keep the PID file locked for the lifetime of the process
[qemu.git] / qemu-coroutine.h
1 /*
2 * QEMU coroutine implementation
3 *
4 * Copyright IBM, Corp. 2011
5 *
6 * Authors:
7 * Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
8 * Kevin Wolf <kwolf@redhat.com>
9 *
10 * This work is licensed under the terms of the GNU LGPL, version 2 or later.
11 * See the COPYING.LIB file in the top-level directory.
12 *
13 */
14
15 #ifndef QEMU_COROUTINE_H
16 #define QEMU_COROUTINE_H
17
18 #include <stdbool.h>
19 #include "qemu-queue.h"
20 #include "qemu-timer.h"
21
22 /**
23 * Coroutines are a mechanism for stack switching and can be used for
24 * cooperative userspace threading. These functions provide a simple but
25 * useful flavor of coroutines that is suitable for writing sequential code,
26 * rather than callbacks, for operations that need to give up control while
27 * waiting for events to complete.
28 *
29 * These functions are re-entrant and may be used outside the global mutex.
30 */
31
32 /**
33 * Mark a function that executes in coroutine context
34 *
35 * Functions that execute in coroutine context cannot be called directly from
36 * normal functions. In the future it would be nice to enable compiler or
37 * static checker support for catching such errors. This annotation might make
38 * it possible and in the meantime it serves as documentation.
39 *
40 * For example:
41 *
42 * static void coroutine_fn foo(void) {
43 * ....
44 * }
45 */
46 #define coroutine_fn
47
48 typedef struct Coroutine Coroutine;
49
50 /**
51 * Coroutine entry point
52 *
53 * When the coroutine is entered for the first time, opaque is passed in as an
54 * argument.
55 *
56 * When this function returns, the coroutine is destroyed automatically and
57 * execution continues in the caller who last entered the coroutine.
58 */
59 typedef void coroutine_fn CoroutineEntry(void *opaque);
60
61 /**
62 * Create a new coroutine
63 *
64 * Use qemu_coroutine_enter() to actually transfer control to the coroutine.
65 */
66 Coroutine *qemu_coroutine_create(CoroutineEntry *entry);
67
68 /**
69 * Transfer control to a coroutine
70 *
71 * The opaque argument is passed as the argument to the entry point when
72 * entering the coroutine for the first time. It is subsequently ignored.
73 */
74 void qemu_coroutine_enter(Coroutine *coroutine, void *opaque);
75
76 /**
77 * Transfer control back to a coroutine's caller
78 *
79 * This function does not return until the coroutine is re-entered using
80 * qemu_coroutine_enter().
81 */
82 void coroutine_fn qemu_coroutine_yield(void);
83
84 /**
85 * Get the currently executing coroutine
86 */
87 Coroutine *coroutine_fn qemu_coroutine_self(void);
88
89 /**
90 * Return whether or not currently inside a coroutine
91 *
92 * This can be used to write functions that work both when in coroutine context
93 * and when not in coroutine context. Note that such functions cannot use the
94 * coroutine_fn annotation since they work outside coroutine context.
95 */
96 bool qemu_in_coroutine(void);
97
98
99
100 /**
101 * CoQueues are a mechanism to queue coroutines in order to continue executing
102 * them later. They provide the fundamental primitives on which coroutine locks
103 * are built.
104 */
105 typedef struct CoQueue {
106 QTAILQ_HEAD(, Coroutine) entries;
107 } CoQueue;
108
109 /**
110 * Initialise a CoQueue. This must be called before any other operation is used
111 * on the CoQueue.
112 */
113 void qemu_co_queue_init(CoQueue *queue);
114
115 /**
116 * Adds the current coroutine to the CoQueue and transfers control to the
117 * caller of the coroutine.
118 */
119 void coroutine_fn qemu_co_queue_wait(CoQueue *queue);
120
121 /**
122 * Adds the current coroutine to the head of the CoQueue and transfers control to the
123 * caller of the coroutine.
124 */
125 void coroutine_fn qemu_co_queue_wait_insert_head(CoQueue *queue);
126
127 /**
128 * Restarts the next coroutine in the CoQueue and removes it from the queue.
129 *
130 * Returns true if a coroutine was restarted, false if the queue is empty.
131 */
132 bool qemu_co_queue_next(CoQueue *queue);
133
134 /**
135 * Restarts all coroutines in the CoQueue and leaves the queue empty.
136 */
137 void qemu_co_queue_restart_all(CoQueue *queue);
138
139 /**
140 * Checks if the CoQueue is empty.
141 */
142 bool qemu_co_queue_empty(CoQueue *queue);
143
144
145 /**
146 * Provides a mutex that can be used to synchronise coroutines
147 */
148 typedef struct CoMutex {
149 bool locked;
150 CoQueue queue;
151 } CoMutex;
152
153 /**
154 * Initialises a CoMutex. This must be called before any other operation is used
155 * on the CoMutex.
156 */
157 void qemu_co_mutex_init(CoMutex *mutex);
158
159 /**
160 * Locks the mutex. If the lock cannot be taken immediately, control is
161 * transferred to the caller of the current coroutine.
162 */
163 void coroutine_fn qemu_co_mutex_lock(CoMutex *mutex);
164
165 /**
166 * Unlocks the mutex and schedules the next coroutine that was waiting for this
167 * lock to be run.
168 */
169 void coroutine_fn qemu_co_mutex_unlock(CoMutex *mutex);
170
171 typedef struct CoRwlock {
172 bool writer;
173 int reader;
174 CoQueue queue;
175 } CoRwlock;
176
177 /**
178 * Initialises a CoRwlock. This must be called before any other operation
179 * is used on the CoRwlock
180 */
181 void qemu_co_rwlock_init(CoRwlock *lock);
182
183 /**
184 * Read locks the CoRwlock. If the lock cannot be taken immediately because
185 * of a parallel writer, control is transferred to the caller of the current
186 * coroutine.
187 */
188 void qemu_co_rwlock_rdlock(CoRwlock *lock);
189
190 /**
191 * Write Locks the mutex. If the lock cannot be taken immediately because
192 * of a parallel reader, control is transferred to the caller of the current
193 * coroutine.
194 */
195 void qemu_co_rwlock_wrlock(CoRwlock *lock);
196
197 /**
198 * Unlocks the read/write lock and schedules the next coroutine that was
199 * waiting for this lock to be run.
200 */
201 void qemu_co_rwlock_unlock(CoRwlock *lock);
202
203 /**
204 * Yield the coroutine for a given duration
205 *
206 * Note this function uses timers and hence only works when a main loop is in
207 * use. See main-loop.h and do not use from qemu-tool programs.
208 */
209 void coroutine_fn co_sleep_ns(QEMUClock *clock, int64_t ns);
210
211 #endif /* QEMU_COROUTINE_H */