端端舝

Concurrent 肮ヽ⻌嬡
絁宒頗扦疋弁本仿
庨ⅲ岈𦲀掛窒
末白玄它尼失嶱逃窒嬡
珂傷撮胍嶱逃窒
? 2017 PIXELA CORPORATION�PIXELA CORPORATION PROPRIETARY AND CONFIDENTIAL.
2019爛6堎21゜

逃桶及醴腔
♀ 穴伙民旦伊永玉皿伕弘仿立件弘卞云仃月�磁卞勾中化眭勻化手日丹
♀ 肮ヽ左皮斥尼弁玄卞勾中化眭勻化手日丹
♀ 穴伙民旦伊永玉偞�/灍蚾及用它甩它毛眭勻化手日丹
2Copyright ? PIXELA CORPORATION. All Rights Reserved.�PIXELA CORPORATION PROPRIETARY AND CONFIDENTIAL.

失斥尼件母
♀ 1: 穴伙民旦伊永玉弁奶朮
♀ 2: �磁午公及埻秪午�習
♀ 3: 肮ヽ左皮斥尼弁玄
♀ 4: 偞�/灍蚾奻及蛁砩
♀ 5: Atomic 劐杅紱釬

1:穴伙民旦伊永玉弁奶朮

仇及戊奈玉及 x 互午曰丹月�反ˋ
5
int x = 0;
void func1() {
for (int i = 0; i < 1000000; i++) x++;
}
int main()
{
std::thread t1([]() { func1(); }), t2([]() { func1(); });
t1.join(); t2.join();
printf("x:%dn", x);
}
Copyright ? PIXELA CORPORATION. All Rights Reserved.�PIXELA CORPORATION PROPRIETARY AND CONFIDENTIAL.

2:�磁午公及埻秪午�習

�磁 (1) : 犯奈正�磁 (data race)
♀ 恚杅旦伊永玉匹肮元劐杅卞�仄化肮媆卞 Read/Write 互逃汜允月
♀ �躇卞反屾卅仁午手珨勾互 Write 午卅月
♀ 逃汜政砓
♀ 睡互逃汜允月井軑砑匹五卅中
♀劐載芴笢及�互 Read (劐杅互伊斥旦正盟毛閉尹月�磁)
♀Write �互坻及旦伊永玉及 Read 卞毀茬今木卅中
♀ 埻秪
♀戊奈玉午 CPU 韜鍔及墊褩
♀CPU 及囀窒�釬 (平乓永扑亙)

�磁 (1) : 犯奈正�磁 (data race)
8
int my_account = 0; // 佌及蕼踢諳釱紹詢
int your_account = 100; // 丐卅凶及蕼踢諳釱紹詢
// 冞踢�I燴
bool racy_transfer(int m) {
if (m <= my_account) { // 帤隅膽�釬及褫夔俶丐曰ㄐ
my_account -= m; // 帤隅膽�釬及褫夔俶丐曰ㄐ
your_account += m; // 帤隅膽�釬及褫夔俶丐曰ㄐ
return true;
}
return false;
}

�磁 (2) : �磁袨颷 (race condition)
♀ 灍俴正奶立件弘卞甡湔仄化扑旦氾丞及堤薯磐彆互劐趙允月
♀ 逃汜政砓
♀ 劐杅互祥劐沭璃卞綃毀仄凶�卞卅月
♀ 正奶立件弘卞方勻化祥撿磁逃汜﹜sleep 毛⻌木月午弁仿永扑亙
♀ 埻秪
♀ 偞�/灍蚾立旦
♀恚杅及伉末奈旦卞�允月紱釬互齬坻今木化中卅中
♀旦伊永玉嶲及捼礿毛俴勻化中卅中

�磁 (2) : �磁袨颷 (race condition)
10
std::atomic<int> my_account = 0; // 佌及蕼踢諳釱紹詢
std::atomic<int> your_account = 100; // 丐卅凶及蕼踢諳釱紹詢
// 冞踢�I燴
bool unsafe_transfer(int m)
{
if (m <= my_account) {
// ∴仇及媆萸匹手(m <= my_account)反淩ˋ
my_account -= m;
your_account += m;
return true;
}
return false;
}

�磁尺及�習 (價掛)
♀ 紱釬毛祥褫煦 (atomic) 午允月
♀ atomic 午反珨窣及紱釬互坻旦伊永玉井日珨极午�尹月仇午
♀�紱釬互俇賸允月引匹坻旦伊永玉井日劐載互�尹卅中
♀紱釬囮㷍媆卞反紱釬ゴ及袨颷卞𥽋月
♀恚杅旦伊永玉匹肮媆卞紱釬匹五卅中
♀ 瞰: 恚杅旦伊永玉井日失弁本旦今木月伉末奈旦毛齬坻允月
♀ ゴ枑沭璃毛㦤凶仄化井日灍俴允月
♀ 坻及旦伊永玉及⻌薯毛渾勾方丹卅�磁

淏仄中戊奈玉
12
int my_account = 0; // 佌及蕼踢諳釱紹詢
int your_account = 100; // 丐卅凶及蕼踢諳釱紹詢
std::mutex txn_guard;
// 冞踢�I燴: 假�卅玄仿件扒弁扑亦件�I燴
bool safe_transfer(int m)
{
std::lock_guard<std::mutex> lk(txn_guard);
if (m <= my_account) {
my_account -= m;
your_account += m;
return true;
}
return false;
}

3:肮ヽ左皮斥尼弁玄

測桶腔卅肮ヽ左皮斥尼弁玄
♀ Mutex
♀ Read-Write Lock
♀ Condition Variable
♀ Event
♀ Semaphore
♀ Volatile (淏復卞反肮ヽ左皮斥尼弁玄匹反卅中)

Mutex
♀ 伕永弁允月仇午匹公木眕蔥及戊奈玉尺及失弁本旦痜毛龰腕允月
♀ 肮媆卞伕永弁匹五月及反珨勾及旦伊永玉及心
♀ 肮元 Mutex 毛伕永弁仄化中月戊奈玉嶲反齬坻今木化中月
♀ Mutex 及釬曰源卞方勻化肮元旦伊永玉互恚杅隙伕永弁毛午木月 (Recursive) 卅手及
午匹五卅中手及互丐月
♀ 由白巧奈穴件旦互猁А今木卅中癹曰 Recursive 卞允月及互假�
♀摽及党淏匹 Recursive 互斛猁卞卅月井手午中丹燴蚕

Mutex 戊奈玉瞰 (C++)
16
int func()
{
static std::recursive_mutex mutex;
std::lock_guard<std::recursive_mutex>
lock(mutex);
static int count = 0;
count++;
return count;
}

Read-Write Lock
♀ Read 反恚杅丐勻化手 race condition 反お五卅中仇午毛瞳蚚仄化由白巧奈穴件旦砃
奻毛俴丹
♀ Read 及伕永弁 API 午 Write API 及伕永弁互煦井木化中月
♀ Read 分仃卅日恚杅龰腕褫
♀ Write 午 Read, 恚杅及 Write 反肮媆卞俴尹卅中
♀ Write 卞掀屯化 Read 互嗣中�磁卞伕永弁渾切媆嶲毛祅𦑩匹五月

Read-Write Lock 戊奈玉瞰 (Win32 API)
18
void init(SRWLOCK* lock) {
InitializeSRWLock(lock);
}
static int count = 0;
int read(SRWLOCK* lock) {
// AcquireSRWLockExclusive 互卅中癹曰籵月
AcquireSRWLockShared(lock);
int ret = count;
ReleaseSRWLockShared(lock);
return ret;
}
int write(int val, SRWLOCK* lock) {
// 坻及 AcquireSRWLockExclusive, AcquireSRWLockShared 互卅中癹曰籵月
AcquireSRWLockExclusive(lock);
count = val;
ReleaseSRWLockExclusive(lock);
}

Condition Variable
♀ 渾辻�互渾辻仄﹜籵眭�互渾辻�毛お�今六月
♀ 渾辻�互渾辻ゴ卞伕永弁左皮斥尼弁玄 (Mutex, Read-Write Lock) 毛挍勻化中月及
互ゴ枑午卅月
♀ 渾辻午祥褫煦卞俴尹月
♀ ※沭璃劐杅§ 午方壬木化中月及反眕狟及方丹卅妏歹木源及凶戶
♀ 渾辻�反�I燴沭璃毛㦤凶仄化中卅中�磁卞渾辻允月
♀ 籵眭�反渾辻�及�I燴沭璃毛㦤凶仄凶袨颷卞仄化籵眭允月

Condition Variable 戊奈玉瞰 (C++)
20
static std::mutex mutex;
static std::condition_variable cond;
bool flag = false;
void wait() {
// flag 互 true 卞卅月引匹渾辻﹝
std::unique_lock<std::mutex> lock(mutex);
cond.wait(lock, []() { return flag; });
flag = false;
}
void wake() {
// 渾辻旦伊永玉毛お仇允
{ std::unique_lock<std::mutex> lock(mutex); flag = true; }
cond.notify_one();
}

Event
♀ 籵眭�互籵眭毛俴丹午渾辻仄化中月旦伊永玉互お�允月
♀ 左皮斥尼弁玄及 Signal (籵勻化方仄) 午 Non-Signal (籵俴砦戶) 毛奪燴允月
♀ Signal 袨颷匹伕永弁午月午 non-Signal 卞卅月/卅日卅中午井﹜場ヽ袨颷本永玄匹五
月午井田伉巨奈扑亦件互中勻天中丐月
♀ 及匹妏丹蕣卞反 OS 及伉白央伊件旦毛切扎氏午掂戈斛猁互丐月
♀ 萎倰腔卅瞰反 I/O 渾切

Event 戊奈玉瞰 (Win32 API)
22
int init(HANDLE *handle) {
// 赻�匹 non-signal 卞卅月場ヽ� non-signal 及奶矛件玄釬傖
*handle = CreateEvent(/*atrtributes*/NULL,/*manual_reset*/FALSE,
/*initial_state*/FALSE, /*name*/NULL );
}
void wait(HANDLE handle) {
// signal 袨颷引匹渾勾
// 赻�匹 non-signal 卞卅月及匹珨僅卞お�允月旦伊永玉反夫午勾
WaitForSingleObject(handle, INFINITE);
}
void wake(HANDLE handle) {
SetEvent(handle);
}

Semaphore
♀ 硌隅隙杅分仃龰腕匹五月
♀ 賤溫反龰腕氪匹卅仁化手方中
♀ 伉末奈旦及僕衄杅及奪燴卞妏尹月反內
♀ Mutex 午沭璃劐杅匹手灍蚾匹五月互＃

Semaphore 戊奈玉瞰 (Win32 API)
24
int func()
{
static HANDLE sem = CreateSemaphore(
/*attributes*/NULL, /*initial count*/5, /*max count*/ 12, /*name*/ NULL
);
WaitForSingleObject(sem, INFINITE); // count--, count > 0 匹伕永弁今木卅中
// �I燴
// count �樓 -> 渾辻旦伊永玉お�
ReleaseSemaphore(sem, /*count*/1, /*[out] prev_count*/NULL);
}

Volatile
♀ 戊件由奶仿卞方月郔羥趙毛滅什
♀ 劐杅失弁本旦媆卞紨棒丟乒伉毛掂心卞俴仁
♀伙奈皿笢及旦伊永玉俋窒匹及劐杅及劐載及𨈘堤卞妏尹月
♀ 憝杅囀匹及韜鍔伉左奈母奈反滅仆卅中
♀戊奈玉及�扴�卞 Read/Write 今木月午ヽ渾允屯五匹反卅
中
♀ Volatile 匹反卅仁羥ピ卅 atomic 辻�卞螸月屯五
♀ Volatile 毛妏丹弗奈旦反眕狟
♀ 俋窒甩奈玉它尼失犯田奶旦毛統桽仄化中月�磁

Volatile 戊奈玉瞰 (C++)
26
// 犯田奶旦�匹劐載今木月白仿弘
extern volatile int flag;
int wait() {
// busy-loop 匹民尼永弁
// 俋窒匹 flag 互 true 卞卅木壬㠙仃月
while (!flag) {};
}

蛁砩萸
♀ 跪肮ヽ左皮斥尼弁玄互妏蚚匹五月/匹五卅中反 OS 支晟惤卞方勻化綃丹
♀ 跪肮ヽ左皮斥尼弁玄互皿伕本旦嶲匹僕衄匹五月/匹五卅中反 OS 甡湔
♀ C++ 及跪左皮斥尼弁玄紱釬互 OS 及升及 API 卞眈絞允月井反 stdlib 及灍蚾甡湔午卅勻
化中月
♀ 由白巧奈穴件旦互斛猁卅日幏中 API 卞ピ曰杸尹月斛猁互丐月
♀ 旦矢奈旦及飲磁奻目永母及 include 反吽謹仄凶
♀ 僕衄左皮斥尼弁玄互 static 劐杅卞卅勻化中月及反旦矢奈旦及飲磁奻卅及匹灍蚾匹反支日
卅中仇午

4:偞�/灍蚾奻及蛁砩

汜及伕永弁左皮斥尼弁玄反㜳歹卅中
♀ 伕永弁左皮斥尼弁玄毛紱釬允月戊奈玉毛眻諉𤩸井卅中
♀ 失件伕永弁允月戊奈玉毛伕永弁Е嶲堤諳及杅分仃𤩸仁斛猁俶
♀ C++ 卅日 std::lock_guard 脹毛妏丹
♀ RAII (Resource Acquisition Is Initialization)
♀ 旦正永弁奻卞及勻凶左皮斥尼弁玄及勹�媆卞伉末奈旦勹�互逃汜
♀ C 及�磁 RAII 反妏尹卅中及匹 goto 由正奈件匹失件伕永弁毛珨井垀卞摩戶月仇午

沭璃劐杅及 spurious wakeup
♀ 沭璃劐杅匹及渾辻�I燴卞化籵眭卅仄匹皮伕永弁賤壺今木月政砓
♀ 埻秪反仿奶皮仿伉囀窒�I燴支甩奈玉它尼失/OS 及飲磁
♀ 逃汜螿僅反仍仁腴中＃反內
♀ �𡛟 : 沭璃劐杅毛妏丹�磁反斛內渾辻皺賸摽卞渾辻沭璃毛民尼永弁
♀ 㦤凶仄化中卅中�磁反婬僅渾辻

犯永玉伕永弁毛滅什凶戶卞每埻秪
♀ 犯永玉伕永弁反 2 �眕奻及伕永弁及龰腕�楓互綃丹午五卞逃汜允月
♀ 杻卞峉卅中弗奈旦
♀ 伕永弁毛龰腕仄凶引引坻乒斥亙奈伙毛網太卞俴五﹜公及乒斥亙奈伙井日赻乒
斥亙奈伙毛網太堤允磊繚互丐月�磁
♀肮元旦伊永玉匹及網太堤仄反�觳卅中互﹜�卅月旦伊永玉匹
及網太堤仄磊繚互丐月午郔�
♀ 乒斥亙奈伙囀卞恚杅伕永弁左皮斥尼弁玄互丐月�磁
♀都卞伕永弁�唗毛珨隅卞允月斛猁互丐月

犯永玉伕永弁毛滅什凶戶卞每袨暿

犯永玉伕永弁毛滅什凶戶卞每 �習
♀ 齬坻Е嶲毛傻仁允月
♀ 乒斥亙奈伙囀及伕永弁左皮斥尼弁玄毛珨勾卞允月
♀ 乒斥亙奈伙眈誑及網太堤仄互逃汜允月由旦毛釬日卅中
♀ 伕永弁毛龰腕仄凶引引坻乒斥亙奈伙毛網壬卅中
♀ 奻弇乒斥亙奈伙及�I燴反奻弇乒斥亙奈伙及旦伊永玉匹�I燴允月
♀ 中勻凶氏奻弇乒斥亙奈伙及正旦弁平亙奈匹忳仃月脹
♀正旦弁平亙奈互�引勻化犯永玉伕永弁卞卅月�磁手 (灍瞰)
♀ 狟弇乒斥亙奈伙及伕永弁毛�I燴井日ピ曰褩允

Sleep 媆嶲反矛旦玄巨白巧奈玄
♀ 跪意 sleep/渾辻憝杅卞傾允媆嶲反公及媆嶲匹及お�毛悵偩仄卅中
♀ 旦伊永玉旦弗斥亙奈伉件弘 (旦伊永玉�珂僅脹) 及飲磁奻お�互渾凶今木月褫夔俶互
丐月
♀ 引凶﹜お�及儕僅反正奶穴奈賃曰煋心及螿僅卞甡湔允月
♀ Windows: 16 millisecond (犯白巧伙玄袨颷)
♀ PC Linux: 4 millisecond (2010 及ロ�)

儕躇卅 Sleep 媆嶲互斛猁卅�磁
♀ 儕躇卞お�匹五月方丹卞允月
♀ 正奶穴奈賃曰煋心螿僅及劐載 (1 msec 儕僅引匹)
♀ 旦伊永玉�珂僅及竘五奻仆
♀ Busy loop 及妸蚚

5:Atomic 劐杅紱釬

伕永弁卞方月左奈田目永玉
♀ 螿楛卞失弁本旦允月劐杅卞伕永弁毛井仃月午由白巧奈穴件旦腴狟
♀ 螿楛卅袨颷民尼永弁
♀ API 網太堤仄 -> 市奈生伙諾嶲尺及痄�
♀ 丟乒伉毛 Atomic 卞紱釬允月劐杅 (淏復卞反丟乒伉毛 Atomic 卞紱釬允月 CPU 韜
鍔) 毛妏尹壬由白巧奈穴件旦互砃奻允月

Atomic 劐杅及ゴ卞每 data race 及埻秪
♀ 戊奈玉午 CPU 韜鍔及墊褩
♀ CPU 囀窒及飲磁
♀ 平乓永扑亙及肮ヽ互價掛俴歹木卅中

Data race : 戊奈玉午 CPU 韜鍔及墊褩 (1)
♀ 狟及�I燴笢匹戊件氾平旦玄旦奶永民午卅勻凶�磁﹜
婬嶱媆反昺及丟乒伉毛掂心煋氏分袨颷匹�I燴婬嶱
今木月
39
int func(int *ptr) {
*ptr++;
}
int func(int *ptr) {
int val = *ptr;
val++;
*ptr = val;
}
云云方公
棒及方丹卞桯嶱今木月

Data race : 戊奈玉午 CPU 韜鍔及墊褩 (2)
♀ 劐杅互伊斥旦正盟卞�引日卅中�磁﹜丟乒伉𤩸五煋
心芴笢匹坻旦伊永玉井日掂心龰日木月褫夔俶互丐月
♀ 穫嗎仄凶袨颷毛掂心煋氏匹仄引丹
40
struct St {
int64_t a;
int64_t b;
};
int set(St *ptr) {
*ptr = { 123, 125 };
}
云云方公
棒及方丹卞桯嶱今木月
struct St {
int64_t a;
int64_t b;
};
int set(St *ptr) {
ptr->a = 123;
ptr->b = 125;
}

Data race : CPU 平乓永扑亙 (1)
41
丟奶件丟乒伉 (DRAM)
L3 平乓永扑亙
L1 平乓永扑亙
L2 平乓永扑亙L2 平乓永扑亙
L1 平乓永扑亙
Core 1 Core 2
♀ 丟乒伉失弁本旦反綈中及匹平乓永
扑亙蕆𦵴毛偞仃月
♀ ⺍講午厒僅及猁�井日恚杅僇卞煦井
木化中月
♀ Core 卞輪中平乓永扑亙反 Core 仍午
卞蚚砩今木化中月

Data race : CPU 平乓永扑亙 (2)
42
丟奶件丟乒伉 (DRAM)
L3 平乓永扑亙
L1 平乓永扑亙
L2 平乓永扑亙L2 平乓永扑亙
L1 平乓永扑亙
Core 1 Core 2
♀ 丐月 Core 匹及丟乒伉𤩸五煋心互坻
及 Core 卞�尹月引匹卞反媆嶲互井
井月
♀ 酘�匹反郔厒 44 clock 珂
♀ �卅月 Core 匹肮元失玉伊旦毛掂心
煋氏匹中凶�磁﹜赻煦及平乓永扑亙
卞丐月�毛掂心煋心𤩸五煋心卞𠸎互
葆井卅中4 clocks
11 clocks
22 clocks
凶仁今氏
伊奶氾件扑
write
媆嶲毛井仃化�歹月

CPU 卞斛猁卅辻夔
♀ 丟乒伉毛眻諉紱釬允月
♀ 丐月 Core 匹及紱釬互坻及 Core 卞允什�尹月
♀ 平乓永扑亙及淕磁俶毛悵勾
♀坻及 Core 毛旦玄奈伙今六月
♀平乓永扑亙嶲及肮ヽ毛午月

Intel X86 CPU 韜鍔
♀ LOCK XADD [mem] r
♀ r = [mem], [mem] = [mem] + r
♀ LOCK CMPXCHG [mem] r eax
♀ if (eax == [mem]) { [mem] = r } else { eax = [mem] }
♀ 仇木日及韜鍔毛妏丹仇午匹 core 嶲及肮ヽ毛午曰勾勾�I燴匹五月

C++ atomic 劐杅
♀ Atomic CPU 韜鍔毛仿永皿仄化仁木月弁仿旦
♀ 劐杅尺及紱釬毛羥ピ卅 atomic CPU 韜鍔卞劐𡥼仄化仁木月
♀ 失奈平氾弁民乓卞方勻化枑鼎今木月申永玄盟脹互綃丹
45
std::atomic<int> val = 128;
void func() {
int chk = 256;
val.compare_exchange_weak(chk, 1024); // lock cmpxchg
val++; // lock xadd
}

C++ atomic 劐杅
♀ 瞳萸 : data race 毛壺�匹五月
♀ セ萸 : 丐月最僅及左奈田奈目永玉互丐月
♀ 都卞丟乒伉奻卞劐杅互饜离今木月丹尹卞 Cache 及淕磁俶毛悵勾�I燴互⻌月
♀肮元平乓永扑亙仿奶件尺及紱釬反旦玄奈伙允月
♀ 妏中源
♀ #include <atomic> 允月
♀ atomic 卞仄凶中劐杅毛 std::atomic<type> 午允月
♀失奈平氾弁民乓卞方勻化 type 卞⻌木木月倰反綃丹

𡛟蚚 :lock-free 失伙打伉朮丞
♀ Compare and Swap (CAS) 毛瞳蚚仄化掂心龰曰�互劐歹日卅中�磁及心紱釬傖髡
今六月
♀ Intel CPU 及韜鍔反 CMPXCHG 分互珨啜腔卅蚚惤反 Compare and Swap
♀ 紱釬笢卞賃曰煋心互⻌勻凶�磁 CAS 互傖髡仄卅中及匹 (岈ゴ卞掂心龰勻凶�午�卅
月�互殿今木月) 傖髡允月引匹伉玄仿奶毛靜曰殿允

Lock 每 free 失伙打伉朮丞瞰
♀ 政婓�互竘仁�方曰手湮五仃木壬竘仁紱釬
♀ Compare and exchange 卞傖髡允木壬 ret 卞反 tmp 互⻌月反內
♀ (ret == tmp) 匹傖髡瓚隅匹五月
48
std::atomic<int> val = 128;
void minus(int sub) {
int tmp = 0; int ret = 0;
do {
ret = tmp = val;
if (sub <= tmp) {
ret = val.compare_exchange_weak(tmp, tmp - sub);
}
} while (ret != tmp);
}

𡛟蚚 : SpinLock
♀ Mutex 午辻夔反肮元分互申斥奈它尼奶玄卞方勻化伕永弁賤溫毛渾勾
♀ 伕永弁�砓�I燴互傻中�磁卞 Mutex 方曰手毀𡛟俶互方中
♀ 扑件弘伙戊失 CPU 匹反砩庤互卅中
♀ 灍蚾反 atomic 劐杅及紱釬匹俴丹

SpinLock 灍蚾
50
class spinlock {
private:
std::atomic_flag state_;
public:
spinlock() : state_(ATOMIC_FLAG_INIT) {}
void lock() {
// busy-wait 匹政婓及袨颷毛伕永弁袨颷卞允月
while (state_.test_and_set(std::memory_order_acquire));
}
void unlock() {
state_.clear(std::memory_order_release); // �毛失件伕永弁袨颷卞允月
}
};
int func() {
static spinlock lock;
std::lock_guard<spinlock> lk(lock);
static int val = 0; return val++;
}

Introduction to conccrent_lock

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Introduction to conccrent_lock

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Introduction to conccrent_lock