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 /** Free list to speed up creation */
  39 static QSLIST_HEAD(, Coroutine) pool = QSLIST_HEAD_INITIALIZER(pool);
  40 static unsigned int pool_size;
  41
  42 typedef struct {
  43     Coroutine base;
  44     void *stack;
  45     jmp_buf env;
  46 } CoroutineUContext;
  47
  48 /**
  49  * Per-thread coroutine bookkeeping
  50  */
  51 typedef struct {
  52     /** Currently executing coroutine */
  53     Coroutine *current;
  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         pthread_setspecific(thread_state_key, s);
  79     }
  80     return s;
  81 }
  82
  83 static void qemu_coroutine_thread_cleanup(void *opaque)
  84 {
  85     CoroutineThreadState *s = opaque;
  86
  87     g_free(s);
  88 }
  89
  90 static void __attribute__((destructor)) coroutine_cleanup(void)
  91 {
  92     Coroutine *co;
  93     Coroutine *tmp;
  94
  95     QSLIST_FOREACH_SAFE(co, &pool, pool_next, tmp) {
  96         g_free(DO_UPCAST(CoroutineUContext, base, co)->stack);
  97         g_free(co);
  98     }
  99 }
 100
 101 static void __attribute__((constructor)) coroutine_init(void)
 102 {
 103     int ret;
 104
 105     ret = pthread_key_create(&thread_state_key, qemu_coroutine_thread_cleanup);
 106     if (ret != 0) {
 107         fprintf(stderr, "unable to create leader key: %s\n", strerror(errno));
 108         abort();
 109     }
 110 }
 111
 112 static void coroutine_trampoline(int i0, int i1)
 113 {
 114     union cc_arg arg;
 115     CoroutineUContext *self;
 116     Coroutine *co;
 117
 118     arg.i[0] = i0;
 119     arg.i[1] = i1;
 120     self = arg.p;
 121     co = &self->base;
 122
 123     /* Initialize longjmp environment and switch back the caller */
 124     if (!setjmp(self->env)) {
 125         longjmp(*(jmp_buf *)co->entry_arg, 1);
 126     }
 127
 128     while (true) {
 129         co->entry(co->entry_arg);
 130         qemu_coroutine_switch(co, co->caller, COROUTINE_TERMINATE);
 131     }
 132 }
 133
 134 static Coroutine *coroutine_new(void)
 135 {
 136     const size_t stack_size = 1 << 20;
 137     CoroutineUContext *co;
 138     ucontext_t old_uc, uc;
 139     jmp_buf old_env;
 140     union cc_arg arg = {0};
 141
 142     /* The ucontext functions preserve signal masks which incurs a system call
 143      * overhead.  setjmp()/longjmp() does not preserve signal masks but only
 144      * works on the current stack.  Since we need a way to create and switch to
 145      * a new stack, use the ucontext functions for that but setjmp()/longjmp()
 146      * for everything else.
 147      */
 148
 149     if (getcontext(&uc) == -1) {
 150         abort();
 151     }
 152
 153     co = g_malloc0(sizeof(*co));
 154     co->stack = g_malloc(stack_size);
 155     co->base.entry_arg = &old_env; /* stash away our jmp_buf */
 156
 157     uc.uc_link = &old_uc;
 158     uc.uc_stack.ss_sp = co->stack;
 159     uc.uc_stack.ss_size = stack_size;
 160     uc.uc_stack.ss_flags = 0;
 161
 162     arg.p = co;
 163
 164     makecontext(&uc, (void (*)(void))coroutine_trampoline,
 165                 2, arg.i[0], arg.i[1]);
 166
 167     /* swapcontext() in, longjmp() back out */
 168     if (!setjmp(old_env)) {
 169         swapcontext(&old_uc, &uc);
 170     }
 171     return &co->base;
 172 }
 173
 174 Coroutine *qemu_coroutine_new(void)
 175 {
 176     Coroutine *co;
 177
 178     co = QSLIST_FIRST(&pool);
 179     if (co) {
 180         QSLIST_REMOVE_HEAD(&pool, pool_next);
 181         pool_size--;
 182     } else {
 183         co = coroutine_new();
 184     }
 185     return co;
 186 }
 187
 188 void qemu_coroutine_delete(Coroutine *co_)
 189 {
 190     CoroutineUContext *co = DO_UPCAST(CoroutineUContext, base, co_);
 191
 192     if (pool_size < POOL_MAX_SIZE) {
 193         QSLIST_INSERT_HEAD(&pool, &co->base, pool_next);
 194         co->base.caller = NULL;
 195         pool_size++;
 196         return;
 197     }
 198
 199     g_free(co->stack);
 200     g_free(co);
 201 }
 202
 203 CoroutineAction qemu_coroutine_switch(Coroutine *from_, Coroutine *to_,
 204                                       CoroutineAction action)
 205 {
 206     CoroutineUContext *from = DO_UPCAST(CoroutineUContext, base, from_);
 207     CoroutineUContext *to = DO_UPCAST(CoroutineUContext, base, to_);
 208     CoroutineThreadState *s = coroutine_get_thread_state();
 209     int ret;
 210
 211     s->current = to_;
 212
 213     ret = setjmp(from->env);
 214     if (ret == 0) {
 215         longjmp(to->env, action);
 216     }
 217     return ret;
 218 }
 219
 220 Coroutine *qemu_coroutine_self(void)
 221 {
 222     CoroutineThreadState *s = coroutine_get_thread_state();
 223
 224     return s->current;
 225 }
 226
 227 bool qemu_in_coroutine(void)
 228 {
 229     CoroutineThreadState *s = pthread_getspecific(thread_state_key);
 230
 231     return s && s->current->caller;
 232 }