lghost1999 commented on issue #3349:
URL: https://github.com/apache/brpc/issues/3349#issuecomment-4766138165
这里通过TaskMeta中的tag去获取对应的taskGroup存在问题，TaskMeta中的tag在bthread创建的时候存在tag设置不正确的情况。当调用
`bthread_start_urgent` 或 `bthread_start_background` 且传入 attr 为 NULL 时，
会创建一个直接在当前worker启动的bthread。运行时已经决定了这个线程属于当前taskGroup，但bthread元数据 TaskMeta
中tag设置的却是 -1，而不是当前taskGroup的tag，具体调用链路如下：
```C++
第一层：bthread.cpp:330-356
int bthread_start_urgent(bthread_t* __restrict tid,
const bthread_attr_t* __restrict attr,
void * (*fn)(void*),
void* __restrict arg) {
bthread::TaskGroup* g =
bthread::BAIDU_GET_VOLATILE_THREAD_LOCAL(tls_task_group);
if (g) {
// if attribute is null use thread local task group
if (bthread::can_run_thread_local(attr)) {
return bthread::TaskGroup::start_foreground(&g, tid, attr, fn,
arg);
}
}
return bthread::start_from_non_worker(tid, attr, fn, arg);
}
int bthread_start_background(bthread_t* __restrict tid,
const bthread_attr_t* __restrict attr,
void * (*fn)(void*),
void* __restrict arg) {
bthread::TaskGroup* g =
bthread::BAIDU_GET_VOLATILE_THREAD_LOCAL(tls_task_group);
if (g) {
// if attribute is null use thread local task group
if (bthread::can_run_thread_local(attr)) {
return g->start_background<false>(tid, attr, fn, arg);
}
}
return bthread::start_from_non_worker(tid, attr, fn, arg);
}
第二层：bthread.cpp:300-303
//判断这个attr的bthread是否可以在本worker中启动，如果不设置attr或者tag匹配，就在本worker中启动
BUTIL_FORCE_INLINE bool can_run_thread_local(const bthread_attr_t*
__restrict attr) {
return attr == nullptr || attr->tag == tls_task_group->tag() ||
attr->tag == BTHREAD_TAG_INVALID;
}
第三层：task_group.cpp:494-564
int TaskGroup::start_foreground(TaskGroup** pg,
bthread_t* __restrict th,
const bthread_attr_t* __restrict attr,
void * (*fn)(void*),
void* __restrict arg) {
if (__builtin_expect(!fn, 0)) {
return EINVAL;
}
const int64_t start_ns = butil::cpuwide_time_ns();
const bthread_attr_t using_attr = (attr ? *attr : BTHREAD_ATTR_NORMAL);
butil::ResourceId<TaskMeta> slot;
TaskMeta* m = butil::get_resource(&slot);
if (BAIDU_UNLIKELY(NULL == m)) {
return ENOMEM;
}
......
}
task_group.cpp:567-618
int TaskGroup::start_background(bthread_t* __restrict th,
const bthread_attr_t* __restrict attr,
void * (*fn)(void*),
void* __restrict arg) {
if (__builtin_expect(!fn, 0)) {
return EINVAL;
}
const int64_t start_ns = butil::cpuwide_time_ns();
const bthread_attr_t using_attr = (attr ? *attr : BTHREAD_ATTR_NORMAL);
butil::ResourceId<TaskMeta> slot;
TaskMeta* m = butil::get_resource(&slot);
if (BAIDU_UNLIKELY(NULL == m)) {
return ENOMEM;
}
......
}
第四层：types.h 140-141
static const bthread_attr_t BTHREAD_ATTR_NORMAL = {BTHREAD_STACKTYPE_NORMAL,
0, NULL,
BTHREAD_TAG_INVALID, {0}};
types.h 38
static const bthread_tag_t BTHREAD_TAG_INVALID = -1;
```
通过上面方式创建的bthread，在获取其TaskMeta中的tag信息，都会返回-1，在调用choose_one_group会直接abort()
```C++
task_group.cpp:350-359
TaskGroup* TaskControl::choose_one_group(bthread_tag_t tag) {
CHECK(tag >= BTHREAD_TAG_DEFAULT && tag < FLAGS_task_group_ntags) << tag;
auto& groups = tag_group(tag);
const auto ngroup = tag_ngroup(tag).load(butil::memory_order_acquire);
if (ngroup != 0) {
return groups[butil::fast_rand_less_than(ngroup)];
}
CHECK(false) << "Impossible: ngroup is 0";
return NULL;
}
```
需要在将taskMeta的tag设置正确
```C++
task_group.cpp
bthread_attr_t using_attr = (attr ? *attr : BTHREAD_ATTR_NORMAL);
//添加代码
if (using_attr.tag == BTHREAD_TAG_INVALID) {
using_attr.tag = tls_task_group ? tls_task_group->tag() :
BTHREAD_TAG_DEFAULT;
}
```
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