A method of converting a program code of a program running in multi-thread to a program code which causes fewer lock collisions. The method includes reading the program code into a memory and searching the program code for a first conditional statement making a branch to a path, which is in a synchronized block and has no side effect on the synchronized block; duplicating the path having no side effect to which the branch is made by the searched first conditional statement into the outside of the synchronized block; and adding a second conditional statement into the program code in response to the duplication, wherein the second conditional statement is a conditional statement making a branch to the duplicated path having no side effect. Also provided is a system and an article of manufacture which causes a computer to carry out the steps of the above method.