tiny.mprompt.Prompt

1/// The runtime's record for one prompt: its stacklet, its links to other prompts, its reference2/// count, and the registers saved for its entry and its last suspend. A prompt marks the point3/// where code entered its stacklet, and that code can later suspend back to it. A body receives a4/// `*Prompt` for the stacklet it runs on, and `yieldPrompt` takes that pointer as the point to5/// suspend back to. The runtime reads and writes every field, and callers pass the pointer through.6/// A prompt is entered once, and `promptEnter` asserts that it is neither a prompt whose code or7/// nested code runs on this thread (active prompt) nor a suspended one. The runtime frees the8/// record, or keeps it for reuse, when its reference count reaches zero, so a `*Prompt` stays valid9/// only while its code runs or a resumption for it is held.10pub const Prompt = extern struct {11    /// While the prompt is active, this field holds the next active prompt outward, or null for the12    /// outermost. While the prompt is suspended, this field holds null in the prompt the code13    /// suspended to. In each prompt captured inside that one, this field holds the next prompt14    /// outward in the captured chain. While the record waits in the stack cache, this field holds15    /// the next cached record.16    parent: ?*Prompt,17    /// Holds null while the prompt is active. While the prompt is suspended, this field points to18    /// the innermost prompt of the chain captured with it. A new prompt points to itself.19    top: ?*Prompt,20    /// The number of owners of the prompt, starting at 1. Each saved stack copy adds one owner, as21    /// does each resume of a reference-counted handle resumable more than once (multi-shot handle).22    /// The runtime frees the prompt's stacklets when the count reaches zero.23    refcount: isize,24    /// The stacklet the prompt's code runs on. The runtime reserves each stacklet as a fixed-size25    /// range of address space with an unmapped gap at each end, and commits its pages as the stack26    /// grows into them. The code's type for a stacklet is `GStack`, and the runtime's fatal27    /// messages, such as "unable to reserve gstack virtual memory", call it a gstack.28    gstack: *GStack,29    /// The registers saved by the call that last entered or resumed the prompt. A suspend or a30    /// return from the prompt's code jumps there.31    return_point: ?*ReturnPoint,32    /// Registers saved at the suspend while the prompt is suspended, where a resume jumps. This33    /// field is null for a new prompt and after its code returns.34    resume_point: ?*ResumePoint,35    /// The saved stack pointer for the inactive side of the last switch, XORed with a random36    /// per-process value (guard cookie). Before each jump the runtime checks the target against it,37    /// and a mismatch stops the program with a "potential stack corruption detected" panic.38    sp: ?*anyopaque,39    /// The frame record, holding an instruction pointer, that the stack-entry code passes to the40    /// prompt's first function. The runtime stores it and reads it nowhere.41    unwind_frame: ?*UnwindFrame,42};

1pub const Prompt = raw.Prompt;