set @start_value = @@wsrep_slave_threads;
set @@global.wsrep_slave_threads=1;
set @@global.wsrep_slave_threads=4;
show warnings;
Level	Code	Message
set @@global.wsrep_slave_threads=0;
Warnings:
Warning	1292	Truncated incorrect wsrep_slave_threads value: '0'
show warnings;
Level	Code	Message
Warning	1292	Truncated incorrect wsrep_slave_threads value: '0'
set @@global.wsrep_slave_threads=-1;
Warnings:
Warning	1292	Truncated incorrect wsrep_slave_threads value: '-1'
show warnings;
Level	Code	Message
Warning	1292	Truncated incorrect wsrep_slave_threads value: '-1'
SET @@global.wsrep_slave_threads = r;
ERROR 42000: Incorrect argument type to variable 'wsrep_slave_threads'
set @@global.wsrep_slave_threads = @start_value;