[英]boehm-gc : finalizer, and shrink to fit heap
我有2个关于boehm-gc的问题。
当GC收集垃圾对象,GC空闲内存而不调用析构函数,尽管该对象具有析构函数。 我发现GC称为“finailzer”,但我不知道如何注册它......我该怎么办?
当GC收集垃圾时,GC似乎不会调用free()(或其他无内存函数)。 GC似乎没有释放垃圾,而是把它放到GC的内存池中并在下次分配时使用池。 GC在空闲时释放内存池? 如果没有,我可以对GC说“请释放内存池”吗?
PS。 我找不到boehm-gc参考..你能告诉我参考的位置吗?
如果你需要比gc.h
头文件中提供的更多的引用,那么你可能应该在进一步阅读之前阅读垃圾收集器。
你有问题, gc.h
标题有你需要的:
typedef void (*GC_finalization_proc)
GC_PROTO((GC_PTR obj, GC_PTR client_data));
GC_API void GC_register_finalizer
GC_PROTO((GC_PTR obj, GC_finalization_proc fn, GC_PTR cd,
GC_finalization_proc *ofn, GC_PTR *ocd));
GC_API void GC_debug_register_finalizer
GC_PROTO((GC_PTR obj, GC_finalization_proc fn, GC_PTR cd,
GC_finalization_proc *ofn, GC_PTR *ocd));
/* When obj is no longer accessible, invoke */
/* (*fn)(obj, cd). If a and b are inaccessible, and */
/* a points to b (after disappearing links have been */
/* made to disappear), then only a will be */
/* finalized. (If this does not create any new */
/* pointers to b, then b will be finalized after the */
/* next collection.) Any finalizable object that */
/* is reachable from itself by following one or more */
/* pointers will not be finalized (or collected). */
/* Thus cycles involving finalizable objects should */
/* be avoided, or broken by disappearing links. */
/* All but the last finalizer registered for an object */
/* is ignored. */
/* Finalization may be removed by passing 0 as fn. */
/* Finalizers are implicitly unregistered just before */
/* they are invoked. */
/* The old finalizer and client data are stored in */
/* *ofn and *ocd. */
/* Fn is never invoked on an accessible object, */
/* provided hidden pointers are converted to real */
/* pointers only if the allocation lock is held, and */
/* such conversions are not performed by finalization */
/* routines. */
/* If GC_register_finalizer is aborted as a result of */
/* a signal, the object may be left with no */
/* finalization, even if neither the old nor new */
/* finalizer were NULL. */
/* Obj should be the nonNULL starting address of an */
/* object allocated by GC_malloc or friends. */
/* Note that any garbage collectable object referenced */
/* by cd will be considered accessible until the */
/* finalizer is invoked. */
所以你定义一个回调:
typedef <any type at all you want passed to the callback
as data for its own use> MY_ENVIRONMENT;
void my_callback(GC_PTR void_obj, GC_PTR void_environment) {
MY_ENVIRONMENT *env = (MY_ENVIRONMENT)void_environment;
MY_OBJECT *obj = (MY_OBJECT*)void_obj;
// Do finalization here.
}
创建它的环境(如果有的话;否则只传递NULL):
MY_ENVIRONMENT *my_env = new MY_ENVIRONMENT;
// Initialize if necessary.
然后在新分配的对象上注册它:
MY_
MY_ENVIRONMENT old_env;
GC_finalization_proc old_proc;
GC_register_finalizer(new_obj, my_callback, my_env, &old_env, &old_proc);
现在,当收集此特定对象时,将使用您的环境记录调用my_callback
。
至于你的问题2,你错过了这一点。 Boehm GC 取代 malloc / new和free并管理自己的内存竞技场。 它通常决定何时进行收集。 这通常是大多数竞技场已用完的时候。 垃圾收集标识了空闲的块,因此有资格重新分配。 正如API笔记中明确指出的那样,您可以强制收集和无力对象,但这些通常不是必需的。
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