Method and apparatus for activating/deactivating run-time determined software routines in Java compiled bytecode applications
View Patent ↗Provided is a JIT compiler that changes the status of run-time determined software routines between being activated and deactivated in an application program. Conditional statements which are used at run-time to determine whether such a routine has been activated or deactivated are presented as discrete conditions that always evaluate to a known result by using an invariant flag in the compiled bytecode. The JIT compiler optimises an application program by excluding discrete condition checks. Consequently, if the branch of the discrete condition that will never execute includes a run-time determined software routine, then the routine will be excluded from the JIT compilation and will not form part of the JIT compiled native machine code. A run-time class or code replacement facility is used as a means of activating or deactivating a run-time determined software routine at run-time by changing the value of the invariant flag of said routine.
1. A method of changing a status of a run-time determined software routine between activated and deactivated, comprising:
employing an invariant flag to evaluate a conditional statement associated with said run-time determined software routine to determine the status as one of activated or deactivated, said invariant flag being selected to cause said conditional statement to always evaluate to a known result; and
during run-time, utilising a run-time code replacement facility to change said invariant flag to a second invariant flag that causes said conditional statement to always evaluate to a different known result; and
optimizing said run-time determined software routine by excluding from compiled native machine code the run-time determined software routine when the invariant flag is selected to cause the conditional statement associated with said routine to evaluate to the different know result.
2. A method as claimed in claim 1 , wherein the invariant flag comprises one of a final static Boolean parameter, a numerical test on an invariant held and a hard coded statement and wherein said step of utilising a run-time code replacement facility to change said invariant flag comprises changing a value of the Boolean parameter, changing the invariant field or replacing the hard coded statement by its converse.
3. A method as claimed in 2 , wherein said final static Boolean parameter comprises a final static Boolean data type.
4. A method as claimed in claim 1 , wherein said run-time determined software routine comprises a class file.
5. A method as claimed in claim 4 , wherein it includes the step of just-in-time (JIT) compiling methods of the class file.
6. A method as claimed in claim 5 , wherein a interpreter maintains a method invocation count for each method of the class file and wherein the method includes the step of JIT compiling only those methods whose invocation count exceeds a threshold value.
7. A virtual machine (VM), stored on a memory for execution on a processor, arranged to carry out the method of changing a status of a runtime determined software routine between activated and deactivated, the VM being configured for:
employing an invariant flag to evaluate a conditional statement associated with said run-time determined software routine to determine its status as one of activated or deactivated, said invariant flag being selected to cause said conditional statement to always evaluate to a known result; and
during run-time, utilising a run-time code replacement facility to change said invariant flag to a second invariant flag that causes said conditional statement to always evaluate to a different known result; and
optimizing said run-time determined software routine by excluding from compiled native machine code the run-time determined software routine when the invariant flag is selected to cause the conditional statement associated with said routine to evaluate to the different known result.
8. A just-in-time (JIT) compiler, stored on a memory and executed on a processor, arranged to carry out the method of changing a status of a run-time determined software routine between activated and deactivated, the method comprising:
employing an invariant flag to evaluate a conditional statement associated with said run-time determined software routine to determine its status as one of activated or deactivated, said invariant flag being selected to cause said conditional statement to always evaluate to a known result; and
during run-time, utilising a run-time code replacement facility to change said invariant flag to a second invariant flag that causes said conditional statement to always evaluate to a different known result; and
optimizing said run-time determined software routine by excluding from compiled native machine code the run-time determined software routine when the invariant flag is selected to cause the conditional statement associated with said routine to evaluate to the different known result.
9. A computer program product in a computer readable medium for carrying out the method of changing a status of a run-time determined software routine between activated and deactivated, said method comprising:
employing an invariant flag to evaluate a conditional statement associated with said run-time determined software routine to determine the status as one of activated or deactivated, said invariant flag being selected to cause said conditional statement to always evaluate to a known result; and
during run-time, utilising a run-time code replacement facility to change said invariant flag to a second invariant flag that cause said conditional statement to evaluate to a different known result; and
optimizing said run-time determined software routine by excluding from compiled native machine code the run-time determined software routine when the invariant flag is selected to cause the conditional statement associated with said routine to evaluate to the different known result.