1. A non-transitory computer readable medium having computer executable instructions for implementing a method of deterministic replay of a computer program, the method comprising: periodically taking a snapshot of the computer program; returning to a state in the history of execution of the program, the state comprising a set of values of: registers of a processor on which the program is running, working memory space to which the program has access and operating system resources allocated to the program; identifying in machine code representing the program, instances of machine code instructions for a first process that accesses the portion of shared memory; identifying a second process that accesses the portion of shared memory; storing an indication of ownership of the portion of memory by the first process in a first execution log associated with the first process; modifying the program machine code such that the first processes has read and write permission to access the portion of shared memory and the second processes has neither read nor write permission to access the shared portion of memory; identifying during concurrent execution of the first and second processes when the second process attempts to access the portion of shared memory; and executing an instruction sequence in response to identifying of said attempt to: modify the program machine code in order that the second process has read and write permission to access the shared portion of memory; store an indication of ownership of the portion of memory by the second process in a second execution log; recording data and event to enable asynchronous modification of a shared portion of memory by the first process and second process and deterministically replaying the program using recorded log event at the appropriate time.