Redis Lists: BLPOP

BLPOP key1 [key2 ] timeout

Redis BLPOP command is used to blocks the connection when there are no elements to pop from any of the given lists or remove and get the first element in a list if available. An element is popped from the head of the first list that is non-empty.

Syntax:

BLPOP LIST1 LIST2 .. LISTN TIMEOUT    

Available since

2.0.0.

Return Value

String reply, value of element stored at key or nil

Return Value Type

String

Example: Redis BLPOP

127.0.0.1:6379> RPUSH mycolor1 R G B
(integer) 3
127.0.0.1:6379> RPUSH mycolor2 Y O P
(integer) 3
127.0.0.1:6379> BLPOP mycolor mycolor1 mycolor2 30
1) "mycolor1"
2) "R"
127.0.0.1:6379> BLPOP mycolor mycolor1 mycolor2 30
1) "mycolor1"
2) "G"
127.0.0.1:6379> BLPOP mycolor mycolor1 mycolor2 30
1) "mycolor1"
2) "B"
127.0.0.1:6379> BLPOP mycolor mycolor1 mycolor2 30
1) "mycolor2"
2) "Y"
127.0.0.1:6379> BLPOP mycolor mycolor1 mycolor2 30
1) "mycolor2"
2) "O"
127.0.0.1:6379> BLPOP mycolor mycolor1 mycolor2 30
1) "mycolor2"
2) "P"
127.0.0.1:6379> BLPOP  mycolor mycolor1 mycolor2 30
(nil)
(30.03s)

Above example will block the client for 30 seconds to execute any command. If any data comes in the specified key lists then it returns otherwise after 30 seconds nil value is returned.

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