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本文次要钻研一下 jedis 的 borrow 行为
borrowObject
org/apache/commons/pool2/impl/GenericObjectPool.java
public T borrowObject(final Duration borrowMaxWaitDuration) throws Exception {assertOpen();
final AbandonedConfig ac = this.abandonedConfig;
if (ac != null && ac.getRemoveAbandonedOnBorrow() && (getNumIdle() < 2) &&
(getNumActive() > getMaxTotal() - 3)) {removeAbandoned(ac);
}
PooledObject<T> p = null;
// Get local copy of current config so it is consistent for entire
// method execution
final boolean blockWhenExhausted = getBlockWhenExhausted();
boolean create;
final long waitTimeMillis = System.currentTimeMillis();
while (p == null) {
create = false;
p = idleObjects.pollFirst();
if (p == null) {p = create();
if (p != null) {create = true;}
}
if (blockWhenExhausted) {if (p == null) {if (borrowMaxWaitDuration.isNegative()) {p = idleObjects.takeFirst();
} else {p = idleObjects.pollFirst(borrowMaxWaitDuration);
}
}
if (p == null) {
throw new NoSuchElementException(appendStats("Timeout waiting for idle object, borrowMaxWaitDuration=" + borrowMaxWaitDuration));
}
} else if (p == null) {throw new NoSuchElementException(appendStats("Pool exhausted"));
}
if (!p.allocate()) {p = null;}
if (p != null) {
try {factory.activateObject(p);
} catch (final Exception e) {
try {destroy(p, DestroyMode.NORMAL);
} catch (final Exception e1) {// Ignore - activation failure is more important}
p = null;
if (create) {
final NoSuchElementException nsee = new NoSuchElementException(appendStats("Unable to activate object"));
nsee.initCause(e);
throw nsee;
}
}
if (p != null && getTestOnBorrow()) {
boolean validate = false;
Throwable validationThrowable = null;
try {validate = factory.validateObject(p);
} catch (final Throwable t) {PoolUtils.checkRethrow(t);
validationThrowable = t;
}
if (!validate) {
try {destroy(p, DestroyMode.NORMAL);
destroyedByBorrowValidationCount.incrementAndGet();} catch (final Exception e) {// Ignore - validation failure is more important}
p = null;
if (create) {
final NoSuchElementException nsee = new NoSuchElementException(appendStats("Unable to validate object"));
nsee.initCause(validationThrowable);
throw nsee;
}
}
}
}
}
updateStatsBorrow(p, Duration.ofMillis(System.currentTimeMillis() - waitTimeMillis));
return p.getObject();}- borrowObject 办法会开启一个 while 循环，条件是 p 为 null，也就是要获取到 p 或者是外部本人跳出循环；idleObjects.pollFirst()从连接池获取，如果为 null 则执行 create，之后是 blockWhenExhausted 的判断逻辑，如果 create 进去的为 null，则阻塞期待 takeFirst 或者 pollFirst(borrowMaxWaitDuration)，如果还是 null 则抛出 NoSuchElementException；如果 blockWhenExhausted 为 false 然而 create 为 null 则抛出
Pool exhausted - 如果不是 null，则再次确认下 object 的状态，如果变更状态 (
PooledObjectState.IDLE-->PooledObjectState.ALLOCATED) 不胜利则返回 null；接着执行 factory.activateObject(p)办法，如果出现异常则 destory 掉(jedis 这里只是在 db 不一样的时候会从新 select，默认能够了解为空操作)，紧接着是 testOnBorrow 的逻辑 - 这里就是如果 idleObjects.pollFirst()为 null 会触发 create，如果还是 null 则间接抛出 NoSuchElementException 异样，跳出循环；只有在不为 null 且 allocate 失败的时候会重置为 null 持续循环；另外如果是 create 进去的然而 activate 不胜利也会抛出 NoSuchElementException 异样，跳出循环
create
/**
* Attempts to create a new wrapped pooled object.
* <p>
* If there are {@link #getMaxTotal()} objects already in circulation
* or in process of being created, this method returns null.
* </p>
*
* @return The new wrapped pooled object
*
* @throws Exception if the object factory's {@code makeObject} fails
*/
private PooledObject<T> create() throws Exception {int localMaxTotal = getMaxTotal();
// This simplifies the code later in this method
if (localMaxTotal < 0) {localMaxTotal = Integer.MAX_VALUE;}
final long localStartTimeMillis = System.currentTimeMillis();
final long localMaxWaitTimeMillis = Math.max(getMaxWaitDuration().toMillis(), 0);
// Flag that indicates if create should:
// - TRUE: call the factory to create an object
// - FALSE: return null
// - null: loop and re-test the condition that determines whether to
// call the factory
Boolean create = null;
while (create == null) {synchronized (makeObjectCountLock) {final long newCreateCount = createCount.incrementAndGet();
if (newCreateCount > localMaxTotal) {
// The pool is currently at capacity or in the process of
// making enough new objects to take it to capacity.
createCount.decrementAndGet();
if (makeObjectCount == 0) {// There are no makeObject() calls in progress so the
// pool is at capacity. Do not attempt to create a new
// object. Return and wait for an object to be returned
create = Boolean.FALSE;
} else {// There are makeObject() calls in progress that might
// bring the pool to capacity. Those calls might also
// fail so wait until they complete and then re-test if
// the pool is at capacity or not.
makeObjectCountLock.wait(localMaxWaitTimeMillis);
}
} else {
// The pool is not at capacity. Create a new object.
makeObjectCount++;
create = Boolean.TRUE;
}
}
// Do not block more if maxWaitTimeMillis is set.
if (create == null &&
(localMaxWaitTimeMillis > 0 &&
System.currentTimeMillis() - localStartTimeMillis >= localMaxWaitTimeMillis)) {create = Boolean.FALSE;}
}
if (!create.booleanValue()) {return null;}
final PooledObject<T> p;
try {p = factory.makeObject();
if (getTestOnCreate() && !factory.validateObject(p)) {createCount.decrementAndGet();
return null;
}
} catch (final Throwable e) {createCount.decrementAndGet();
throw e;
} finally {synchronized (makeObjectCountLock) {
makeObjectCount--;
makeObjectCountLock.notifyAll();}
}
final AbandonedConfig ac = this.abandonedConfig;
if (ac != null && ac.getLogAbandoned()) {p.setLogAbandoned(true);
p.setRequireFullStackTrace(ac.getRequireFullStackTrace());
}
createdCount.incrementAndGet();
allObjects.put(new IdentityWrapper<>(p.getObject()), p);
return p;
}create 办法不会判断 createCount，如果超出则返回 null，如果期待超出 maxWait 也会返回 null；如果判断要创立则通过 factory.makeObject()，另外针对 testOnCreate 且 validateObject 不通过的也返回 null，如果是有异样则间接抛出
makeObject
redis/clients/jedis/JedisFactory.java
@Override
public PooledObject<Jedis> makeObject() throws Exception {
Jedis jedis = null;
try {jedis = new Jedis(jedisSocketFactory, clientConfig);
jedis.connect();
return new DefaultPooledObject<>(jedis);
} catch (JedisException je) {if (jedis != null) {
try {jedis.quit();
} catch (RuntimeException e) {logger.warn("Error while QUIT", e);
}
try {jedis.close();
} catch (RuntimeException e) {logger.warn("Error while close", e);
}
}
throw je;
}
}JedisFactory 的 makeObject 会创立 Jedis 而后执行 connect，如果有 JedisException 则抛出，这个也会间接跳出 borrowObject 的循环，间接给到调用方
activateObject
redis/clients/jedis/JedisFactory.java
public void activateObject(PooledObject<Jedis> pooledJedis) throws Exception {final BinaryJedis jedis = pooledJedis.getObject();
if (jedis.getDB() != clientConfig.getDatabase()) {jedis.select(clientConfig.getDatabase());
}
}JedisFactory 的 activateObject 就是判断 db 跟配置的是不是一样，不一样则从新 select
testOnBorrow
if (p != null && getTestOnBorrow()) {
boolean validate = false;
Throwable validationThrowable = null;
try {validate = factory.validateObject(p);
} catch (final Throwable t) {PoolUtils.checkRethrow(t);
validationThrowable = t;
}
if (!validate) {
try {destroy(p, DestroyMode.NORMAL);
destroyedByBorrowValidationCount.incrementAndGet();} catch (final Exception e) {// Ignore - validation failure is more important}
p = null;
if (create) {
final NoSuchElementException nsee = new NoSuchElementException(appendStats("Unable to validate object"));
nsee.initCause(validationThrowable);
throw nsee;
}
}
}
public static void checkRethrow(final Throwable t) {if (t instanceof ThreadDeath) {throw (ThreadDeath) t;
}
if (t instanceof VirtualMachineError) {throw (VirtualMachineError) t;
}
// All other instances of Throwable will be silently swallowed
}testOnBorrow 的逻辑就是执行 validateObject 办法，如果是 ThreadDeath 或者 VirtualMachineError 才会从新抛出，否则吞掉，之后判断 validate 后果，如果不胜利则执行 destory 办法，从新设置为 null，然而如果这个是 create 进去的则抛出 NoSuchElementException
小结
jedis 的 borrow 行为是在 while 循环外头去获取的，个别是在 allocate 变更状态不胜利 (PooledObjectState.IDLE-->PooledObjectState.ALLOCATED) 的时候会从新设置 null，持续循环
- idleObjects.pollFirst()为 null 会触发 create，如果还是 null 则抛出 NoSuchElementException(
Pool exhausted)跳出循环；如果 blockWhenExhausted 为 true，block 之后获取到的还是 null，也会抛出 NoSuchElementException(Timeout waiting for idle object)跳出循环；如果触发 create 操作，且 create 抛出 JedisException，这个也会间接跳出 borrowObject 的循环，间接给到调用方 - borrow 进去不会 null 的执行 activateObject，jedis 这里只是在 db 不一样的时候会从新 select，默认能够了解为空操作
-
最初是 testOnBorrow 的逻辑，如果有异样，则针对 create 进去的则抛出 NoSuchElementException 跳出循环，否则重置为 null 持续循环
总结一下就是如果是 create 有异样 (
JedisException) 则间接抛出，如果 borrow 不到 (即便通过 create) 也会抛出 NoSuchElementException(具体可能是 Pool exhausted 或者 Timeout waiting for idle object)，如果有 testOnBorrow 不通过且是 create 进去的，也会抛出 NoSuchElementException(Unable to validate object)