BLPOP

BLPOP is the blocking form of LPOP. It checks the keys in the order given and pops the first element of the first one that holds a non-empty list. If every list is empty or missing, the connection waits until another client pushes to one of the keys, or until timeout passes.

While waiting, the client is served from whichever of its keys receives an element first. A key that changes to a different type while you wait is skipped, and the client keeps waiting.

timeout is in seconds and can have a fractional part (for example 0.5). 0 waits forever.

Inside MULTI / EXEC and inside scripts, BLPOP never waits: if no element is available it replies right away as if the timeout had expired.

Return value

Case	RESP2	RESP3
Element popped	Two-element array: the key, then the element	Same
Timeout expired	Nil array	Null

Errors:

• ERR timeout is not a float or out of range if timeout is not a number.
• ERR timeout is negative if timeout is below 0.
• ERR timeout is out of range if timeout is too large.
• WRONGTYPE if a key reached before the first non-empty list holds a value that is not a list.

Examples

127.0.0.1:6379> RPUSH jobs j1 j2
(integer) 2
127.0.0.1:6379> BLPOP empty jobs 5
1) "jobs"
2) "j1"
127.0.0.1:6379> BLPOP empty 1.5
(nil)
(1.50s)

Waiting for work in one client:

127.0.0.1:6379> BLPOP jobs:new 0

and pushing from another:

127.0.0.1:6379> RPUSH jobs:new "build-42"
(integer) 1

The first client then receives:

1) "jobs:new"
2) "build-42"

Compatibility

Same as Redis 7.4 and Valkey 8.

See also

BRPOP, LPOP, BLMPOP, BLMOVE, RPUSH