To see the difference, imagine the following story about burgers:

### Concurrent Burgers { #concurrent-burgers }

You go with your crush to get fast food, you stand in line while the cashier takes the orders from the people in front of you. 😍

<img src="/img/async/concurrent-burgers/concurrent-burgers-01.png" class="illustration">

import java.util.HashMap;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

import org.apache.lucene.search.TotalHits.Relation;
import org.codelibs.fess.entity.FacetInfo;

	CurrentSendCalls int64 // CurrentSendCalls is the number of concurrent async Send calls to all targets
	CurrentQueue     int   // Populated if target has a store.
	TotalEvents      int64
	FailedEvents     int64 // Number of failed events per target
}

// TargetList - holds list of targets indexed by target ID.
type TargetList struct {
	// The number of concurrent async Send calls to all targets
	currentSendCalls  atomic.Int64

// - Write operations via updateStats.
// - Read operations via toServerHTTPStats(false).
func TestRaulStatsRaceCondition(t *testing.T) {
	httpStats := newHTTPStats()
	// Simulate the concurrent scenario from the original race condition:
	// Multiple HTTP request handlers updating stats concurrently,
	// while background processes are reading the stats for persistence.

    /**
     * Reserved flag for future use
     */
    int DCERPC_RESERVED_1 = 0x08;
    /**
     * Supports concurrent multiplexing flag
     */
    int DCERPC_CONC_MPX = 0x10; /* supports concurrent multiplexing */
    /**
     * Did not execute flag - indicates request was not executed
     */
    int DCERPC_DID_NOT_EXECUTE = 0x20;
    /**

import java.util.Arrays;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.DisplayName;

import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.lang.ref.WeakReference;
import java.util.ConcurrentModificationException;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import org.jspecify.annotations.Nullable;

/**
 * A builder of {@link ConcurrentMap} instances that can have keys or values automatically wrapped

<img src="/img/async/concurrent-burgers/concurrent-burgers-05.png" class="illustration">

기다리며 대화하는 동안, 때때로 여러분은 카운터에 표시되는 번호를 확인해 여러분 차례인지 봅니다.

그러다 어느 순간 마침내 여러분 차례가 됩니다. 여러분은 카운터에 가서 햄버거를 받고, 테이블로 돌아옵니다.

<img src="/img/async/concurrent-burgers/concurrent-burgers-06.png" class="illustration">

여러분과 짝사랑 상대는 햄버거를 먹으며 좋은 시간을 보냅니다. ✨

<img src="/img/async/concurrent-burgers/concurrent-burgers-07.png" class="illustration">

  public void decrement() {
    add(-1L);
  }

  /**
   * Returns the current sum. The returned value is NOT an atomic snapshot; invocation in
   * the absence of concurrent updates returns an accurate result, but concurrent updates that occur
   * while the sum is being calculated might not be incorporated.
   *
   * @return the sum
   */
  @Override
  public long sum() {
    long sum = base;

 * views are modifiable.
 *
 * <p>This class is not threadsafe when any concurrent operations update the multimap. Concurrent
 * read operations will work correctly if the last write <i>happens-before</i> any reads. To allow
 * concurrent update operations, wrap your multimap with a call to {@link
 * Multimaps#synchronizedSetMultimap}.
 *