flatmap operator= 导致死锁

[zhaojinzhou]

Describe the bug

To Reproduce

暂时无法复现。
运行时 偶发死锁，并且一直死循环在这个函数中。
很旧版本的brpc 无此问题。

Expected behavior

Versions
OS: ubuntu 20.04
Compiler: g++ 8.4
brpc: 1.13.0
protobuf: 3.6.9

Additional context/screenshots

[zhaojinzhou]

！！！ 实锤，以下代码 会死锁。 碰到赋值语句，立刻死锁。 希望尽早修复

#include
#include
#include
#include
#include

inline uint64_t find_power2(uint64_t b) {
b -= 1;
b |= (b >> 1);
b |= (b >> 2);
b |= (b >> 4);
b |= (b >> 8);
b |= (b >> 16);
b |= (b >> 32);
return b + 1;
}

inline size_t flatmap_round(size_t nbucket) {
#ifdef FLAT_MAP_ROUND_BUCKET_BY_USE_NEXT_PRIME
return find_next_prime(nbucket);
#else
// the lowerbound fixes the corner case of nbucket=0 which results in coredump during seeking the map.
return nbucket <= 8 ? 8 : find_power2(nbucket);
#endif
}

static bool is_too_crowded(size_t size, size_t nbucket, uint32_t load_factor) {
return size * 100 >= nbucket * load_factor;
}

int main() {
size_t new_nbucket =16;
size_t size = 14;
do {
new_nbucket = flatmap_round(16);
static int i=0;
i++;
if (i % 1000 == 0) {
std::cout << "new_buckets_and_thumbnail: ";
}
} while (is_too_crowded(size, new_nbucket, 80));

}