nod0620 2011-09-29 13:15 å‘表评论
]]>ReentrantLock
ReentrantLock是å¯é‡å…¥çš„互斥é”åQŒé‡ç‚ÒŽ(gu¨©)˜¯é‡å…¥å’Œäº’斥，ReentrantLock ž®†ç”±æœ€˜q‘æˆåŠŸèŽ·å¾—é”的线½E‹æ‰€æŒæœ‰åQŒå½“˜q™ä¸ª¾U¿ç¨‹å†æ¬¡ž®è¯•æ‹¥æœ‰˜q™ä¸ªLock时就是é‡å…¥ã€‚互斥就æ˜?br />在æŸä¸€æ—‰™—´åªæœ‰ä¸€ä¸ªçº¿½E‹èƒ½æŒæœ‰Lockã€?br /> public void lock() {
sync.lock();
}
获得é”方法，Sync是AQS的抽象å¾c»ï¼Œå®žçŽ°å¯é‡å…¥å’Œäº’斥的大部分功能。在Syncçš„å¾cÖM¸æœ‰FairSyncå’ŒNonfairSync两ç§ä»£è¡¨å…¬åã^é”ç–略和éžå…¬òq³é”½{–ç•¥
Sync lockæ–ÒŽ(gu¨©)³•ç•™ç»™åç±»åŽÕd®žçŽŽÍ¼ŒNonfairSync的实玎ͼš(x¨¬)
final void lock() {
if (compareAndSetState(0, 1))
setExclusiveOwnerThread(Thread.currentThread());
else
acquire(1);
}
ä¸ç®¡æ˜¯ä¸æ˜¯æœ‰å…¶ä»–¾U¿ç¨‹åœ¨AQS的阻塞的队列里é¢åQŒå¦‚果当å‰çº¿½E‹èƒ½èŽ·å¾—¾U¿ç¨‹åQŒå°±ç›´æŽ¥èŽ·å¾—¾U¿ç¨‹åQŒä¸è¡Œçš„è¯æ‰§è¡ŒAQSçš„acquire()æ–ÒŽ(gu¨©)³•åQŒåŸºæœ¬å°±æ˜¯è¿›å…¥é˜»å¡žé˜Ÿåˆ—的命了ã€?br />关键ç‚?AQSçš„acquire()ä¸è°ƒç”¨çš„tryAcquire(int arg)是留¾l™å¾cÕd®žçŽ°çš„åQŒæ˜¯åœ¨è¿›å…¥é˜»å¡žé˜Ÿåˆ—å‰å†å°è¯•ä¸€‹Æ¡èŽ·å–é”(lock()æ–ÒŽ(gu¨©)³•åˆ°è¿™ä¸ªç‚¹ä¸Šé¢å¯èƒ½å…¶ä»–¾U¿ç¨‹å·²ç»é‡Šæ”¾é”?
NonfairSync的tryAcquire(int arg)调用的nonfairTryAcquire()实现:
final boolean nonfairTryAcquire(int acquires) {
final Thread current = Thread.currentThread();
int c = getState();
if (c == 0) {//关键�
if (compareAndSetState(0, acquires)) {
setExclusiveOwnerThread(current);
return true;
}
}
else if (current == getExclusiveOwnerThread()) {
int nextc = c + acquires;//关键�
if (nextc < 0) // overflow
throw new Error("Maximum lock count exceeded");
setState(nextc);
return true;
}
return false;
}
关键ç‚?åQšstateä¸?åQŒæ²¡æœ‰çº¿½E‹è¯·æ±‚é”åQŒç›´æŽ¥åˆ†é…给本线½E?br />关键ç‚?. 如果本线½E‹å·²¾l得到é”åQŒstateåŠ?åQŒå³é‡å…¥ã€?br />
FairSync的实�
final void lock() {
acquire(1);//关键�
}
protected final boolean tryAcquire(int acquires) {
final Thread current = Thread.currentThread();
int c = getState();
if (c == 0) {
if (isFirst(current) && //关键�
compareAndSetState(0, acquires)) {
setExclusiveOwnerThread(current);
return true;
}
}
else if (current == getExclusiveOwnerThread()) {
int nextc = c + acquires;
if (nextc < 0)
throw new Error("Maximum lock count exceeded");
setState(nextc);
return true;
}
return false;
}
关键ç‚?åQšå…¬òq³ç–略，没有¾l™å½“å‰çº¿½E‹ä¼˜æƒ?br />关键ç‚?åQšåˆ¤æ–当å‰çº¿½E‹æœ‰æ²¡æœ‰åœ¨é˜»å¡žé˜Ÿåˆ—çš„½W¬ä¸€ä½ï¼Œæ²¡åœ¨½W¬ä¸€ä½ä¸å¾€ä¸‹ç‘ô¾l执行，˜q™æ ·å…ˆç»™é˜Õd¡žé˜Ÿåˆ—的线½E‹æœºä¼?x¨¬)，˜q™æ ·åšé€Ÿåº¦æ¯”较慢，åžåé‡æ¯”较å°
public boolean tryLock() {
return sync.nonfairTryAcquire(1);
}
tryLockž®è¯•èŽ·å¾—é”，ä¸èƒ½èŽ·å¾—è¯å°±ç›´æŽ¥˜q”回åQŒæ²¡æœ‰å…¬òq³ç–略一说ã€?br />
unlock
public void unlock() {
sync.release(1);
}
public final boolean release(int arg) {
if (tryRelease(arg)) {
Node h = head;
if (h != null && h.waitStatus != 0)
unparkSuccessor(h);
return true;
}
return false;
}
tryRelease()留给AQSå类执行åQ?br /> protected final boolean tryRelease(int releases) {
int c = getState() - releases;
if (Thread.currentThread() != getExclusiveOwnerThread())
throw new IllegalMonitorStateException();
boolean free = false;
if (c == 0) {
free = true;
setExclusiveOwnerThread(null);
}
setState(c);
return free;
}
如果state被å‡åŽè¿˜ä¸äØ“(f¨´)0åQŒè¡¨½Cø™¿™ä¸ªé”被一个线½E‹é‡å…¥åŽ˜q˜æ²¡æœ‰å®Œå…¨é‡Šæ”¾ï¼Œrelease()æ–ÒŽ(gu¨©)³•åŽé¢ä¸ä¼š(x¨¬)执行åQŒä¹Ÿž®±æ˜¯ä¸ä¼š(x¨¬)执行unparké˜Õd¡žé˜Ÿåˆ—ä¸çš„¾U¿ç¨‹.
ReentrantReadWriteLock
ReentrantReadWriteLock内部有两个é”åQšäº’æ–¥å¯é‡å…¥çš„WriteLock和共享的ReadLock
内部实现ä¸stateå—段的高16ä½ä»£è¡¨çš„是read countåQŒä½Ž16ä½ä»£è¡¨çš„是write count
AQS的实çŽîC¹Ÿæœ‰NonfairSyncå’ŒFairSync之分åQ?br />主è¦åŒºåˆ«æ˜¯åŒæ—¶æœ‰è¯Õd†™¾U¿ç¨‹æ—¶å€™å¯¹å¾…读写线½E‹ç–ç•¥ä¸åŒã€?br />NonfairSync:
final boolean writerShouldBlock(Thread current) {
return false; // writers can always barge
}
final boolean readerShouldBlock(Thread current) {
/* As a heuristic to avoid indefinite writer starvation,
* block if the thread that momentarily appears to be head
* of queue, if one exists, is a waiting writer. This is
* only a probablistic effect since a new reader will not
* block if there is a waiting writer behind other enabled
* readers that have not yet drained from the queue.
*/
return apparentlyFirstQueuedIsExclusive();
}
write永远都ä¸é˜Õd¡žåQŒreadçš„è¯çœ‹é˜»å¡žé˜Ÿåˆ—header之åŽçš„node是ä¸æ˜¯write的，如果是就é˜Õd¡žåQŒå¯ä»¥é¿å…read一直è¿è¡Œå¯¼è‡´çš„write饥饿ã€?br />FairSyncåQ?br /> final boolean writerShouldBlock(Thread current) {
// only proceed if queue is empty or current thread at head
return !isFirst(current);
}
final boolean readerShouldBlock(Thread current) {
// only proceed if queue is empty or current thread at head
return !isFirst(current);
}
writeå’Œread都有判æ–是ä¸æ˜¯é˜»å¡žé˜Ÿåˆ—headeråŽçš„½W¬ä¸€ä¸ªnodeã€?br />
对于ReadLock
public void lock() {
sync.acquireShared(1);
}
调用AQSçš„acquireShared()åQŒå…¶ä¸ä¼š(x¨¬)执行留给AQSå类实现的tryAcquireShared():
protected final int tryAcquireShared(int unused) {
/*
* Walkthrough:
* 1. If write lock held by another thread, fail
* 2. If count saturated, throw error
* 3. Otherwise, this thread is eligible for
* lock wrt state, so ask if it should block
* because of queue policy. If not, try
* to grant by CASing state and updating count.
* Note that step does not check for reentrant
* acquires, which is postponed to full version
* to avoid having to check hold count in
* the more typical non-reentrant case.
* 4. If step 3 fails either because thread
* apparently not eligible or CAS fails,
* chain to version with full retry loop.
*/
Thread current = Thread.currentThread();
int c = getState();
if (exclusiveCount(c) != 0 &&
getExclusiveOwnerThread() != current)
return -1;
if (sharedCount(c) == MAX_COUNT)
throw new Error("Maximum lock count exceeded");
if (!readerShouldBlock(current) &&
compareAndSetState(c, c + SHARED_UNIT)) {
HoldCounter rh = cachedHoldCounter;
if (rh == null || rh.tid != current.getId())
cachedHoldCounter = rh = readHolds.get();
rh.count++;
return 1;
}
return fullTryAcquireShared(current);
}
½{–ç•¥æ˜¯ä»¥ä¸‹çš„å‡ ç‚¹åQ?br />1.如果当å‰writeæŒæœ‰é”，直接˜q”回-1.
2.没有writeæŒæœ‰é”，判æ–是å¦éœ€è¦é˜»å¡žè¯»è¯äh±‚åQŒä¹‹åŽåŽŸåæ›´æ–°read count
3.上é¢æˆåŠŸåŽå°±˜q”回1åQŒä¸æˆåŠŸçš„è¯åœ¨åó@环ä¸è¯•ç€è¯Õd–åQ?br /> final int fullTryAcquireShared(Thread current) {
/*
* This code is in part redundant with that in
* tryAcquireShared but is simpler overall by not
* complicating tryAcquireShared with interactions between
* retries and lazily reading hold counts.
*/
HoldCounter rh = cachedHoldCounter;
if (rh == null || rh.tid != current.getId())
rh = readHolds.get();
for (;;) {
int c = getState();
int w = exclusiveCount(c);
if ((w != 0 && getExclusiveOwnerThread() != current) ||
((rh.count | w) == 0 && readerShouldBlock(current)))
return -1;
if (sharedCount(c) == MAX_COUNT)
throw new Error("Maximum lock count exceeded");
if (compareAndSetState(c, c + SHARED_UNIT)) {
cachedHoldCounter = rh; // cache for release
rh.count++;
return 1;
}
}
}
unLockæ–ÒŽ(gu¨©)³•ž®±æ˜¯ž®†read count å‡?åQŒç„¶åŽæŸ¥çœ‹é˜»å¡žé˜Ÿåˆ—有没有¾U¿ç¨‹éœ€è¦unpark
WriteLock的实现和ReetrantLock的实现是一致的
Semaphore
Semaphore是信å·é‡çš„概念，主è¦æŽ§åˆ¶åŒä¸€æ—‰™—´å†…对讉K—®èµ„æºçš„线½E‹æ•°çš„控制。底层实现是AQSçš?br />acquireShared()å’ŒreleaseShared().
CountDownLatch
CountDownLatch在完æˆä¸€¾l„æ£åœ¨å…¶ä»–线½E‹ä¸æ‰§è¡Œçš„æ“作之å‰ï¼Œå…许¾U¿ç¨‹½{‰å¾…直到他们完æˆæ“作
await()æ–ÒŽ(gu¨©)³•ä¸€ç›´ç‰åˆ°state=0åQŒåˆå§‹æ—¶CountDownLatchåˆå§‹åŒ–stateä¸ÞZ¼ 入的数å€û|¼Œä¸€ä¸ªçº¿½E?br />执行æ“作完æˆçš„è¯æ‰§è¡ŒcountDown()æ–ÒŽ(gu¨©)³•ž®†stateå‡?åQŒç›´åˆîCØ“(f¨´)0åQŒawait()æ–ÒŽ(gu¨©)³•ä¸å†é˜Õd¡žã€?br />
CyclicBarrier
当一¾l„线½E‹è°ƒç”¨CyclicBarrier.await()æ–ÒŽ(gu¨©)³•åQŒå°±ä¼?x¨¬)阻塞在那里åQŒå½“最åŽä¸€ä¸ªçº¿½E‹è¿›å…¥è°ƒç”¨æ¤æ–ÒŽ(gu¨©)³•æ—Óž¼Œž®±æ‰§è¡?br />一个公å…Þqš„Runnable.原ç†æ˜¯ï¼š(x¨¬)åˆå§‹åŒ–时有count属性，当å‰é¢count-1个线½E‹åˆ°æ¥éƒ½condition.await()åQŒç¬¬countä¸?br />¾U¿ç¨‹æ¥å°±æ‰§è¡Œå…¬å…±RunnableåQŒç„¶åŽæ‰§è¡Œcondition.signAll()æ–ÒŽ(gu¨©)³•æ¥ä‹É得其他线½E‹ä»Žé˜Õd¡žä¸è§£è„±å‡ºæ?
nod0620 2011-09-18 00:12 å‘表评论
]]>nod0620 2011-09-15 22:57 å‘表评论
]]>jdkä¸çº¿½E‹çŠ¶æ€åˆ†ä¸?new,runnable,blocked,waiting,timed_waiting,dead.å…¶ä¸new为刚创徘q˜æ²¡æœ‰å¼€å§‹æ‰§è¡Œçš„状æ€ï¼Œ
而runnable状æ€åˆ†ä¸ºå¯ä»¥æ‰§è¡Œå’Œæ£åœ¨æ‰§è¡ŒåQŒå¯ä»¥æ‰§è¡Œæ˜¯å› äØ“(f¨´)å¯èƒ½è¦ç‰cpuæ—‰™—´ç‰‡ç‰ã€‚blocked状æ€æ˜¯æŒ‡çº¿½E‹åœ¨é˜Õd¡ž½{‰å¾…监视器的é”。waiting是指执行了Object.wait()åQŒThread.join()½{‰æ–¹æ³•è¿›å…¥waiting状æ€ï¼›timed_waiting是指带时间数的waiting状æ€ï¼Œåœ¨æ—¶é—´åˆ°è¾¾ä¹‹å‰éƒ½æ˜¯åœ¨waiting状æ€ï¼Œdead状æ€æ˜¯æŒ‡ç»“æŸä“Q务的¾U¿ç¨‹çŠ¶æ€ï¼Œå†ä¹Ÿä¸èƒ½å›žåˆ°runnable状æ€äº†ã€?br />
在线½E‹ä¸æœ‰waiting setå’Œready set概念ã€?br />当一个对象执行Object.wait()/Object.join()åQŒè¯¥¾U¿ç¨‹˜q›å…¥waiting setåQŒåŒæ—‰™œ€è¦é‡Šæ”„¡›‘视器的é”ã€‚ç›‘è§†å™¨ä¹Ÿæ˜¯ä¸€ä¸ªæ™®é€šå¯¹è±¡ï¼Œåœ¨åŠ ä¸Šä¸€äº›å…³é”®è¯æ³•åŽåQŒå°±èƒ½æˆä¸ºç›‘视器ã€?br />当一个对象执行Object.notify()æ—Óž¼Œæ˜¯åœ¨waiting set选择一个thread˜q›å…¥ready setåQŒå½“˜q™ä¸ªthread能获得这个监视器的é”时候，ž®±å¯ä»¥è¿›å…¥runnable状æ€ï¼Œå¦åˆ™ž®±å¾…在ready setåQŒnotifyAll()是通知waiting set里é¢çš„所有线½E‹ï¼Œç„¶åŽé€‰æ‹©å…¶ä¸çš„一个，ä¸ç¡®å®šæ˜¯å“ªä¸€ä¸ªï¼Œ¾U¿ç¨‹çš„优先çñ”也åªæ˜¯ä¸€ä¸ªæ½Cºå’ŒæŒ‡å¯¼ã€?br />Object.wait(time)/Object.join(time)æ–ÒŽ(gu¨©)³•˜q™äº›éƒ½æ˜¯åœ¨æ—¶é—´é™åˆ¶åˆ°è¾¾ä¹‹å‰thread在waiting setåQŒæ—¶é—´åˆ°æœŸä¹‹åŽè‡ªåŠ¨è¿›å…¥ready setã€?br />Thread.sleep()/Thread.yield()执行时thread都ä¸ä¼?x¨¬)放弃监视器的é”åQŒåªæ˜¯è¿›å…¥ready setåQŒThread.sleep()åªæ˜¯åœ¨æŒ‡å®šçš„æ—‰™—´å†…ä¼‘çœ ï¼Œå¾—ä¸åˆîC“Q何的资æº.Thread.yield()åªæ˜¯æ示thread工作差ä¸å¤šå®Œæˆäº†åQŒå¯ä»¥è®©æ¥ç»™å…¶ä»–ThreadåQŒè¿™ä¸ªè®©æ¥ä¸ä¿è¯å®ŒæˆåQŒè¿™ä¸ªä¹Ÿåªå¯¹åŒç‰¾U§çš„¾U¿ç¨‹æœ‰æ•ˆã€?br />
监视�/strong>
java使用监视器æ¥è¡¨ç¤ºåŒæ¥é”，在Java里é¢åQŒä“Q何一个Object Reference都å¯ä»¥ä½œä¸ºåŒæ¥é”åQŒåªè¦ä‹É用synchronizedåQ?br />
public static final Object signal = new Object();
f1(){
synchronized(signal){
}
}
在jvm内部synchronizedä¼?x¨¬)被表示æˆmonitorenterå’Œmonitorexit;在一个时间段åQŒåªæœ‰ä¸€ä¸ªçº¿½E‹èƒ½æŒæœ‰monitoråQŒä¹Ÿž®±æ˜¯åœ¨monitorenter里é¢åQŒä¹Ÿž®Þp¾¾åˆîCº†åŒæ¥çš„ç›®çš?当想获得一个类å˜é‡é”的时候，å¯ä»¥ä½¿ç”¨˜q™ä¸ª¾cÈš„class¾c…R€?br />f1(){
synchronized(signal){
}
}
内å˜æ¨¡åž‹
在jvm规范ä¸è§„定java内å˜æ¨¡åž‹æ˜¯java thread work memoryå’Œjava main memory两部åˆ?br />æ¯ä¸ªthread一个thread memoryåQŒåˆå§‹äØ“(f¨´)½Iºï¼Œå¿…è¦æ—¶å’Œmain memory通信
规范规定了工作内å˜å’Œä¸Õd†…å˜ä¹‹é—´é€šä¿¡çš?个行为：(x¨¬)use, assign, load, store,read,write, lock, and unlock
use:使用一个线½E‹å·¥ä½œå†…å˜ä¸çš„å˜é‡ï¼Œçœ‹æˆ¾U¿ç¨‹çš„è¡Œä¸?br />assign:讄¡½®ä¸€ä¸ªçº¿½E‹å·¥ä½œå†…å˜ä¸çš„å˜é‡ï¼Œè®„¡½®çš„值æ¥è‡ªçº¿½E‹æ‰§è¡Œå¼•æ“Žï¼Œçœ‹æˆ¾U¿ç¨‹çš„è¡Œä¸?br />readåQšæŠŠä¸Õd†…å˜çš„å€ÆD¯»åˆ°çº¿½E‹å·¥ä½œå†…å˜å½“ä¸ï¼Œçœ‹æˆä¸Õd†…å˜çš„è¡ŒäØ“(f¨´)
loadåQšåœ¨read之åŽæ‰§è¡ŒåQŒçœŸæ£çš„把å€ÆD¯»åˆ°åˆ°å·¥ä½œå†…å˜å½“ä¸åQŒçœ‹æˆçº¿½E‹çš„è¡ŒäØ“(f¨´)
storeåQšä¿å˜å·¥ä½œå†…å˜çš„å€û|¼Œ½{‰ä¸‹åœ¨æ‰§è¡ŒwriteåŽä¼ 输给ä¸Õd†…å˜ï¼Œçœ‹æˆ¾U¿ç¨‹çš„è¡Œä¸?br />
writeåQšåœ¨storeåŽæ‰§è¡Œï¼Œçœ‹æˆä¸Õd†…å˜çš„è¡ŒäØ“(f¨´)
lockå’Œunlock是获å–监视器é”和释放é”çš„è¡ŒäØ“(f¨´)åQŒæ˜¯½W¬ä¸‰æ–¹synchronizedè¡ŒäØ“(f¨´)
˜q™æ ·çš„内å˜æ¨¡åž‹å°±ä¼?x¨¬)有问题åQ?br />¾U¿ç¨‹å·¥ä½œå†…å˜æ˜¯ç‹¬ç«‹çš„åQŒåœ¨å·¥ä½œå†…å˜Açš„å˜é‡è¢«å·¥ä½œå†…å˜B看到需è¦ç»˜q‡A-->ä¸Õd†…å?->B的程度，那么什么时候进行工作内å˜åˆ°ä¸Õd†…å˜çš„通信呢？
˜q™é‡Œéœ€è¦æ¶‰å?qi¨¢ng)åˆ?span style="font-size: 40pt;">¾~“å˜ä¸€è‡´æ€§æ¨¡åž‹ï¼Œå›_·¥ä½œå†…å?¾~“å˜)什么时候刷新和è¯Õd–ä¸Õd†…å˜å¿…™å»éµå¾ªä¸€å®šçš„规则æ‰å¯ä»¥ã€?
java使用释放一致性模åž?在释æ”ùN”的时候写入主内å˜
也就是当synchronized表示的方法或者è¿è¡Œå—执行¾l“æŸæ—¶ç›‘视器é”释攑֎åQŒé‡Œé¢æ¶‰å?qi¨¢ng)的所有å˜é‡?局部å˜é‡é™¤å¤?的值都写入了主内å˜åQŒå½“å˜é‡è¢«å…¶ä»–线½E‹çœ‹åˆ°çš„è¯ï¼Œå…¶å€¼æ˜¯æœ€æ–°çš„ã€?br />那么æ–ÒŽ(gu¨©)³•æˆ–è¿è¡Œå—未进行åŒæ¥ï¼Œå¯èƒ½æœ‰ä¸¤æ–šw¢çš„é—®é¢?
1.æ–ÒŽ(gu¨©)³•çš„执行顺åºæ˜¯æœªå®šçš?br />2.å³ä‹Éæ–ÒŽ(gu¨©)³•çš„执行顺åºæ˜¯ç›¸åŒçš„，ç”׃ºŽå·¥ä½œå†…å˜çš„值未写到ä¸Õd†…å˜ä¸ä¹Ÿæœ‰å¯èƒ½æœ‰é—®é¢?br />
thread在jvm当ä¸æ‰§è¡Œçš„顺åºå’Œä»£ç ä¸çœ‹åˆ°çš„™åºåºå¯èƒ½æ˜¯ä¸ä¸€æ ïL(f¨¥ng)š„åQŒäØ“(f¨´)了性能优化½{‰ä»£ç å¯èƒ½è¿›è¡Œé‡æŽ’åºåQŒæ‰€æœ‰jmm定义äº?br />¾U¿ç¨‹çš„执行顺åºæ¨¡åž‹ï¼š(x¨¬)happens-before模型åQŒè§„则如ä¸?
1.一个线½E‹å½“ä¸ï¼Œå…ˆå‡ºçŽ°çš„指ä×o(h¨´)happens-beforeåŽå‡ºçŽ°çš„指ä×o(h¨´)
2.æž„é€ å™¨çš„é‡Œé¢æŒ‡ä»¤happens-before创å¾å¯¹è±¡çš„指ä»?br />3.对于一个监视器åQŒunlock happens-before 惛_Ž»å¾—é”的指ä»?br />4.对于volatileçš„å˜é‡ï¼Œwrite happens-before read
5.A call to start() on a thread happens-before any actions in the started thread.
6.All actions in a thread happen-before any other thread successfully returns from a
join() on that thread.
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1.All instance fields, static fields and array elements are stored in heap memory.å˜æ”¾åœ¨javaå †å†…
2.
linux¾Uªå½• http://www.aygfsteel.com/nod0620/articles/358026.htmlnod0620 nod0620 Wed, 07 Sep 2011 09:46:00 GMT http://www.aygfsteel.com/nod0620/articles/358026.html http://www.aygfsteel.com/nod0620/comments/358026.html http://www.aygfsteel.com/nod0620/articles/358026.html#Feedback 0 http://www.aygfsteel.com/nod0620/comments/commentRss/358026.html http://www.aygfsteel.com/nod0620/services/trackbacks/358026.html 2.echo,昄¡¤ºæ–‡æœ¬è¡?br />3.whereis command 昄¡¤ºcommand在哪里，whatis command 昄¡¤ºcommand是什ä¹?br />4.free昄¡¤ºå†…å˜ä¿¡æ¯
5.history 昄¡¤ºåŽ†å²æŒ‡ä×o(h¨´)
6.locale 昄¡¤ºå½“剾pÈ»Ÿçš„è¯a€è®„¡½®
7.ps 昄¡¤º˜q›ç¨‹æ¶ˆæ¯ã€?ps aux | grep xxx
8.sysctlå¯ä»¥ç”¨æ¥è®„¡½®æ ¸å¿ƒçš„å‚敎ͼŒé»˜è®¤çš„文件是/etc/sysctl.conf
9.top昄¡¤º˜q›ç¨‹æ¶ˆæ¯åQŒä¸»è¦æ˜¯æŸ¥çœ‹¾pÈ»Ÿçš„ä¸€äº›å…³é”®æ€§èƒ½æŒ‡æ ‡
10.vmstat昄¡¤ºè™šæ‹Ÿå†…嘾lŸè®¡ä¿¡æ¯
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17.查看所有的shell命ä×o(h¨´)åQŒå¯ä»¥è¿›è¡Œä¿®æ”?br />18.export 讄¡½®å’Œæ˜¾½CºçŽ¯å¢ƒå˜é‡?br />19.find 查找文äšg命ä×o(h¨´)
20.wc¾lŸè®¡æ–‡äšg的行敎ͼŒå—æ•°åQŒå—节数åQŒæ–‡ä»¶å
21.grep æ£åˆ™è¡¨è¾¾å¼æœç´?grep xxx æ–‡äšgxxxåQ?i 忽略大å°å†™ï¼›-æ•°å— æ˜„¡¤ºåŒšw…行的上下数å—行；-b 在æ¯è¡Œå‰æ˜„¡¤ºå—符å移é‡?-n 昄¡¤ºè¡Œæ•°
22.tar -cvf 压羃;tar -xvf 解压
linux监控åQ?div>http://agapple.iteye.com/blog/1156719
ps详解åQ?
http://blog.chinaunix.net/space.php?uid=20053649&do=blog&id=161862
top详解åQ?br />
1.All instance fields, static fields and array elements are stored in heap memory.å˜æ”¾åœ¨javaå †å†…
2.
nod0620 2011-09-14 16:53 å‘表评论
]]>5.history 昄¡¤ºåŽ†å²æŒ‡ä×o(h¨´)
6.locale 昄¡¤ºå½“剾pÈ»Ÿçš„è¯a€è®„¡½®
7.ps 昄¡¤º˜q›ç¨‹æ¶ˆæ¯ã€?ps aux | grep xxx
8.sysctlå¯ä»¥ç”¨æ¥è®„¡½®æ ¸å¿ƒçš„å‚敎ͼŒé»˜è®¤çš„文件是/etc/sysctl.conf
9.top昄¡¤º˜q›ç¨‹æ¶ˆæ¯åQŒä¸»è¦æ˜¯æŸ¥çœ‹¾pÈ»Ÿçš„ä¸€äº›å…³é”®æ€§èƒ½æŒ‡æ ‡
10.vmstat昄¡¤ºè™šæ‹Ÿå†…嘾lŸè®¡ä¿¡æ¯
11.pgrep 查找½W¦åˆæ¡äšgçš„è¿›½E?br />12.exit 退出ssh或者终ç«?br />13.pidof 昄¡¤ºå½“å‰æ£åœ¨˜q行的程åºçš„˜q›ç¨‹id
14.kill PIDåQ›pkill process_nameåQ›killall comm æ€æÕd…¨éƒ¨åŒåè¿›½E?br />15.symlinks ½Ž¡ç†å’Œç»´æŠ¤ç¬¦å·é“¾æŽ?br />16.chkconfig 讄¡½®å’Œæ£€æŸ¥ç³»¾lŸçš„æœåŠ¡è®„¡½®
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20.wc¾lŸè®¡æ–‡äšg的行敎ͼŒå—æ•°åQŒå—节数åQŒæ–‡ä»¶å
21.grep æ£åˆ™è¡¨è¾¾å¼æœç´?grep xxx æ–‡äšgxxxåQ?i 忽略大å°å†™ï¼›-æ•°å— æ˜„¡¤ºåŒšw…行的上下数å—行；-b 在æ¯è¡Œå‰æ˜„¡¤ºå—符å移é‡?-n 昄¡¤ºè¡Œæ•°
22.tar -cvf 压羃;tar -xvf 解压
linux监控åQ?div>http://agapple.iteye.com/blog/1156719
ps详解åQ?
http://blog.chinaunix.net/space.php?uid=20053649&do=blog&id=161862
top详解åQ?br />
http://bbs.linuxtone.org/thread-1684-1-1.html
mpstat
mpstat
http://hi.baidu.com/kqzjhack/blog/item/20e1bb6744f9dd36aa184c44.html
http://www.ixpub.net/thread-645961-1-1.html
nod0620 2011-09-07 17:46 å‘表评论
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nod0620 2011-09-07 15:11 å‘表评论
]]>表设è®?/h3>1.求è´æ¶ˆæ¯ä¸»è¦æ˜¯å›¾ç‰‡å’Œæ–‡å—的说明，˜q™ä¸ªå…¶å®žå¯ä»¥çœ‹æˆæ˜¯ä¸ªå¾®åšæ¯ä¸ªç”¨æˆ·å‘表feed的表åQŒä½†æœ‰äº›ä¸åŒåQŒè¿™ä¸ªä¸‹æ–‡å†è¯ß_(d¨¢)¼Œ˜q™é‡Œæˆ‘们å«photo表，下é¢æ‰€è¯´çš„囄¡‰‡ž®±æ˜¯æ±‚è´æ¶ˆæ¯ã€?br />考虑到求è´æ¶ˆæ¯æ¯”较多åQŒæ‰€ä»¥éœ€è¦è¿›è¡Œåˆ†è¡¨ï¼Œå‡è®¾åˆ?个表ã€?strong>ç”׃ºŽä¸šåŠ¡çš„需求是åQšå¯ä»¥æŸ¥çœ‹å•å¼ 图片，å¯ä»¥çœ‹ä¸€ä¸ªç”¨æˆïL(f¨¥ng)š„囄¡‰‡åˆ—表åQŒé—®é¢˜æ¥äº†ï¼Œæˆ‘们按什么进行分表？
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那么一个user_id所有的囄¡‰‡éƒ½åœ¨ä¸€å¼ 表里é¢äº†ï¼Œ˜q™é‡Œå¯¹idž®±æœ‰è¦æ±‚åQŒid对表数é‡å–模的å€ÆD¦å’Œuser_id对表数é‡å–模的å€ég¸€è‡?ã€?br />˜q™æ ·åšçš„¾l“果是，idçš„å€ég¸æ˜¯è¿ž¾lçš„åQŒæœ‰äº›è®¸çš„浪费，如果user_id分布ä¸å‡çš„è¯åQŒå¯¹äºŽæ¯ä¸ªè¡¨çš„æ•°æ®é‡ä¹Ÿä¼š(x¨¬)分布ä¸å‡
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™å¹ç›®ç”¨çš„是pull模å¼åQŒæ³¨æ„到求贙å¹ç›®çš„特ŒDŠæ€§ï¼Œä¸€èˆ¬åªæ˜¯çœ‹æœ€æ–°çš„求è´çš„消æ¯ï¼Œå‡è®¾æŸä¸ªç”¨æˆ·å½“å‰æœ?000æ¡æ–°feedåQŒè¿™ä¸ªç”¨æˆ·ä¹Ÿä¸èƒ½å®Œå…¨çš„看完，所以认为åªè¦å–得最新的消æ¯é‡Œé¢çš„è‹¥òq²æ¡åQŒå…¶ä½™çš„消æ¯çš„è¯å¯ä»¥åœ¨åŽ†å²feed列表里é¢çœ‹åˆ°æˆ–者下一‹Æ¡çœ‹åˆŽÍ¼Œ˜q™é‡Œž®±æœ‰ä¸ªtimeline的概å¿üc(di¨£n)€‚当‹Æ¡å–得最新消æ¯åŽåQŒéœ€è¦æŠŠ˜q™ä¸ªæ—‰™—´ç‚¹ä¿å˜ï¼Œä¸‹æ¬¡æŸ¥è¯¢çš„时候，从这个时间点˜q›è¡ŒæŸ¥è¯¢ã€?br />
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˜q˜æœ‰å¾ˆå¤šä¼˜åŒ–的点没有说出æ¥ï¼Œæ¯”如路由表å–模的时候，是用ä½ä¸Žæ“作çš?18%16==18&15)˜q˜æœ‰å„个能用到cache的地方尽é‡ä‹É用cacheåQŒå¯¹äºŽè¯»å†™çš„è¯ï¼Œå¯ä»¥å¢žåŠ è¯Õd†™é˜Ÿåˆ—.
对于扩展åQŒæ€§èƒ½åQŒåŽ¾l考虑的：(x¨¬)
当å•ä¸ªç”¨æˆ·å…³æ³¨æ•°‘…过一定数目，˜q™ä¸ªç”¨æˆ·ž®±éœ€è¦ç‰¹åˆ«çš„对待åQŒæ¯”如用户关注å•ç‹¬çš„å˜æˆä¸€å¼ 表åQŒå‡ž®‘关注表的压åŠ?br />对用æˆäh´»è·ƒåº¦˜q›è¡Œåˆ†æžåQŒæ´»è·ƒç”¨æˆïL(f¨¥ng)š„feed使用pullå’Œpush模å¼ç›¸ç»“åˆçš„模å¼
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nod0620 2011-08-31 15:50 å‘表评论
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一般是如上囄¡»“æž?br />
Bootstrap ClassLoader/å¯åŠ¨¾cÕdŠ 载器
ä»–çš„parent为null, 主è¦è´Ÿè´£'sun.boot.class.path'¾pÈ»Ÿå±žæ€§æŒ‡å®šçš„ æˆ?-Xbootclasspath 选项指定的jar包装入工ä½?
ä»–çš„parent为null, 主è¦è´Ÿè´£'sun.boot.class.path'¾pÈ»Ÿå±žæ€§æŒ‡å®šçš„ æˆ?-Xbootclasspath 选项指定的jar包装入工ä½?
Bootstrap ClassLoader是jvm控制的，ä¸æ˜¯javaè¯è¨€å±‚颾~–å†™çš„ï¼Œé»˜è®¤åŠ è²jdk_home/jre/lib/下é¢çš„jar包和其他相关的东西，如jdkçš„æ ¸å¿ƒåŒ…rt.jarž®±æ˜¯åœ¨è¿™é‡Œè¢«åŠ è²çš?br />
Extension ClassLoader/扩展¾cÕdŠ 载器
主è¦è´Ÿè´£jdk_home/jre/lib/ext目录ä¸?'java.ext.dirs'¾pÈ»Ÿå±žæ€§æŒ‡å®?çš„jar包或 -Djava.ext.dirs 指定目录下的jar包装入工ä½?ä»–çš„parentä¸?Bootstrap ClassLoader
主è¦è´Ÿè´£jdk_home/jre/lib/ext目录ä¸?'java.ext.dirs'¾pÈ»Ÿå±žæ€§æŒ‡å®?çš„jar包或 -Djava.ext.dirs 指定目录下的jar包装入工ä½?ä»–çš„parentä¸?Bootstrap ClassLoader
System ClassLoader/¾pÈ»Ÿ¾cÕdŠ 载器
主è¦è´Ÿè´£java -classpath/-Djava.class.path所指的目录下的¾cÖM¸Žjar包装入工ä½?一般我们会(x¨¬)é…置环境å˜é‡classpathåQŒè¿™ä¸ªå°±æ˜¯è²å…¥classpath指定的èµ\径下jarå’Œclass,
òq›_¸¸æˆ‘们指定一ä¸?."åøP¼Œž®±æ˜¯æŒ‡å®šä»Žå½“å‰ç›®å½•ä¸‹å¼€å§‹æœç´¢class¾c?parentä¸?Extension ClassLoader.
主è¦è´Ÿè´£java -classpath/-Djava.class.path所指的目录下的¾cÖM¸Žjar包装入工ä½?一般我们会(x¨¬)é…置环境å˜é‡classpathåQŒè¿™ä¸ªå°±æ˜¯è²å…¥classpath指定的èµ\径下jarå’Œclass,
òq›_¸¸æˆ‘们指定一ä¸?."åøP¼Œž®±æ˜¯æŒ‡å®šä»Žå½“å‰ç›®å½•ä¸‹å¼€å§‹æœç´¢class¾c?parentä¸?Extension ClassLoader.
User Custom ClassLoader/ç”¨æˆ·è‡ªå®šä¹‰ç±»åŠ è²å™?java.lang.ClassLoaderçš„å¾c?
在程åºè¿è¡ŒæœŸé—? 通过java.lang.ClassLoaderçš„å¾cÕdŠ è½½classæ–‡äšg.
classloaderè¦åŠ è½½class先从底å‘ä¸Šä¼ é€’ç»™çˆ¶äº²åŠ è²¾c»ï¼Œæœ€™å¶å±‚çš„classloaderå¦‚æžœèƒ½å¤ŸåŠ è²ž®±åŠ 载进æ¥ï¼Œä¸è¡Œçš„è¯åQŒå°±è‡ªä¸Šè€Œä¸‹ä¼ 递，åªåˆ°ä¸€ä¸ªclassloaderèƒ½è¿›è¡Œç±»çš„åŠ è½½ï¼Œ
如果没有一个classloaderèƒ½åŠ è½½çš„è¯ï¼Œž®×ƒ¼š(x¨¬)抛出ClassNotFoundException或者NoClassDefFoundError异常åQŒè¿™ä¸ªå°±æ˜¯åŒäº²å§”‹z¾æ¨¡å¼?br />
classloader˜q™ç§æ¨¡å¼ä¿è¯äº†ä¸åŒçš„classloader之间¾cÖM¸ä¼?x¨¬)相互的影å“åQŒé‚£ä¹ˆä¹Ÿä¿è¯äº†å¥½çš„ç±»ä¸ä¼š(x¨¬)被æ¶æ„çš„¾cÀL‰€ç ´ååQŒè¿™ä¸ªä¹Ÿæ˜¯jvm沙箱模å¼å®‰å…¨çš„一个ä¿è¯?br />
在ä¸åŒclassloaderçš„åŒåçš„¾cÕd®žä¾‹ä¸èƒ½äº’相沟通，¾cÕdž‹è½¬æ¢åQŒinstanceofåQŒå¦‚æžœè¿™æ ·åšåQŒåˆ™ä¼?x¨¬)抛出ClassCastException.所以抛出ClassCastExceptionçš„åŽŸå› ä¸æ¢å’Œ¾l§æ‰¿åQŒå®žçŽ°æœ‰å…³ç³»åQ?br />˜q˜å’Œclassloader有关¾p?
在程åºè¿è¡ŒæœŸé—? 通过java.lang.ClassLoaderçš„å¾cÕdŠ è½½classæ–‡äšg.
classloaderè¦åŠ è½½class先从底å‘ä¸Šä¼ é€’ç»™çˆ¶äº²åŠ è²¾c»ï¼Œæœ€™å¶å±‚çš„classloaderå¦‚æžœèƒ½å¤ŸåŠ è²ž®±åŠ 载进æ¥ï¼Œä¸è¡Œçš„è¯åQŒå°±è‡ªä¸Šè€Œä¸‹ä¼ 递，åªåˆ°ä¸€ä¸ªclassloaderèƒ½è¿›è¡Œç±»çš„åŠ è½½ï¼Œ
如果没有一个classloaderèƒ½åŠ è½½çš„è¯ï¼Œž®×ƒ¼š(x¨¬)抛出ClassNotFoundException或者NoClassDefFoundError异常åQŒè¿™ä¸ªå°±æ˜¯åŒäº²å§”‹z¾æ¨¡å¼?br />
classloader˜q™ç§æ¨¡å¼ä¿è¯äº†ä¸åŒçš„classloader之间¾cÖM¸ä¼?x¨¬)相互的影å“åQŒé‚£ä¹ˆä¹Ÿä¿è¯äº†å¥½çš„ç±»ä¸ä¼š(x¨¬)被æ¶æ„çš„¾cÀL‰€ç ´ååQŒè¿™ä¸ªä¹Ÿæ˜¯jvm沙箱模å¼å®‰å…¨çš„一个ä¿è¯?br />
在ä¸åŒclassloaderçš„åŒåçš„¾cÕd®žä¾‹ä¸èƒ½äº’相沟通，¾cÕdž‹è½¬æ¢åQŒinstanceofåQŒå¦‚æžœè¿™æ ·åšåQŒåˆ™ä¼?x¨¬)抛出ClassCastException.所以抛出ClassCastExceptionçš„åŽŸå› ä¸æ¢å’Œ¾l§æ‰¿åQŒå®žçŽ°æœ‰å…³ç³»åQ?br />˜q˜å’Œclassloader有关¾p?
当è¿è¡Œæ—¶å‘现一个新classè¦loadæ—Óž¼Œé™¤ä»£ç 已指定由哪classloader的实例load外，先由调用者的classloader所在的classloader tree去loadåQŒå¦‚æžœsuper¾c?interface¾cÕd¯¹äºŽè¿™ä¸ªæ ‘(w¨¨i)是新的也一起会(x¨¬)被load。这是caller classloader的概å¿?
åŒäº²å§”æ´¾å¯ä»¥è¢«æ‰“ç ß_(d¨¢)¼Œå…¨æƒè´Ÿè´£ä¹Ÿå¯è¢«æ‰“ç ß_(d¨¢)¼Œæ‰€ä»¥è¿è¡Œæ—¶å†›_®š¾cÀL¥è‡ªå“ªé‡Œï¼Œ˜q˜æ˜¯ç”±classloaderæ ?w¨¨i)å’Œload class的代ç æ˜¯æ€Žæ ·è€Œå†³å®šã€?br />
Thread Context ClassLoaderåQšçº¿½E‹ä¸Šä¸‹æ–‡classloaderåQŒæ˜¯holdä½äº†ä¸€ClassLoader的实例，˜q™ä¸ªholder在线½E‹è¿è¡Œæµ½E‹é‡Œå¯ä»¥åˆ°è¾¾éšå¼ä¼ 递classloader。这个classloader是一个ä¸ä¼?x¨¬)主动load的实例，ž®±æ˜¯è¯´åœ¨˜q™ä¸ª¾U¿ç¨‹˜q行下é‡åˆ°æ–°¾c»è¿™ä¸ªclassloaderä¸ä¼š(x¨¬)ä¸ÕdŠ¨åŽ»loadåQŒåªæœ‰è‡ªå·Þq”¨æ˜‘ּ代ç æˆ–ä½ çœ‹ä¸è§çš„jar里用昑ּ代ç 用这ä¸?div>classloader loadClass()或Class.forName()åQŒæ‰ä¼?x¨¬)ç”Ÿæ•ˆã€‚å› æ¤ï¼Œcaller classloaderå’?thread context classloaderåQŒåœ¨æ‰§è¡ŒåˆîC½ 的代ç æ—¶åQŒå·²å®šã€‚åƈ且执行浽E‹çš„ä¸åŒåQŒåˆ°ä½ 代ç 时的入å£ä¹Ÿä¸åŒåQŒè¢«æ”„¡½®å…¥threadçš„thread context classloaderå’ŒCaller ClassLoaderä¸ä¸€å®šä¸€æ øP¼Œå› æ¤æ˜¯ä¸½E›_®šçš?br />
需è¦ç¨³å®šçš„è¯ï¼Œž®Þp¦ä¿è¯åœ¨è®¾è®¡æ—¶ž®Þp€ƒè™‘到儿Uå…¥å£å’Œç”¨æ³•çš„情况，然åŽå¾—到¼‹®å®šçš„classloaderå˜åœ¨ thread context classloader或者第三方的class loaderä¸ï¼Œtomcatçš„ç±»åŠ è²ä½“ç³»ž®±æ˜¯˜q™æ ·åšçš„.
nod0620 2011-08-24 10:40 å‘表评论
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