What can “new_handler” be used for in C++ besides garbage collection?

Question

C++ programs can define and set a new_handler() that should be called from memory allocation functions like operator new() if it\'s impossible to a

Answer 1

I've never used it for anything - too many OS will grant virtual memory and SIGSEGV or similar if they can't provide it later so it's not a good idea to make a system that relies on being memory-exhaustion tolerant: it's often outside C++'s hands. Still, if you developed for a system where it could/must be relied upon, I can easily imagine a situation where some real-time data was being streamed into a queue in your process, and you were processing it and writing/sending out results as fast as you could (e.g. video hardware streaming video for recompression to disk/network). If you got to the stage where you couldn't store any more, you'd simply have to drop some, but how would you know when it got that bad? Setting an arbitrary limit would be kind of silly, especially if your software was for an embedded environment / box that only existed to do this task. And, you probably shouldn't use a function like this casually on a system with any kind of hard-disk based swap memory, as if you're already into swap you're throughput rates would be miserable ever after. But - past the caveats - it might be useful to drop packets for a while until you catch up. Perhaps dropping every Nth frame through the queued buffer would be less visible than dropping a chunk at the back or front of the queue. Whatever, discarding data from the queue could be a sane application-level use (as distinct from intra-memory-subsystem) for something like this....