qemu-coroutine.c

   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 "trace.h"
  16 #include "qemu-common.h"
  17 #include "qemu/thread.h"
  18 #include "qemu/atomic.h"
  19 #include "block/coroutine.h"
  20 #include "block/coroutine_int.h"
  21
  22 enum {
  23     POOL_BATCH_SIZE = 64,
  24 };
  25
  26 /** Free list to speed up creation */
  27 static QSLIST_HEAD(, Coroutine) release_pool = QSLIST_HEAD_INITIALIZER(pool);
  28 static unsigned int release_pool_size;
  29 static __thread QSLIST_HEAD(, Coroutine) alloc_pool = QSLIST_HEAD_INITIALIZER(pool);
  30 static __thread Notifier coroutine_pool_cleanup_notifier;
  31
  32 static void coroutine_pool_cleanup(Notifier *n, void *value)
  33 {
  34     Coroutine *co;
  35     Coroutine *tmp;
  36
  37     QSLIST_FOREACH_SAFE(co, &alloc_pool, pool_next, tmp) {
  38         QSLIST_REMOVE_HEAD(&alloc_pool, pool_next);
  39         qemu_coroutine_delete(co);
  40     }
  41 }
  42
  43 Coroutine *qemu_coroutine_create(CoroutineEntry *entry)
  44 {
  45     Coroutine *co = NULL;
  46
  47     if (CONFIG_COROUTINE_POOL) {
  48         co = QSLIST_FIRST(&alloc_pool);
  49         if (!co) {
  50             if (release_pool_size > POOL_BATCH_SIZE) {
  51                 /* Slow path; a good place to register the destructor, too.  */
  52                 if (!coroutine_pool_cleanup_notifier.notify) {
  53                     coroutine_pool_cleanup_notifier.notify = coroutine_pool_cleanup;
  54                     qemu_thread_atexit_add(&coroutine_pool_cleanup_notifier);
  55                 }
  56
  57                 /* This is not exact; there could be a little skew between
  58                  * release_pool_size and the actual size of release_pool.  But
  59                  * it is just a heuristic, it does not need to be perfect.
  60                  */
  61                 release_pool_size = 0;
  62                 QSLIST_MOVE_ATOMIC(&alloc_pool, &release_pool);
  63                 co = QSLIST_FIRST(&alloc_pool);
  64             }
  65         }
  66         if (co) {
  67             QSLIST_REMOVE_HEAD(&alloc_pool, pool_next);
  68         }
  69     }
  70
  71     if (!co) {
  72         co = qemu_coroutine_new();
  73     }
  74
  75     co->entry = entry;
  76     QTAILQ_INIT(&co->co_queue_wakeup);
  77     return co;
  78 }
  79
  80 static void coroutine_delete(Coroutine *co)
  81 {
  82     co->caller = NULL;
  83
  84     if (CONFIG_COROUTINE_POOL) {
  85         if (release_pool_size < POOL_BATCH_SIZE * 2) {
  86             QSLIST_INSERT_HEAD_ATOMIC(&release_pool, co, pool_next);
  87             atomic_inc(&release_pool_size);
  88             return;
  89         }
  90     }
  91
  92     qemu_coroutine_delete(co);
  93 }
  94
  95 static void coroutine_swap(Coroutine *from, Coroutine *to)
  96 {
  97     CoroutineAction ret;
  98
  99     ret = qemu_coroutine_switch(from, to, COROUTINE_YIELD);
 100
 101     qemu_co_queue_run_restart(to);
 102
 103     switch (ret) {
 104     case COROUTINE_YIELD:
 105         return;
 106     case COROUTINE_TERMINATE:
 107         trace_qemu_coroutine_terminate(to);
 108         coroutine_delete(to);
 109         return;
 110     default:
 111         abort();
 112     }
 113 }
 114
 115 void qemu_coroutine_enter(Coroutine *co, void *opaque)
 116 {
 117     Coroutine *self = qemu_coroutine_self();
 118
 119     trace_qemu_coroutine_enter(self, co, opaque);
 120
 121     if (co->caller) {
 122         fprintf(stderr, "Co-routine re-entered recursively\n");
 123         abort();
 124     }
 125
 126     co->caller = self;
 127     co->entry_arg = opaque;
 128     coroutine_swap(self, co);
 129 }
 130
 131 void coroutine_fn qemu_coroutine_yield(void)
 132 {
 133     Coroutine *self = qemu_coroutine_self();
 134     Coroutine *to = self->caller;
 135
 136     trace_qemu_coroutine_yield(self, to);
 137
 138     if (!to) {
 139         fprintf(stderr, "Co-routine is yielding to no one\n");
 140         abort();
 141     }
 142
 143     self->caller = NULL;
 144     coroutine_swap(self, to);
 145 }