infinite loop issue on smart contract

[mjshin82]

An infinite loop occurs when using multi index table iterator.

// infinite loop! (only when table is not empty)
for (auto itr = table.cbegin(); itr != table.cend(); itr++) {
}

// no infinite loop
for (auto itr = table.cbegin(); itr != table.cend(); ++itr) {
}

Also, in case of infinite loop, the contract is not terminated (more than 0.2 seconds) and nodeos itself blocks with 99% cpu usage.

[bytemaster]

I have managed to replicate the issue....

for (auto itr = table.cbegin(); itr != table.cend(); itr++) {
      print( "*" );
}

Turns out operator++ is implemented wrong in multi_index container, it returns a copy of a temporary which is incremented rather than incrementing itself after making a copy and returning the original value.

This test will eventually exit, but it takes several seconds using binaryen before it hits the block-cpu limit. Our unit tests don't enforce a deadline and binaryen is slow processing the tight loop.

while( true ) {
   now();
}

There is a big difference in behavior between binaryen and wavm when it comes to the performance of these tight loops.

If I lower the block-cpu limit then it exits quicker without peging CPU. If you were running this in debug vs release I suspect there could be a 10x long delay which could give the perception of minutes of runtime or "infinite" for the impatient.

[mjshin82]

Thanks!
It solved