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Improvements in handling debug vs release version
jonroach 26 Feb 2026 14:27
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1#ifndef COROUTINE_H
2#define COROUTINE_H
3
4#include <stdbool.h>
5#include <stddef.h>
6#include <stdint.h>
7
8///////////////////////////////////////////////////////////////////////////////
9// Coroutine
10//
11// Coroutines for C, based on setjmp/longjmp.
12// Thread safe - each thread has its own coroutine system
13// Coroutines are cooperatively scheduled
14// Coroutines have their own stack (currently 16K each)
15// A coroutine can be continued, queried, or deleted on a different thread.
16//
17// Usage:
18// Coroutine_StartSystem(); // call once per thread before using coroutines
19// Coroutine *co = Coroutine_New(start_function);
20// void *result;
21// if (Coroutine_Run(co, initial_value, &result)) {
22// // Handle the failure
23// }
24// Coroutine_Delete(co);
25// Coroutine_StopSystem(); // call once per thread when done with coroutines
26//
27// Inside the coroutine function:
28// void *value = Coroutine_Yield(yield_value, on_yield, this);
29// ...
30// return return_value;
31//
32// To create a coroutine:
33// Coroutine *co = Coroutine_New(start_function);
34// To start or continue a coroutine:
35// void *result = Coroutine_Continue(co, value, early);
36// // early=true puts the coroutine at the head of the run queue
37// // early=false puts the coroutine at the tail of the run queue
38// To yield from inside a coroutine:
39// void *value = Coroutine_Yield(yield_value, on_yield, this);
40// // on_yield is called before the next coroutine is run
41// // 'this' is passed to on_yield as its parameter
42// // value is the value passed to Coroutine_Continue
43// To delete a coroutine:
44// Coroutine_Delete(co);
45// To get the value yielded from, or returned by a corotuine:
46// void *value = Coroutine_GetValue(co);
47// To get the currently running coroutine (NULL if none):
48// Coroutine *co = Coroutine_GetActive();
49// To check if a coroutine is currently running:
50// bool running = Coroutine_IsRunning(co);
51//
52// Notes:
53// Coroutine is not expected to be used directly, but as a foundation for
54// higher level constructs such as Generators, Async, etc.
55//
56///////////////////////////////////////////////////////////////////////////////
57
58
59// The stack is used as follows:
60// +------------------+ <- stack top
61// | coroutine header | <- more claimed as needed in Coroutine_New
62// +------------------+ <-
63// | coroutine stack | <-
64// +------------------+ <-
65// | coroutine header |
66// +------------------+
67// | coroutine stack |
68// +------------------+
69// | coroutine header |
70// +------------------+
71// | coroutine stack |
72// +------------------+
73// | coroutine header |
74// +------------------+
75// | coroutine stack |
76// +------------------+
77// | coroutine header |
78// +------------------+
79// | startup space | <- set aside by Coroutine_StartSystem
80// +------------------+
81// | caller | <- This calls Coroutine_StartSystem etc
82// +------------------+
83// | used stack |
84// +------------------+ <- stack bottom
85
86// Each coroutine has this much stack:
87// For Python, we set it to 17 * (enough for a PyEval_EvalDefault), so we get at least 7
88// calls deep before we need a new chunk, ie maximum multi-chunk wastage is under 6% address space.
89//
90// There's a trade-off between smaller chunk sizes, which allow more async tasks to co-exist
91// on a thread, and larger chunk sizes which waste less memory in part-used chunks.
92//
93// ... which means 10000 async tasks need a 2.6 GB stack, which fits comfortably in the address map.
94//
95// Note, when developing the use of Coroutine in Python, the author found the following used
96// excessive amounts of stack space:
97// Tk_Init: on an Intel 64 bit Mac it used 72k.
98// _decimal multplies of big decimal numbers: 256k+640 (2 x 128k buffers in squaretrans_pow2() + workings)
99//
100// 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.
101
102// No coroutine will ask for less stack than this
103#ifndef COROUTINE_MINIMUM_STACK_SIZE
104 #define COROUTINE_MINIMUM_STACK_SIZE (4096 * sizeof(void *))
105#endif
106
107// When Coroutine is started, an amount of stack is set aside to give
108// the caller of Coroutine_StartSystem a bit of room to work before calling
109// Coroutine_Run(), that is this amount:
110#ifndef COROUTINE_STARTUP_STACK_SIZE
111 #define COROUTINE_STARTUP_STACK_SIZE (128 * sizeof(void *))
112#endif
113
114// This is *expensive* to turn on, especially if you have lots of stack pieces (eg when there's lots of Tasks)
115#ifndef COROUTINE_CHECK_INTEGRITY_ON_STACK_CHECK
116 #define COROUTINE_CHECK_INTEGRITY_ON_STACK_CHECK 0
117#endif
118
119#ifndef COROUTINE_RECORD_LOWEST_HEADROOM
120 #define COROUTINE_RECORD_LOWEST_HEADROOM 1
121#endif
122
123// Returned by Coroutine_StopSystem(), this summarises the coroutine session
124typedef struct Coroutine_Report {
125 unsigned coroutines_created;
126 unsigned coroutines_pool_size;
127 size_t lowest_headroom;
128 size_t largest_stack;
129} Coroutine_Report;
130
131typedef enum Coroutine_Err {
132 Coroutine_OK = 0,
133 Coroutine_Err_SystemNotRunning,
134 Coroutine_Err_SystemRunning,
135 Coroutine_Err_NoStack,
136 Coroutine_Err_CoroutineFromWrongThread,
137 Coroutine_Err_ACoroutineIsAlreadyRunning,
138 Coroutine_Err_ExitWithRunningCoroutines,
139 Coroutine_Err_StackOverrun,
140 Coroutine_Err_InternalInsistency,
141 Coroutine_Err_CouldNotInitialiseSystem,
142 Coroutine_Err_WrongState,
143 Coroutine_Err_Canceled
144} Coroutine_Err;
145
146typedef struct Coroutine Coroutine;
147
148typedef void (*Coroutine_YieldCallback)(void *me);
149typedef Coroutine_Err (*Coroutine_SystemStart)(void *);
150typedef void *(*Coroutine_Start)(void *);
151
152extern void Coroutine_SetStackLimit(void *);
153extern Coroutine_Report Coroutine_GetReport(void);
154#ifndef NDEBUG
155 extern Coroutine_Err Coroutine_CheckIntegrity(void);
156#else
157 static inline Coroutine_Err Coroutine_CheckIntegrity(void){return Coroutine_OK;}
158#endif
159extern Coroutine *Coroutine_New(size_t size, Coroutine_Start start);
160extern Coroutine_Err Coroutine_Run_Coroutine(Coroutine *cor, void *value);
161extern Coroutine_Err Coroutine_RunSystem(Coroutine_SystemStart start, void *value);
162extern Coroutine_Err Coroutine_Run(size_t size, Coroutine_Start start, void *value, void **result);
163extern void Coroutine_Delete(Coroutine *cor);
164extern Coroutine_Err Coroutine_Continue(Coroutine *cor, void *value, bool early);
165extern void *Coroutine_Yield(void *value, Coroutine_YieldCallback on_yield, void *me);
166extern void *Coroutine_GetValue(Coroutine *cor);
167extern Coroutine *Coroutine_GetActive(void);
168extern intptr_t Coroutine_GetStackHeadroom(void);
169extern void *Coroutine_GetStackHWM(void);
170extern void Coroutine_ClearStackForHWM(void);
171extern bool Coroutine_CanStartCoroutine(size_t size);
172extern void *Coroutine_GetCStackTop(void);
173extern Coroutine_Err Coroutine_Chain(size_t size, Coroutine_Start start, void *value, void **result);
174extern bool Coroutine_IsStarted(void);
175extern bool Coroutine_IsRunning(Coroutine *cor);
176extern bool Coroutine_IsComplete(Coroutine *cor);
177
178extern void _Coroutine_Dump(void);
179
180#endif
181