#include <chrono>
#include <cstdint>
class SnowflakeGenerator {
public:
SnowflakeGenerator(uint16_t worker_id) : worker_id_(worker_id) {}
uint64_t NextID() {
std::chrono::time_point<std::chrono::system_clock> now =
std::chrono::system_clock::now();
uint64_t timestamp =
std::chrono::duration_cast<std::chrono::milliseconds>(now.time_since_epoch()).count();
uint64_t sequence = 0;
if (timestamp == last_timestamp_) {
sequence = (sequence_ + 1) & kSequenceMask;
if (sequence == 0) {
// If the generated ID in the current millisecond exceeds the maximum value, wait for the next millisecond
timestamp = NextTimestamp(last_timestamp_);
}
} else {
sequence = 0;
}
last_timestamp_ = timestamp;
sequence_ = sequence;
uint64_t id = ((timestamp - kEpoch) << kTimestampShift) |
(worker_id_ << kWorkerIdShift) | sequence;
return id;
}
private:
uint64_t NextTimestamp(uint64_t last_timestamp) {
std::chrono::time_point<std::chrono::system_clock> now =
std::chrono::system_clock::now();
uint64_t timestamp =
std::chrono::duration_cast<std::chrono::milliseconds>(now.time_since_epoch()).count();
while (timestamp <= last_timestamp) {
now = std::chrono::system_clock::now();
timestamp =
std::chrono::duration_cast<std::chrono::milliseconds>(now.time_since_epoch()).count();
}
return timestamp;
}
static const uint64_t kEpoch = 1625097600000; // 2021-07-01 00:00:00.000
static const uint64_t kSequenceBits = 12;
static const uint64_t kWorkerIdBits = 10;
static const uint64_t kMaxWorkerId = (1 << kWorkerIdBits) - 1;
static const uint64_t kSequenceMask = (1 << kSequenceBits) - 1;
static const uint64_t kTimestampShift = kSequenceBits + kWorkerIdBits;
static const uint64_t kWorkerIdShift = kSequenceBits;
uint16_t worker_id_;
uint64_t last_timestamp_ = 0;
uint64_t sequence_ = 0;
};
int main() {
SnowflakeGenerator generator(1);
for (int i = 0; i < 10; ++i) {
uint64_t id = generator.NextID();
printf("%llu\n", id);
}
return 0;
}
