coroutine-ucontext.c

   1 /*
   2  * ucontext coroutine initialization code
   3  *
   4  * Copyright (C) 2006  Anthony Liguori <anthony@codemonkey.ws>
   5  * Copyright (C) 2011  Kevin Wolf <kwolf@redhat.com>
   6  *
   7  * This library is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU Lesser General Public
   9  * License as published by the Free Software Foundation; either
  10  * version 2.0 of the License, or (at your option) any later version.
  11  *
  12  * This library is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15  * Lesser General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public
  18  * License along with this library; if not, see <http://www.gnu.org/licenses/>.
  19  */
  20
  21 /* XXX Is there a nicer way to disable glibc's stack check for longjmp? */
  22 #ifdef _FORTIFY_SOURCE
  23 #undef _FORTIFY_SOURCE
  24 #endif
  25 #include <stdlib.h>
  26 #include <setjmp.h>
  27 #include <stdint.h>
  28 #include <pthread.h>
  29 #include <ucontext.h>
  30 #include "qemu-common.h"
  31 #include "qemu-coroutine-int.h"
  32
  33 enum {
  34     /* Maximum free pool size prevents holding too many freed coroutines */
  35     POOL_MAX_SIZE = 64,
  36 };
  37
  38 typedef struct {
  39     Coroutine base;
  40     void *stack;
  41     jmp_buf env;
  42 } CoroutineUContext;
  43
  44 /**
  45  * Per-thread coroutine bookkeeping
  46  */
  47 typedef struct {
  48     /** Currently executing coroutine */
  49     Coroutine *current;
  50
  51     /** Free list to speed up creation */
  52     QLIST_HEAD(, Coroutine) pool;
  53     unsigned int pool_size;
  54
  55     /** The default coroutine */
  56     CoroutineUContext leader;
  57 } CoroutineThreadState;
  58
  59 static pthread_key_t thread_state_key;
  60
  61 /*
  62  * va_args to makecontext() must be type 'int', so passing
  63  * the pointer we need may require several int args. This
  64  * union is a quick hack to let us do that
  65  */
  66 union cc_arg {
  67     void *p;
  68     int i[2];
  69 };
  70
  71 static CoroutineThreadState *coroutine_get_thread_state(void)
  72 {
  73     CoroutineThreadState *s = pthread_getspecific(thread_state_key);
  74
  75     if (!s) {
  76         s = g_malloc0(sizeof(*s));
  77         s->current = &s->leader.base;
  78         QLIST_INIT(&s->pool);
  79         pthread_setspecific(thread_state_key, s);
  80     }
  81     return s;
  82 }
  83
  84 static void qemu_coroutine_thread_cleanup(void *opaque)
  85 {
  86     CoroutineThreadState *s = opaque;
  87     Coroutine *co;
  88     Coroutine *tmp;
  89
  90     QLIST_FOREACH_SAFE(co, &s->pool, pool_next, tmp) {
  91         g_free(DO_UPCAST(CoroutineUContext, base, co)->stack);
  92         g_free(co);
  93     }
  94     g_free(s);
  95 }
  96
  97 static void __attribute__((constructor)) coroutine_init(void)
  98 {
  99     int ret;
 100
 101     ret = pthread_key_create(&thread_state_key, qemu_coroutine_thread_cleanup);
 102     if (ret != 0) {
 103         fprintf(stderr, "unable to create leader key: %s\n", strerror(errno));
 104         abort();
 105     }
 106 }
 107
 108 static void coroutine_trampoline(int i0, int i1)
 109 {
 110     union cc_arg arg;
 111     CoroutineUContext *self;
 112     Coroutine *co;
 113
 114     arg.i[0] = i0;
 115     arg.i[1] = i1;
 116     self = arg.p;
 117     co = &self->base;
 118
 119     /* Initialize longjmp environment and switch back the caller */
 120     if (!setjmp(self->env)) {
 121         longjmp(*(jmp_buf *)co->entry_arg, 1);
 122     }
 123
 124     while (true) {
 125         co->entry(co->entry_arg);
 126         qemu_coroutine_switch(co, co->caller, COROUTINE_TERMINATE);
 127     }
 128 }
 129
 130 static Coroutine *coroutine_new(void)
 131 {
 132     const size_t stack_size = 1 << 20;
 133     CoroutineUContext *co;
 134     ucontext_t old_uc, uc;
 135     jmp_buf old_env;
 136     union cc_arg arg = {0};
 137
 138     /* The ucontext functions preserve signal masks which incurs a system call
 139      * overhead.  setjmp()/longjmp() does not preserve signal masks but only
 140      * works on the current stack.  Since we need a way to create and switch to
 141      * a new stack, use the ucontext functions for that but setjmp()/longjmp()
 142      * for everything else.
 143      */
 144
 145     if (getcontext(&uc) == -1) {
 146         abort();
 147     }
 148
 149     co = g_malloc0(sizeof(*co));
 150     co->stack = g_malloc(stack_size);
 151     co->base.entry_arg = &old_env; /* stash away our jmp_buf */
 152
 153     uc.uc_link = &old_uc;
 154     uc.uc_stack.ss_sp = co->stack;
 155     uc.uc_stack.ss_size = stack_size;
 156     uc.uc_stack.ss_flags = 0;
 157
 158     arg.p = co;
 159
 160     makecontext(&uc, (void (*)(void))coroutine_trampoline,
 161                 2, arg.i[0], arg.i[1]);
 162
 163     /* swapcontext() in, longjmp() back out */
 164     if (!setjmp(old_env)) {
 165         swapcontext(&old_uc, &uc);
 166     }
 167     return &co->base;
 168 }
 169
 170 Coroutine *qemu_coroutine_new(void)
 171 {
 172     CoroutineThreadState *s = coroutine_get_thread_state();
 173     Coroutine *co;
 174
 175     co = QLIST_FIRST(&s->pool);
 176     if (co) {
 177         QLIST_REMOVE(co, pool_next);
 178         s->pool_size--;
 179     } else {
 180         co = coroutine_new();
 181     }
 182     return co;
 183 }
 184
 185 void qemu_coroutine_delete(Coroutine *co_)
 186 {
 187     CoroutineThreadState *s = coroutine_get_thread_state();
 188     CoroutineUContext *co = DO_UPCAST(CoroutineUContext, base, co_);
 189
 190     if (s->pool_size < POOL_MAX_SIZE) {
 191         QLIST_INSERT_HEAD(&s->pool, &co->base, pool_next);
 192         co->base.caller = NULL;
 193         s->pool_size++;
 194         return;
 195     }
 196
 197     g_free(co->stack);
 198     g_free(co);
 199 }
 200
 201 CoroutineAction qemu_coroutine_switch(Coroutine *from_, Coroutine *to_,
 202                                       CoroutineAction action)
 203 {
 204     CoroutineUContext *from = DO_UPCAST(CoroutineUContext, base, from_);
 205     CoroutineUContext *to = DO_UPCAST(CoroutineUContext, base, to_);
 206     CoroutineThreadState *s = coroutine_get_thread_state();
 207     int ret;
 208
 209     s->current = to_;
 210
 211     ret = setjmp(from->env);
 212     if (ret == 0) {
 213         longjmp(to->env, action);
 214     }
 215     return ret;
 216 }
 217
 218 Coroutine *qemu_coroutine_self(void)
 219 {
 220     CoroutineThreadState *s = coroutine_get_thread_state();
 221
 222     return s->current;
 223 }
 224
 225 bool qemu_in_coroutine(void)
 226 {
 227     CoroutineThreadState *s = pthread_getspecific(thread_state_key);
 228
 229     return s && s->current->caller;
 230 }