Link Search Menu Expand Document

Periodic task API

Related ticket(s):

Problem Statement

SSSD contains several periodic tasks that implements custom periodic API. These APIs are more or less sophisticated but it does the same thing.

Current periodic tasks are:

  • Enumeration
  • Dynamic DNS updates
  • SUDO - full and smart refresh
  • Refresh of expired NSS entries

We want to replace these individual implementation with one back end wise API.

Implementation details

New error code:
- ERR_STOP_PERIODIC_TASK

struct be_ptask;

typedef struct tevent_req *
(*be_ptask_send_t)(TALLOC_CTX *mem_ctx,
                    struct be_ctx *be_ctx,
                    struct be_ptask *be_ptask,
                    void *pvt);

typedef errno_t
(*be_ptask_recv_t)(struct tevent_req *req);

enum be_ptask_offline {
    BE_PTASK_OFFLINE_SKIP,
    BE_PTASK_OFFLINE_DISABLE,
    BE_PTASK_OFFLINE_EXECUTE
};

errno_t be_ptask_create(TALLOC_CTX *mem_ctx,
                        struct be_ctx *be_ctx,
                        time_t period,
                        time_t first_delay,
                        time_t enabled_delay,
                        time_t timeout,
                        enum be_ptask_offline offline,
                        be_ptask_send_t send,
                        be_ptask_recv_t recv,
                        void *pvt,
                        const char *name,
                        struct be_ptask **_task);

void be_ptask_enable(struct be_ptask *task);
void be_ptask_disable(struct be_ptask *task);
void be_ptask_destroy(struct be_ptask **task);

Terminology

  • task: object of type be_ptask
  • request: tevent request that is fired periodically and is managed by task

API

  • struct be_ptask_task is encapsulated.
  • be_ptask_create() creates and starts new periodic task
  • be_ptask_enable(task) enable task and schedule next execution enabled_delay from now
  • be_ptask_disable(task) disable task, cancel current timer and wait until it is enabled again
  • be_ptask_destroy(task) destroys task and sets it to NULL

Schedule rules

  • the first execution is scheduled first_delay seconds after the task is created
  • if request returns EOK, it will be scheduled again to ‘last_execution_time + period’
  • if request returns ERR_STOP_PERIODIC_TASK, the task will be terminated
  • if request returns other error code (i.e. non fatal failure), it will be rescheduled to ‘now + period’
  • if request does not complete in timeout seconds, it will be cancelled and rescheduled to ‘now + period’
  • if the task is reenabled, it will be scheduled again to ‘now + enabled_delay’

When offline

Offline behaviour is controlled by offline parameter.

  • If offline is BE_PTASK_OFFLINE_EXECUTE and back end is offline, current request will be executed as planned.
  • If offline is BE_PTASK_OFFLINE_SKIP and back end is offline, current request will be skipped and rescheduled to ‘now + period’.
  • If offline is BE_PTASK_OFFLINE_DISABLE, an offline and online callback is registered. The task is disabled immediately when back end goes offline and then enabled again when back end goes back online.

Debugging

Task will provide enough debugging information so we can know exactly when a task is created and destroy, when it is executed and finished and when it will be executed in the future.

Author(s)

Pavel Březina <pbrezina@redhat.com>