digitalmars.D.bugs - [Issue 19252] New: Templated format with variable width allocates
- d-bugmail puremagic.com (33/33) Sep 19 2018 https://issues.dlang.org/show_bug.cgi?id=19252
https://issues.dlang.org/show_bug.cgi?id=19252 Issue ID: 19252 Summary: Templated format with variable width allocates 2GB of RAM per call. Product: D Version: D2 Hardware: All OS: All Status: NEW Severity: major Priority: P1 Component: phobos Assignee: nobody puremagic.com Reporter: default_357-line yahoo.de Consider the following code: void main() { import core.memory; import std.format; import std.stdio; auto s = format!"%0*d"(0, 0); writefln!"%s, but %s"(s, GC.stats.usedSize); } Since 2.079, this will output "Success with output: 0, but 2147483680". This happens because format will preallocate an appender based on its estimate of the output string length, but guessLength does not know about spec.DYNAMIC (the representation of "*"), which is represented by int.max. So ... guessLength guesses a length of int.max plus some small fry, allocating 2GB. This does not explode on Linux because the GC uses mmap, and Linux happily lets the program overcommit and allocate terabytes of RAM, since it isn't going to be used. But it's still quite bad. Fixed by https://github.com/dlang/phobos/pull/6713 --
Sep 19 2018