percallstack

Percallstack is a concept in programming that describes maintaining separate call stacks for individual units of work within a program, rather than using a single shared call stack per thread. In runtimes that support asynchronous execution, coroutines, or lightweight tasks, a per-call-stack architecture allows each task to suspend, resume, or unwind independently, preserving its own control-flow state without mutating a common thread stack.

Key characteristics include isolation of stack state to each task or coroutine, dynamic growth to accommodate varying depths, and the ability to switch between stacks when scheduling different tasks. This approach is often discussed in the context of stackful versus stackless coroutines, and can be realized through segmented or per-task stacks, or through runtime-managed continuations that separate logical call frames from the physical thread.

Applications and implications vary by platform. Per-call stacks can improve debugging and profiling by providing clearer task-level traces, enhance fault isolation by containing failures within a task’s stack, and support advanced scheduling strategies in asynchronous runtimes. They can also enable smaller memory footprints for many lightweight tasks, if stacks are allocated on demand.

Design considerations include memory overhead, stack growth policies, and interaction with garbage collectors, native code interfaces, and debugging tools. Challenges involve increased runtime complexity, potential performance overhead from frequent stack switching, and the need for robust unwinding and exception handling across multiple stacks.

Per-call stacks are related to broader concepts such as per-thread call stacks, stackful versus stackless coroutines, segmented stacks, and continuations. They are often discussed as an architectural option in languages and runtimes that emphasize fine-grained concurrency and isolation.