1. A computer program product for inserting code into a running thread of execution, the computer program product comprising: one or more computer-readable storage media and program instructions stored on the one or more computer-readable storage media, the program instructions comprising: program instructions to set a first one or more bits to a first value, wherein the first value indicates that a first set of instructions should be inserted onto a stack of a thread; program instructions to set a second one or more bits to a second value, wherein the second value indicates that no set of instructions should be inserted onto the stack until the second one or more bits is set to a third value; program instructions to execute a second set of instructions associated with a first safepoint, wherein the second set of instructions comprises one or more instructions to determine if the first one or more bits is set to the first value; program instructions to determine that the first one or more bits is set to the first value; program instructions to set a third one or more bits to a fourth value, wherein the fourth value indicates that the first set of instructions should be inserted onto the stack, based at least in part on execution of a third set of instructions associated with a second safepoint; program instructions to set the second one or more bits to the third value, wherein the third value indicates that the thread can safely execute the third set of instructions associated with the second safepoint and insert the first set of instructions onto the stack; program instructions to execute the third set of instructions associated with the second safepoint; and program instructions to insert the first set of instructions onto the stack.