Timeouts

[davidchisnall]

Is there a way of making microvium abort execution after executing a certain number of bytecodes? Currently, an infinite loop in my demo can freeze the system. Is there a way of asking Microvium to bail out after executing n bytecodes or poll some a global that we can use to set a flag from another thread?)

[coder-mike]

Yeah, I can add that functionality. It sounds useful in general and fits with the use case of running sandboxed scripts using Microvium. Would these API methods work for you:

/**
 * mvm_stopAfterNInstructions
 *
 * Set's the VM to stop (return error MVM_E_INSTRUCTION_COUNT_REACHED) after n
 * further bytecode instructions have been executed. This may help the host to
 * catch run-away VMs or infinite loops. Use n = -1 to disable the limit.
 *
 * If `n` is zero, the VM will stop before executing any further instructions.
 *
 * When the VM reaches the stopped state, further calls to the VM will fail with
 * the same error until `mvm_stopAfterNInstructions` is called again to reset
 * the countdown.
 *
 * The stopping unwinds the current call stack in a similar way to an exception,
 * except that it will not hit any catch blocks. However, be aware that if the
 * call to the VM is reentrant (e.g. the host calls the VM which calls the host
 * which calls the VM again), the stopping will only unwind the innermost call
 * stack. The outer call stack will then unwind if the inner host function
 * returns an error code (e.g. propagating the MVM_E_INSTRUCTION_COUNT_REACHED)
 * or simply does not reset the countdown, so that the VM will fail again when
 * the host returns control to the VM.
 */
MVM_EXPORT void mvm_stopAfterNInstructions(mvm_VM* vm, int32_t n);

/**
 * mvm_getInstructionCountRemaining
 *
 * If `mvm_stopAfterNInstructions` has been used to set a limit on the number of
 * instructions to execute, this function can be used to see the remaining
 * number of instructions before the VM will stop.
 *
 * The return value will be negative if the countdown is currently disabled.
 */
MVM_EXPORT int32_t mvm_getInstructionCountRemaining(mvm_VM* vm);

[coder-mike]

I've added it behind the flag #define MVM_GAS_COUNTER.

I've opened a PR for it in case you want to give any feedback before I merge into main.