@spec delete(t(), key()) :: :ok

Deletes the item from the cache.

@spec dirty_delete(t(), key()) :: :ok

Dirty equivalent of delete/2.

@spec dirty_fetch_or_store(t(), key(), fetch_or_store_fun()) ::
  {:ok, value()} | {:error, any()}

Dirty equivalent of fetch_or_store/3.

@spec dirty_get_or_store(t(), key(), store_fun()) :: value()

Dirty equivalent of get_or_store/3.

@spec dirty_insert_new(t(), key(), store_value()) :: :ok | {:error, :already_exists}

Dirty equivalent of insert_new/3.

@spec dirty_put(t(), key(), store_value()) :: :ok

Dirty equivalent of put/3.

@spec dirty_update(t(), key(), update_fun()) :: :ok | {:error, any()}

Dirty equivalent of update/3.

@spec dirty_update_existing(t(), key(), update_fun()) ::
  :ok | {:error, :not_existing} | {:error, any()}

Dirty equivalent of update_existing/3.

@spec ets(t()) :: :ets.tab()

Returns the ets table managed by the cache.

@spec fetch_or_store(t(), key(), fetch_or_store_fun()) ::
  {:ok, value()} | {:error, any()}

Retrieves the item from the cache, or inserts the new item.

If the item exists in the cache, it is retrieved. Otherwise, the lambda function is executed and its result is stored under the given key, but only if it returns an {:ok, value} tuple. If the {:error, reason} tuple is returned, caching is not done and the error becomes the result of the function. If the lambda returns none of the above, a RuntimeError is raised.

The lambda may return either a plain value or %ConCache.Item{}.

This function is not supported by :bag and :duplicate_bag ETS tables.

Note: if the item is already in the cache, this function amounts to a simple get without any locking, so you can expect it to be fairly fast.

Emits [:con_cache, :stats, :hit] telemetry event if the item is found, and [:con_cache, :stats, :miss] otherwise.

@spec get(t(), key()) :: value()

Reads the item from the cache.

A read is always "dirty", meaning it doesn't block while someone is updating the item under the same key. A read doesn't expire TTL of the item, unless touch_on_read option is set while starting the cache.

Emits [:con_cache, :stats, :hit] telemetry event if the item is found, and [:con_cache, :stats, :miss] otherwise.

@spec get_or_store(t(), key(), store_fun()) :: value()

Retrieves the item from the cache, or inserts the new item.

If the item exists in the cache, it is retrieved. Otherwise, the lambda function is executed and its result is stored under the given key.

The lambda may return either a plain value or %ConCache.Item{}.

This function is not supported by :bag and :duplicate_bag ETS tables.

Note: if the item is already in the cache, this function amounts to a simple get without any locking, so you can expect it to be fairly fast.

Emits [:con_cache, :stats, :hit] telemetry event if the item is found, and [:con_cache, :stats, :miss] otherwise.

@spec insert_new(t(), key(), store_value()) :: :ok | {:error, :already_exists}

Inserts the item into the cache unless it exists.

@spec isolated(t(), key(), nil | pos_integer(), (-> any())) :: any()

Isolated execution over arbitrary lock in the cache.

You can do whatever you want in the function, not necessarily related to the cache. The return value is the result of the provided lambda.

This allows you to perform flexible isolation. If you use the key of your item as a key, then this operation will be exclusive to updates. This can be used e.g. to perform isolated reads:

# Process A:
ConCache.isolated(:my_cache, :my_item_key, fn() -> ... end)

# Process B:
ConCache.update(:my_cache, :my_item, fn(old_value) -> ... end)

These two operations are mutually exclusive.

@spec put(t(), key(), store_value()) :: :ok

Stores the item into the cache.

@spec size(t()) :: non_neg_integer()

Returns the number of items stored in the cache.

@spec start_link(options()) :: Supervisor.on_start()

Starts the server and creates an ETS table.

Options:

• {:name, atom} - A name of the cache process.

• {:ttl_check_interval, time_ms | false} - Required. A check interval for TTL expiry. Provide a positive integer for expiry to work, or pass false to disable ttl checks. See below for more details on expiry.

• {:global_ttl, time_ms | :infinity} - The time after which an item expires. When an item expires, it is removed from the cache. Updating the item extends its expiry time.

• {:touch_on_read, true | false} - Controls whether read operation extends expiry of items. False by default.

• {:callback, callback_fun} - If provided, this function is invoked after an item is inserted or updated, or before it is deleted.
• {:acquire_lock_timeout, timeout_ms} - The time a client process waits for the lock. Default is 5000.
• {:ets_options, [ets_option] – The options for ETS process.
• {:n_lock_partitions, pos_integer} - A positive integer representing the desired number of lock partitions

In addition, following ETS options are supported:

• :set - An ETS table will be of the :set type (default).
• :ordered_set - An ETS table will be of the :ordered_set type.
• :bag - An ETS table will be of the :bag type.
• :duplicate_bag - An ETS table will be of the :duplicate_bag type.
• :named_table
• :name
• :heir
• :write_concurrency
• :read_concurrency
• :decentralized_counters

Child specification

To insert your cache into the supervision tree, pass the child specification in the shape of {ConCache, con_cache_options}. For example:

{ConCache, [name: :my_cache, ttl_check_interval: false]}

Expiry

To configure expiry, you need to provide positive integer for the :ttl_check_interval option. This integer represents the millisecond interval in which the expiry is performed. You also need to provide the :global_ttl option, which represents the default TTL time for the item.

TTL of each item is by default extended only on modifications. This can be changed with the touch_on_read: true option.

If you need a granular control of expiry per each item, you can pass a ConCache.Item struct when storing data.

If you don't want a modification of an item to extend its TTL, you can pass a ConCache.Item struct, with :ttl field set to :no_update.

Choosing ttl_check_interval time

When expiry is configured, the owner process works in discrete steps, doing cleanups every ttl_check_interval milliseconds. This approach allows the owner process to do fairly small amount of work in each discrete step.

Assuming there's no huge system overload, an item's max lifetime is thus global_ttl + ttl_check_interval [ms], after the last item's update.

Thus, a lower value of ttl_check_interval time means more frequent purging which may reduce your memory consumption, but could also cause performance penalties. Higher values put less pressure on processing, but item expiry is less precise.

@spec touch(t(), key()) :: :ok

Manually touches the item to prolongate its expiry.

@spec try_isolated(t(), key(), nil | pos_integer(), (-> any())) ::
  {:error, :locked} | {:ok, any()}

Similar to isolated/4 except it doesn't wait for the lock to be available.

If the lock can be acquired immediately, it will be acquired and the function will be invoked. Otherwise, an error is returned immediately.

@spec update(t(), key(), update_fun()) :: :ok | {:error, any()}

Updates the item, or stores new item if it doesn't exist.

The update_fun is invoked after the item is locked. Here, you can be certain that no other process will update this item, unless they are doing dirty updates or writing directly to the underlying ETS table. This function is not supported by :bag or :duplicate_bag ETS tables.

The updater lambda must return one of the following:

• {:ok, value} - causes the value to be stored into the table
• {:error, reason} - the value won't be stored and {:error, reason} will be returned

@spec update_existing(t(), key(), update_fun()) ::
  :ok | {:error, :not_existing} | {:error, any()}

Updates the item only if it exists. Otherwise works just like update/3.