《Java 并发编程·JUC 源码与容器》15.3 JUC 误用清单与 Code Review

public boolean reserve(String isbn) {
    Integer stock = inventory.get(isbn);
    if (stock == null || stock <= 0) return false;
    inventory.put(isbn, stock - 1);
    return true;
}

[P0] 第 3–5 行：get 与 put 是两次独立调用，中间可以被其他线程插入。
     复现：64 线程 × 4000 次，本机 12 次运行里 11 次超卖，最多 3537 本；
           库存字段始终落在 0，所以「库存 >= 0」的断言不会失败。
     改法：换成 compute；售出计数必须在 lambda 内完成，不能放外面。

public boolean reserve(String isbn) {
    boolean[] ok = {false};
    inventory.compute(isbn, (k, v) -> {
        if (v == null || v <= 0) return v;
        ok[0] = true;
        return v - 1;
    });
    return ok[0];
}

// 改前：锁持有时间 = 状态变更 + 下游 RPC
synchronized (this) {
    int left = stock.decrementAndGet();
    notifier.send(isbn, left);          // 800 ms
}

// 改后：锁只保护状态变更，RPC 在锁外
int left;
synchronized (this) { left = stock.decrementAndGet(); }
notifier.send(isbn, left);

#!/usr/bin/env bash
# scan_juc.sh — 粗筛 JUC 误用。启发式，结论要人看。
set -uo pipefail
root="${1:-src}"; out="$(mktemp)"; trap 'rm -f "$out"' EXIT

put() { printf '%s\t%s\t%s:%s\t%s\n' "$1" "$2" "$3" "$4" "$5" >>"$out"; }

rule() {  # rule <级别> <规则名> <ERE>
  grep -rnE --include='*.java' -- "$3" "$root" 2>/dev/null |
  while IFS= read -r hit; do
    local f="${hit%%:*}" r="${hit#*:}"
    put "$1" "$2" "$f" "${r%%:*}" \
        "$(printf '%s' "${r#*:}" | sed 's/^[[:space:]]*//' | cut -c1-58)"
  done
}

after() {  # after <级别> <规则名> <锚点> <窗口内 ERE>：看锚点后 6 行
  grep -rnE --include='*.java' -- "$3" "$root" 2>/dev/null |
  while IFS= read -r hit; do
    local f="${hit%%:*}" r="${hit#*:}"; local ln="${r%%:*}"
    local w; w="$(sed -n "${ln},$((ln + 6))p" "$f")"
    local c; c="$(printf '%s\n' "$w" | grep -nE -- "$4" | head -1)"
    [ -z "$c" ] || put "$1" "$2" "$f" "$ln" \
        "$(printf '%s' "$c" | cut -d: -f2- | sed 's/^[[:space:]]*//' | cut -c1-58)"
  done
}

volatile_compound() {  # volatile int x 之后出现 x++ / x += n
  grep -rnE --include='*.java' 'volatile[[:space:]]+(int|long)[[:space:]]+([A-Za-z_][A-Za-z0-9_]*);' "$root" |
  while IFS= read -r hit; do
    local f="${hit%%:*}" r="${hit#*:}" n
    n="$(printf '%s' "${r#*:}" | sed -E 's/.*[[:space:]]([A-Za-z_][A-Za-z0-9_]*);.*/\1/')"
    grep -nE -- "(^|[^A-Za-z0-9_])${n}(\+\+|--|[[:space:]]*[-+*/]?=)" "$f" |
    while IFS=: read -r l c; do
      put P0 VOLATILE-CMPD "$f" "$l" "$(printf '%s' "$c" | sed 's/^[[:space:]]*//')"
    done
  done
}

rule P0 RAW-THREAD      'new[[:space:]]+Thread[[:space:]]*\('
rule P0 THREAD-STOP     '\.stop\(\)'
rule P0 STATIC-FMT      'static[[:space:]].*SimpleDateFormat'
rule P0 STATIC-MUTABLE  'static[[:space:]]+(final[[:space:]]+)?(HashMap|Map|ArrayList|List|HashSet|Set)<'
rule P1 CHECK-THEN-ACT  '\.containsKey\('
rule P1 SYNC-MAP        'Collections\.synchronizedMap'
rule P1 UNBOUNDED-QUEUE 'new[[:space:]]+LinkedBlockingQueue<>\('
rule P1 STATIC-TL       'static[[:space:]]+.*ThreadLocal'
rule P1 INTERRUPT-SWALLOW 'catch[[:space:]]*\(InterruptedException'
rule P2 FIXED-POOL      'Executors\.newFixedThreadPool'
rule P2 CACHED-POOL     'Executors\.newCachedThreadPool'
rule P2 WALL-CLOCK      'System\.currentTimeMillis\(\)'
rule P2 SLEEP           'Thread\.sleep\('
volatile_compound
after P1 SYNC-IO 'synchronized[[:space:]]*\(' '\.(send|post|execute|invoke|publish)\('

sort -t$'\t' -k1,1 -k2,2 -k3,3 "$out" |
awk -F'\t' '{printf "%-3s %-18s %-42s %s\n", $1, $2, $3, $4}'
printf '\n按级别: '; cut -f1 "$out" | sort | uniq -c | tr '\n' ' '; echo
printf '总计 %s 处\n' "$(wc -l <"$out" | tr -d ' ')"

P0  RAW-THREAD         src/com/plume/conc/core/LoanService.java:17 new Thread(() -> notifySms(isbn)).start();
P0  STATIC-FMT         src/com/plume/conc/core/LoanService.java:8 private static final SimpleDateFormat FMT = new SimpleDate
P0  STATIC-MUTABLE     src/com/plume/conc/core/Cache.java:7       private static final Map<String, String> LEGACY =
P0  STATIC-MUTABLE     src/com/plume/conc/core/LoanService.java:9 private static final Map<String, Integer> STOCK = new Hash
P0  THREAD-STOP        src/com/plume/conc/core/Legacy.java:6      t.stop();
P0  VOLATILE-CMPD      src/com/plume/conc/core/Counter.java:7     count++;
P1  CHECK-THEN-ACT     src/com/plume/conc/core/Cache.java:13      if (!LEGACY.containsKey(k)) {
P1  CHECK-THEN-ACT     src/com/plume/conc/core/LoanService.java:21 if (STOCK.containsKey(isbn)) {
P1  INTERRUPT-SWALLOW  src/com/plume/conc/core/Cache.java:25      } catch (InterruptedException e) {
P1  INTERRUPT-SWALLOW  src/com/plume/conc/core/Timing.java:11     } catch (InterruptedException e) {
P1  STATIC-TL          src/com/plume/conc/core/Cache.java:9       private static final ThreadLocal<String> CTX = new ThreadL
P1  SYNC-IO            src/com/plume/conc/core/LoanService.java:14 mailClient.send(memberId, "reserved " + isbn);
P1  SYNC-MAP           src/com/plume/conc/core/Cache.java:8       Collections.synchronizedMap(new HashMap<>());
P1  UNBOUNDED-QUEUE    src/com/plume/conc/core/PoolFactory.java:16 new LinkedBlockingQueue<>());
P2  CACHED-POOL        src/com/plume/conc/core/PoolFactory.java:11 return Executors.newCachedThreadPool();
P2  FIXED-POOL         src/com/plume/conc/core/PoolFactory.java:7 return Executors.newFixedThreadPool(8);
P2  SLEEP              src/com/plume/conc/core/Cache.java:24      Thread.sleep(10);
P2  SLEEP              src/com/plume/conc/core/Timing.java:10     Thread.sleep(5);
P2  WALL-CLOCK         src/com/plume/conc/core/Timing.java:14     long now = System.currentTimeMillis();
P2  WALL-CLOCK         src/com/plume/conc/core/Timing.java:5      private long last = System.currentTimeMillis();

按级别:    6 P0    8 P1    6 P2 
总计 20 处

#!/usr/bin/env bash
# ci_gate.sh — 把扫描结果变成合并闸门
set -euo pipefail

out="$(tools/scan_juc.sh conc-core/src/main/java)"
printf '%s\n' "$out"

p0="$(printf '%s\n' "$out" | grep -c '^P0' || true)"
p1="$(printf '%s\n' "$out" | grep -c '^P1' || true)"
printf 'summary: P0=%s P1=%s\n' "$p0" "$p1"

if [ "$p0" -gt 0 ]; then
  echo "block: $p0 处 P0，先清干净再合并"
  exit 1
fi
if [ "$p1" -gt 3 ]; then
  echo "warn: $p1 处 P1，需要 reviewer 逐条确认"
fi

summary: P0=6 P1=8
block: 6 处 P0，先清干净再合并