif