[concurrent programming 052] talk about double check lock and its advantages?

Talk about the double check lock and its advantages ?

The above is the correct code for double check lock . Does it look a bit like a singleton design pattern ？ But the common way of writing singleton pattern is There seems to be only one if(instance==null) The judgment of the , there if There are two judgments , This is called double checking . For locks, it's code Medium synchronized Code block . Two judgments + One synchronized= Double check lock .

Look at the advantages of double checking ： As shown in the above code , If you check it for the first time instance Not for null, Then you don't need to perform the following Lock and initial operation . therefore , Can be significantly reduced synchronized Performance overhead .