File:  [Qemu by Fabrice Bellard] / qemu / coroutine-ucontext.c
Revision 1.1.1.1 (vendor branch): download - view: text, annotated - select for diffs
Tue Apr 24 19:16:36 2018 UTC (3 years, 1 month ago) by root
Branches: qemu, MAIN
CVS tags: qemu1001, HEAD
qemu 1.0.1

    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 QLIST_HEAD(, Coroutine) pool = QLIST_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:     QLIST_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 = QLIST_FIRST(&pool);
  179:     if (co) {
  180:         QLIST_REMOVE(co, 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:         QLIST_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: }

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