xref: /qemu/util/qemu-coroutine.c (revision 6402cbbb) 
1 /*
2  * QEMU coroutines
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 #include "qemu/osdep.h"
16 #include "trace.h"
17 #include "qemu-common.h"
18 #include "qemu/thread.h"
19 #include "qemu/atomic.h"
20 #include "qemu/coroutine.h"
21 #include "qemu/coroutine_int.h"
22 #include "block/aio.h"
23 
24 enum {
25     POOL_BATCH_SIZE = 64,
26 };
27 
28 /** Free list to speed up creation */
29 static QSLIST_HEAD(, Coroutine) release_pool = QSLIST_HEAD_INITIALIZER(pool);
30 static unsigned int release_pool_size;
31 static __thread QSLIST_HEAD(, Coroutine) alloc_pool = QSLIST_HEAD_INITIALIZER(pool);
32 static __thread unsigned int alloc_pool_size;
33 static __thread Notifier coroutine_pool_cleanup_notifier;
34 
35 static void coroutine_pool_cleanup(Notifier *n, void *value)
36 {
37     Coroutine *co;
38     Coroutine *tmp;
39 
40     QSLIST_FOREACH_SAFE(co, &alloc_pool, pool_next, tmp) {
41         QSLIST_REMOVE_HEAD(&alloc_pool, pool_next);
42         qemu_coroutine_delete(co);
43     }
44 }
45 
46 Coroutine *qemu_coroutine_create(CoroutineEntry *entry, void *opaque)
47 {
48     Coroutine *co = NULL;
49 
50     if (CONFIG_COROUTINE_POOL) {
51         co = QSLIST_FIRST(&alloc_pool);
52         if (!co) {
53             if (release_pool_size > POOL_BATCH_SIZE) {
54                 /* Slow path; a good place to register the destructor, too.  */
55                 if (!coroutine_pool_cleanup_notifier.notify) {
56                     coroutine_pool_cleanup_notifier.notify = coroutine_pool_cleanup;
57                     qemu_thread_atexit_add(&coroutine_pool_cleanup_notifier);
58                 }
59 
60                 /* This is not exact; there could be a little skew between
61                  * release_pool_size and the actual size of release_pool.  But
62                  * it is just a heuristic, it does not need to be perfect.
63                  */
64                 alloc_pool_size = atomic_xchg(&release_pool_size, 0);
65                 QSLIST_MOVE_ATOMIC(&alloc_pool, &release_pool);
66                 co = QSLIST_FIRST(&alloc_pool);
67             }
68         }
69         if (co) {
70             QSLIST_REMOVE_HEAD(&alloc_pool, pool_next);
71             alloc_pool_size--;
72         }
73     }
74 
75     if (!co) {
76         co = qemu_coroutine_new();
77     }
78 
79     co->entry = entry;
80     co->entry_arg = opaque;
81     QSIMPLEQ_INIT(&co->co_queue_wakeup);
82     return co;
83 }
84 
85 static void coroutine_delete(Coroutine *co)
86 {
87     co->caller = NULL;
88 
89     if (CONFIG_COROUTINE_POOL) {
90         if (release_pool_size < POOL_BATCH_SIZE * 2) {
91             QSLIST_INSERT_HEAD_ATOMIC(&release_pool, co, pool_next);
92             atomic_inc(&release_pool_size);
93             return;
94         }
95         if (alloc_pool_size < POOL_BATCH_SIZE) {
96             QSLIST_INSERT_HEAD(&alloc_pool, co, pool_next);
97             alloc_pool_size++;
98             return;
99         }
100     }
101 
102     qemu_coroutine_delete(co);
103 }
104 
105 void qemu_aio_coroutine_enter(AioContext *ctx, Coroutine *co)
106 {
107     Coroutine *self = qemu_coroutine_self();
108     CoroutineAction ret;
109 
110     trace_qemu_aio_coroutine_enter(ctx, self, co, co->entry_arg);
111 
112     if (co->caller) {
113         fprintf(stderr, "Co-routine re-entered recursively\n");
114         abort();
115     }
116 
117     co->caller = self;
118     co->ctx = ctx;
119 
120     /* Store co->ctx before anything that stores co.  Matches
121      * barrier in aio_co_wake and qemu_co_mutex_wake.
122      */
123     smp_wmb();
124 
125     ret = qemu_coroutine_switch(self, co, COROUTINE_ENTER);
126 
127     qemu_co_queue_run_restart(co);
128 
129     /* Beware, if ret == COROUTINE_YIELD and qemu_co_queue_run_restart()
130      * has started any other coroutine, "co" might have been reentered
131      * and even freed by now!  So be careful and do not touch it.
132      */
133 
134     switch (ret) {
135     case COROUTINE_YIELD:
136         return;
137     case COROUTINE_TERMINATE:
138         assert(!co->locks_held);
139         trace_qemu_coroutine_terminate(co);
140         coroutine_delete(co);
141         return;
142     default:
143         abort();
144     }
145 }
146 
147 void qemu_coroutine_enter(Coroutine *co)
148 {
149     qemu_aio_coroutine_enter(qemu_get_current_aio_context(), co);
150 }
151 
152 void qemu_coroutine_enter_if_inactive(Coroutine *co)
153 {
154     if (!qemu_coroutine_entered(co)) {
155         qemu_coroutine_enter(co);
156     }
157 }
158 
159 void coroutine_fn qemu_coroutine_yield(void)
160 {
161     Coroutine *self = qemu_coroutine_self();
162     Coroutine *to = self->caller;
163 
164     trace_qemu_coroutine_yield(self, to);
165 
166     if (!to) {
167         fprintf(stderr, "Co-routine is yielding to no one\n");
168         abort();
169     }
170 
171     self->caller = NULL;
172     qemu_coroutine_switch(self, to, COROUTINE_YIELD);
173 }
174 
175 bool qemu_coroutine_entered(Coroutine *co)
176 {
177     return co->caller;
178 }
179