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Control whether there's a guard pattern at C stack limit
jonroach 5 Aug 2026 09:33
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11 months ago
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 #ifndef COROUTINE_H
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 #define COROUTINE_H
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 #include <stdbool.h>
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 #include <stddef.h>
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 #include <stdint.h>
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 #include "cor_platform_inc.h"
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 #include "coroutine_names_def.h"
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 ///////////////////////////////////////////////////////////////////////////////
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 // Coroutine
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 //
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 // Coroutines for C, based on setjmp/longjmp.
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 // Thread safe - each thread has its own coroutine system
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 // Coroutines are cooperatively scheduled
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 // Coroutines have their own stack (currently 16K each)
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 // A coroutine can be continued, queried, or deleted on a different thread.
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 //
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 // Usage:
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 // Coroutine_StartSystem(); // call once per thread before using coroutines
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 // Coroutine *co = Coroutine_New(start_function);
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 // void *result;
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 // if (Coroutine_Run(co, initial_value, &result)) {
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 // // Handle the failure
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 // }
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 // Coroutine_Delete(co);
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 // Coroutine_StopSystem(); // call once per thread when done with coroutines
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 //
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 // Inside the coroutine function:
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 // void *value = Coroutine_Yield(yield_value, on_yield, this);
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 // ...
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 // return return_value;
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 //
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 // To create a coroutine:
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 // Coroutine *co = Coroutine_New(start_function);
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 // To start or continue a coroutine:
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 // void *result = Coroutine_Continue(co, value, early);
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 // // early=true puts the coroutine at the head of the run queue
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 // // early=false puts the coroutine at the tail of the run queue
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 // To yield from inside a coroutine:
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 // void *value = Coroutine_Yield(yield_value, on_yield, this);
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 // // on_yield is called before the next coroutine is run
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 // // 'this' is passed to on_yield as its parameter
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 // // value is the value passed to Coroutine_Continue
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 // To delete a coroutine:
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 // Coroutine_Delete(co);
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 // To get the value yielded from, or returned by a corotuine:
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 // void *value = Coroutine_GetValue(co);
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 // To get the currently running coroutine (NULL if none):
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 // Coroutine *co = Coroutine_GetActive();
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 // To check if a coroutine is currently running:
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 // bool running = Coroutine_IsRunning(co);
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 //
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 // Notes:
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 // Coroutine is not expected to be used directly, but as a foundation for
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 // higher level constructs such as Generators, Async, etc.
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 //
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 ///////////////////////////////////////////////////////////////////////////////
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 // The stack is used as follows:
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 // +------------------+ <- stack top
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 // | coroutine header | <- more claimed as needed in Coroutine_New
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 // +------------------+ <-
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 // | coroutine stack | <-
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 // +------------------+ <-
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 // | coroutine header |
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 // +------------------+
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 // | coroutine stack |
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 // +------------------+
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 // | coroutine header |
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 // +------------------+
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 // | coroutine stack |
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 // +------------------+
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 // | coroutine header |
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 // +------------------+
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 // | coroutine stack |
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 // +------------------+
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 // | coroutine header |
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 // +------------------+
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 // | startup space | <- set aside by Coroutine_StartSystem
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 // +------------------+
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 // | caller | <- This calls Coroutine_StartSystem etc
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 // +------------------+
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 // | used stack |
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 // +------------------+ <- stack bottom
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 // Each coroutine has this much stack:
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 // For Python, we set it to 17 * (enough for a PyEval_EvalDefault), so we get at least 7
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 // calls deep before we need a new chunk, ie maximum multi-chunk wastage is under 6% address space.
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 //
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 // There's a trade-off between smaller chunk sizes, which allow more async tasks to co-exist
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 // on a thread, and larger chunk sizes which waste less memory in part-used chunks.
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 //
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 // ... which means 10000 async tasks need a 2.6 GB stack, which fits comfortably in the address map.
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 //
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 // Note, when developing the use of Coroutine in Python, the author found the following used
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 // excessive amounts of stack space:
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 // Tk_Init: on an Intel 64 bit Mac it used 72k.
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 // _decimal multplies of big decimal numbers: 256k+640 (2 x 128k buffers in squaretrans_pow2() + workings)
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 //
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 // On 64 bit macos, PYOS_STACK_MARGIN_BYTES is 2k * sizeof(void *), ie 16k, or 17 of those, 272k, should give enough slack to operate well.
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 #ifndef Coroutine_API_FUNC
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 #define Coroutine_API_FUNC(T) extern T
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 #endif
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 // No coroutine will ask for less stack than this
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 #ifndef COROUTINE_MINIMUM_STACK_SIZE
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 #define COROUTINE_MINIMUM_STACK_SIZE (4096 * sizeof(void *))
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 #endif
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 // A guard pattern is placed at the end of every stack chunk to detect stack overruns.
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 // The initial stack chunk ends at the C stack's limit, and is the only chunk not created
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 // by calling a routine and using alloca().
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 // On Windows, the OS assigns real memory pages for the used stack only (not unusual), but
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 // restricts when new pages are assigned. My guess is that it assumes read/write of an
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 // unassigned page which is also beyond the stack pointer is probably a bug. The consequence
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 // is that you can't write a guard pattern at the C stack's limit, hence this configuration
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 // control exists.
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 #ifndef COROUTINE_GUARD_AT_C_STACK_LIMIT
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 #if defined(MS_WIN32)
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 #define COROUTINE_GUARD_AT_C_STACK_LIMIT 0
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 #else
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 #define COROUTINE_GUARD_AT_C_STACK_LIMIT 1
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 #endif
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 #endif
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 // When Coroutine is started, an amount of stack is set aside to give
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 // the caller of Coroutine_StartSystem a bit of room to work before calling
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 // Coroutine_Run(), that is this amount:
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 #ifndef COROUTINE_STARTUP_STACK_SIZE
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 #ifndef _NDEBUG
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 #define COROUTINE_STARTUP_STACK_SIZE (1024 * sizeof(void *))
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 #else
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 #define COROUTINE_STARTUP_STACK_SIZE (128 * sizeof(void *))
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 #endif
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 #endif
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 // This is *expensive* to turn on, especially if you have lots of stack pieces (eg when there's lots of Tasks)
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 #ifndef COROUTINE_CHECK_INTEGRITY_ON_STACK_CHECK
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 #define COROUTINE_CHECK_INTEGRITY_ON_STACK_CHECK 0
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 #endif
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 #ifndef COROUTINE_RECORD_LOWEST_HEADROOM
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 #define COROUTINE_RECORD_LOWEST_HEADROOM 1
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 #endif
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 // Returned by Coroutine_StopSystem(), this summarises the coroutine session
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 typedef struct Coroutine_Report {
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 unsigned coroutines_created;
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 unsigned coroutines_pool_size;
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 size_t lowest_headroom;
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 size_t largest_stack;
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 } Coroutine_Report;
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 typedef enum Coroutine_Err {
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 Coroutine_OK = 0,
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 Coroutine_Err_SystemNotRunning,
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 Coroutine_Err_SystemRunning,
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 Coroutine_Err_NoStack,
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 Coroutine_Err_CoroutineFromWrongThread,
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 Coroutine_Err_ACoroutineIsAlreadyRunning,
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 Coroutine_Err_ExitWithRunningCoroutines,
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 Coroutine_Err_StackOverrun,
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 Coroutine_Err_InternalInsistency,
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 Coroutine_Err_CouldNotInitialiseSystem,
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 Coroutine_Err_WrongState,
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 Coroutine_Err_Canceled
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 } Coroutine_Err;
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 typedef struct Coroutine Coroutine;
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 typedef void (*Coroutine_YieldCallback)(void *me);
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 typedef Coroutine_Err (*Coroutine_SystemStart)(void *, Coroutine *);
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 typedef void *(*Coroutine_Start)(void *);
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 Coroutine_API_FUNC(void) Coroutine_SetStackLimit(void *);
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 Coroutine_API_FUNC(Coroutine_Report) Coroutine_GetReport(void);
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 #ifndef NDEBUG
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 Coroutine_API_FUNC(Coroutine_Err) Coroutine_CheckIntegrity(void);
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 #else
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 static inline Coroutine_Err Coroutine_CheckIntegrity(void){return Coroutine_OK;}
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 #endif
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 Coroutine_API_FUNC(Coroutine *) Coroutine_New(size_t min_size, size_t min_headroom, Coroutine_Start start);
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 Coroutine_API_FUNC(Coroutine_Err) Coroutine_RunSystem(size_t min_size, size_t min_headroom, Coroutine_SystemStart start, void *value);
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 Coroutine_API_FUNC(Coroutine_Err) Coroutine_Run(size_t min_size, size_t min_headroom, Coroutine_Start start, void *value, void **result);
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 Coroutine_API_FUNC(void) Coroutine_Delete(Coroutine *cor);
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 Coroutine_API_FUNC(Coroutine_Err) Coroutine_Continue(Coroutine *cor, void *value, bool early);
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 Coroutine_API_FUNC(void *) Coroutine_Yield(void *value, Coroutine_YieldCallback on_yield, void *me);
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 Coroutine_API_FUNC(void *) Coroutine_GetValue(Coroutine *cor);
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 Coroutine_API_FUNC(Coroutine *) Coroutine_GetActive(void);
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 Coroutine_API_FUNC(ptrdiff_t) Coroutine_GetStackHeadroom(void);
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 Coroutine_API_FUNC(void *) Coroutine_GetStackHWM(void);
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 Coroutine_API_FUNC(void) Coroutine_ClearStackForHWM(void);
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 Coroutine_API_FUNC(bool) Coroutine_CanStartCoroutine(size_t size);
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 Coroutine_API_FUNC(size_t) Coroutine_GetUsefulFreeSpace(size_t min_size, size_t overhead);
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 Coroutine_API_FUNC(void *) Coroutine_GetCStackTop(void);
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 Coroutine_API_FUNC(Coroutine_Err) Coroutine_Chain(size_t min_size, size_t min_headroom, Coroutine_Start start, void *value, void **result);
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 Coroutine_API_FUNC(Coroutine_Err) Coroutine_CallWithMaxStack(Coroutine_Start start, void *value, void **result);
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 Coroutine_API_FUNC(bool) Coroutine_IsStarted(void);
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 Coroutine_API_FUNC(bool) Coroutine_IsRunning(Coroutine *cor);
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 Coroutine_API_FUNC(bool) Coroutine_IsComplete(Coroutine *cor);
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 Coroutine_API_FUNC(void) Coroutine_Dump_(void);
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 #include "coroutine_names_undef.h"
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 #endif
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