b = clients; ; b = next) {
if (b == null) {
if (pred == null)
clients = subscription;
else
pred.next = subscription;
subscription.onSubscribe();
break;
}
next = b.next;
if (b.isDisabled()) { // remove
if (pred == null)
clients = next;
else
pred.next = next;
}
else if (subscriber.equals(b.subscriber)) {
present = true;
break;
}
pred = b;
}
}
if (present)
subscriber.onError(new IllegalStateException("Already subscribed"));
else if (complete)
subscription.onComplete();
}
/**
* Publishes the given item to each current subscriber by
* asynchronously invoking its onNext method, blocking
* uninterruptibly while resources for any subscriber are
* unavailable.
*
* If the Executor for this publisher throws a
* RejectedExecutionException (or any other RuntimeException or
* Error) when attempting to asynchronously notify subscribers,
* then this exception is rethrown.
*
* @param item the (non-null) item to publish
* @throws IllegalStateException if closed
* @throws NullPointerException if item is null
* @throws RejectedExecutionException if thrown by Executor
*/
public void submit(T item) {
if (item == null) throw new NullPointerException();
synchronized (this) {
if (closed)
throw new IllegalStateException("Closed");
BufferedSubscription pred = null, next;
for (BufferedSubscription b = clients; b != null; b = next) {
int stat;
next = b.next;
if ((stat = b.submit(item)) < 0) {
if (pred == null)
clients = next;
else
pred.next = next;
}
else
pred = b;
}
}
}
/**
* Publishes the given item, if possible, to each current
* subscriber by asynchronously invoking its onNext method. The
* item may be dropped by one or more subscribers if resource
* limits are exceeded, in which case the given handler (if
* non-null) is invoked, and if it returns true, retried once.
* Other calls to methods in this class by other threads are
* blocked while the handler is invoked. Unless recovery is
* assured, options are usually limited to logging the error
* and/or issuing an onError signal to the subscriber.
*
* If the Executor for this publisher throws a
* RejectedExecutionException (or any other RuntimeException or
* Error) when attempting to asynchronously notify subscribers, or
* the drop handler throws an exception when processing a dropped
* item, then this exception is rethrown.
*
* @param item the (non-null) item to publish
* @param onDrop if non-null, the handler invoked upon a drop to a
* subscriber, with arguments of the subscriber and item; if it
* returns true, an offer is re-attempted (once)
* @return the number of drops (failed attempts to issue the item
* to a subscriber)
* @throws IllegalStateException if closed
* @throws NullPointerException if item is null
* @throws RejectedExecutionException if thrown by Executor
*/
public int offer(T item,
BiPredicate, ? super T> onDrop) {
if (item == null) throw new NullPointerException();
int drops = 0;
synchronized (this) {
if (closed)
throw new IllegalStateException("Closed");
BufferedSubscription pred = null, next;
for (BufferedSubscription b = clients; b != null; b = next) {
int stat;
next = b.next;
if ((stat = b.offer(item)) == 0 &&
onDrop != null &&
onDrop.test(b.subscriber, item))
stat = b.offer(item);
if (stat < 0) {
if (pred == null)
clients = next;
else
pred.next = next;
}
else {
pred = b;
if (stat == 0)
++drops;
}
}
return drops;
}
}
/**
* Publishes the given item, if possible, to each current
* subscriber by asynchronously invoking its onNext method,
* blocking while resources for any subscription are unavailable,
* up to the specified timeout or the caller thread is
* interrupted, at which point the given handler (if non-null) is
* invoked, and if it returns true, retried once. (The drop
* handler may distinguish timeouts from interrupts by checking
* whether the current thread is interrupted.) Other calls to
* methods in this class by other threads are blocked while the
* handler is invoked. Unless recovery is assured, options are
* usually limited to logging the error and/or issuing an onError
* signal to the subscriber.
*
* If the Executor for this publisher throws a
* RejectedExecutionException (or any other RuntimeException or
* Error) when attempting to asynchronously notify subscribers, or
* the drop handler throws an exception when processing a dropped
* item, then this exception is rethrown.
*
* @param item the (non-null) item to publish
* @param timeout how long to wait for resources for any subscriber
* before giving up, in units of {@code unit}
* @param unit a {@code TimeUnit} determining how to interpret the
* {@code timeout} parameter
* @param onDrop if non-null, the handler invoked upon a drop to a
* subscriber, with arguments of the subscriber and item; if it
* returns true, an offer is re-attempted (once)
* @return the number of drops (failed attempts to issue the item
* to a subscriber)
* @throws IllegalStateException if closed
* @throws NullPointerException if item is null
* @throws RejectedExecutionException if thrown by Executor
*/
public int offer(T item, long timeout, TimeUnit unit,
BiPredicate, ? super T> onDrop) {
if (item == null) throw new NullPointerException();
long nanos = unit.toNanos(timeout);
int drops = 0;
synchronized (this) {
if (closed)
throw new IllegalStateException("Closed");
BufferedSubscription pred = null, next;
for (BufferedSubscription b = clients; b != null; b = next) {
int stat;
next = b.next;
if ((stat = b.offerNanos(item, nanos)) == 0 &&
onDrop != null && onDrop.test(b.subscriber, item))
stat = b.offer(item);
if (stat < 0) {
if (pred == null)
clients = next;
else
pred.next = next;
}
else {
pred = b;
if (stat == 0)
++drops;
}
}
}
return drops;
}
/**
* Unless already closed, issues onComplete signals to current
* subscribers, and disallows subsequent attempts to publish.
*/
public void close() {
if (!closed) {
BufferedSubscription b, next;
synchronized (this) {
b = clients;
clients = null;
closed = true;
}
while (b != null) {
next = b.next;
b.onComplete();
b = next;
}
}
}
/**
* Unless already closed, issues onError signals to current
* subscribers with the given error, and disallows subsequent
* attempts to publish.
*
* @param error the onError argument sent to subscribers
* @throws NullPointerException if error is null
*/
public void closeExceptionally(Throwable error) {
if (error == null)
throw new NullPointerException();
if (!closed) {
BufferedSubscription b, next;
synchronized (this) {
b = clients;
clients = null;
closed = true;
}
while (b != null) {
next = b.next;
b.onError(error);
b = next;
}
}
}
/**
* Returns true if this publisher is not accepting submissions.
*
* @return true if closed
*/
public boolean isClosed() {
return closed;
}
/**
* Returns true if this publisher has any subscribers.
*
* @return true if this publisher has any subscribers
*/
public boolean hasSubscribers() {
boolean nonEmpty = false;
if (!closed) {
synchronized (this) {
BufferedSubscription pred = null, next;
for (BufferedSubscription b = clients; b != null; b = next) {
next = b.next;
if (b.isDisabled()) {
if (pred == null)
clients = next;
else
pred.next = next;
}
else {
nonEmpty = true;
break;
}
}
}
}
return nonEmpty;
}
/**
* Returns the Executor used for asynchronous delivery.
*
* @return the Executor used for asynchronous delivery
*/
public Executor getExecutor() {
return executor;
}
/**
* Returns the initial per-subscriber buffer capacity.
*
* @return the initial per-subscriber buffer capacity
*/
public int getInitialBufferCapacity() {
return minBufferCapacity;
}
/**
* Returns the maximum per-subscriber buffer capacity.
*
* @return the maximum per-subscriber buffer capacity
*/
public int getMaxBufferCapacity() {
return maxBufferCapacity;
}
/**
* Returns a list of current subscribers.
*
* @return list of current subscribers
*/
public List> getSubscribers() {
ArrayList> subs = new ArrayList<>();
synchronized (this) {
BufferedSubscription pred = null, next;
for (BufferedSubscription b = clients; b != null; b = next) {
next = b.next;
if (b.isDisabled()) {
if (pred == null)
clients = next;
else
pred.next = next;
}
else
subs.add(b.subscriber);
}
}
return subs;
}
/**
* Returns true if the given Subscriber is currently subscribed.
*
* @param subscriber the subscriber
* @return true if currently subscribed
*/
public boolean isSubscribed(Flow.Subscriber subscriber) {
if (!closed) {
synchronized (this) {
BufferedSubscription pred = null, next;
for (BufferedSubscription b = clients; b != null; b = next) {
next = b.next;
if (b.isDisabled()) {
if (pred == null)
clients = next;
else
pred.next = next;
}
else if (subscriber == b.subscriber)
return true;
}
}
}
return false;
}
/**
* Returns an estimate of the number of buffered items (those
* produced but not consumed), summed across all current
* subscribers.
*
* @return the estimate
*/
public long estimateBuffered() {
long sum = 0L;
synchronized (this) {
BufferedSubscription pred = null, next;
for (BufferedSubscription b = clients; b != null; b = next) {
next = b.next;
if (b.isDisabled()) {
if (pred == null)
clients = next;
else
pred.next = next;
}
else
sum += b.estimateBuffered();
}
}
return sum;
}
/**
* A bounded (ring) buffer with integrated control to start a
* consumer task whenever items are available. The buffer
* algorithm is similar to one used inside ForkJoinPool,
* specialized for the case of at most one concurrent producer and
* consumer, and power of two buffer sizes. This allows methods to
* operate without locks even while supporting resizing, blocking,
* task-triggering, and garbage-free buffers (nulling out elements
* when consumed), although supporting these does impose a bit of
* overhead compared to plain fixed-size ring buffers.
*
* The publisher guarantees a single producer via its lock. We
* ensure in this class that there is at most one consumer. The
* request and cancel methods must be fully thread-safe but are
* coded to exploit the most common case in which they are only
* called by consumers (usually within onNext).
*
* This class also serves as its own consumer task, consuming as
* many items/signals as possible before terminating, at which
* point it is re-executed when needed. (The dual Runnable and
* ForkJoinTask declaration saves overhead when executed by
* ForkJoinPools, without impacting other kinds of Executors.)
* Execution control is managed using the ACTIVE ctl bit. We
* ensure that a task is active when consumable items (and
* usually, SUBSCRIBE, ERROR or COMPLETE signals) are present and
* there is demand (unfulfilled requests). This is complicated on
* the creation side by the possibility of exceptions when trying
* to execute tasks. These eventually force DISABLED state, but
* sometimes not directly. On the task side, termination (clearing
* ACTIVE) may race with producers or request() calls, so in some
* cases requires a re-check, re-activating if possible.
*
* The ctl field also manages run state. When DISABLED, no further
* updates are possible. Disabling may be preceded by setting
* ERROR or COMPLETE (or both -- ERROR has precedence), in which
* case the associated Subscriber methods are invoked, possibly
* synchronously if there is no active consumer task (including
* cases where execute() failed). The cancel() method is supported
* by treating as ERROR but suppressing onError signal.
*
* Support for blocking also exploits the fact that there is only
* one possible waiter. ManagedBlocker-compatible control fields
* are placed in this class itself rather than in wait-nodes.
* Blocking control relies on the "waiter" field. Producers set
* the field before trying to block, but must then recheck (via
* offer) before parking. Signalling then just unparks and clears
* waiter field. If the producer and consumer are both in the same
* ForkJoinPool, the producer attempts to help run consumer tasks
* that it forked before blocking.
*
* This class uses @Contended and heuristic field declaration
* ordering to reduce memory contention on BufferedSubscription
* itself, but it does not currently attempt to avoid memory
* contention (especially including card-marks) among buffer
* elements, that can significantly slow down some usages.
* Addressing this may require allocating substantially more space
* than users expect.
*/
@SuppressWarnings("serial")
@sun.misc.Contended
static final class BufferedSubscription extends ForkJoinTask
implements Runnable, Flow.Subscription, ForkJoinPool.ManagedBlocker {
// Order-sensitive field declarations
long timeout; // > 0 if timed wait
volatile long demand; // # unfilled requests
final int minCapacity; // initial buffer size
int maxCapacity; // reduced on OOME
int putStat; // offer result for ManagedBlocker
volatile int ctl; // atomic run state flags
volatile int head; // next position to take
volatile int tail; // next position to put
volatile Object[] array; // buffer: null if disabled
Flow.Subscriber subscriber; // null if disabled
Executor executor; // null if disabled
volatile Throwable pendingError; // holds until onError issued
volatile Thread waiter; // blocked producer thread
T putItem; // for offer within ManagedBlocker
BufferedSubscription next; // used only by publisher
// ctl values
static final int ACTIVE = 0x01; // consumer task active
static final int DISABLED = 0x02; // final state
static final int ERROR = 0x04; // signal onError then disable
static final int SUBSCRIBE = 0x08; // signal onSubscribe
static final int COMPLETE = 0x10; // signal onComplete when done
static final long INTERRUPTED = -1L; // timeout vs interrupt sentinel
BufferedSubscription(Flow.Subscriber subscriber,
Executor executor, int minBufferCapacity,
int maxBufferCapacity) {
this.subscriber = subscriber;
this.executor = executor;
this.minCapacity = minBufferCapacity;
this.maxCapacity = maxBufferCapacity;
}
final boolean isDisabled() {
return ctl == DISABLED;
}
final int estimateBuffered() {
int n;
return (ctl != DISABLED && (n = tail - head) > 0) ? n : 0;
}
/**
* Tries to add item and start consumer task if necessary.
* @return -1 if disabled, 0 if dropped, else 1
*/
final int offer(T item) {
Object[] a = array;
int t = tail, h = head, n, i, stat;
if (a != null && (n = a.length) > t - h && (i = t & (n - 1)) >= 0) {
a[i] = item;
U.putOrderedInt(this, TAIL, t + 1);
}
else if ((stat = growAndAdd(a, item)) <= 0)
return stat;
for (int c;;) { // possibly start task
Executor e;
if (((c = ctl) & ACTIVE) != 0)
break;
else if (c == DISABLED || (e = executor) == null)
return -1;
else if (demand == 0L || tail == head)
break;
else if (U.compareAndSwapInt(this, CTL, c, c | ACTIVE)) {
try {
e.execute(this);
break;
} catch (RuntimeException | Error ex) { // back out
do {} while ((c = ctl) >= 0 &&
(c & ACTIVE) != 0 &&
!U.compareAndSwapInt(this, CTL, c,
c & ~ACTIVE));
throw ex;
}
}
}
return 1;
}
/**
* Tries to create or expand buffer, then adds item if possible
*/
final int growAndAdd(Object[] oldArray, T item) {
int oldLen, newLen;
if (oldArray != null)
newLen = (oldLen = oldArray.length) << 1;
else if (ctl >= 0) {
oldLen = 0;
newLen = minCapacity;
}
else
return -1; // disabled
if (oldLen >= maxCapacity || newLen <= 0)
return 0; // cannot grow
Object[] newArray;
try {
newArray = new Object[newLen];
} catch (Throwable ex) { // try to cope with OOME
if (oldLen > 0) // avoid continuous failure
maxCapacity = oldLen;
return 0;
}
array = newArray;
int t = tail, oldMask = oldLen - 1, newMask = newLen - 1;
if (oldArray != null && oldMask >= 0 && newMask >= oldMask) {
for (int j = head; j != t; ++j) { // races with consumer
Object x;
int i = j & oldMask;
if ((x = oldArray[i]) != null &&
U.compareAndSwapObject(oldArray,
(((long)i) << ASHIFT) + ABASE,
x, null))
newArray[j & newMask] = x;
}
}
newArray[t & newMask] = item;
tail = t + 1;
return 1;
}
/**
* Spins/helps/blocks while offer returns 0
*/
final int submit(T item) {
int stat;
if ((stat = offer(item)) == 0) {
Thread thread = Thread.currentThread();
if ((thread instanceof ForkJoinWorkerThread) &&
((ForkJoinWorkerThread)thread).getPool() == executor) {
for (ForkJoinTask t;;) { // try helping
if ((t = ForkJoinTask.peekNextLocalTask()) == null ||
!(t instanceof BufferedSubscription))
break;
if (t.tryUnfork())
t.exec();
if ((stat = offer(item)) != 0)
break;
}
}
if (stat == 0) {
putItem = item;
timeout = 0L;
try {
ForkJoinPool.managedBlock(this);
} catch (InterruptedException ie) {
timeout = INTERRUPTED;
}
stat = putStat;
if (timeout < 0L)
Thread.currentThread().interrupt();
}
}
return stat;
}
/**
* Timeout version of offer
*/
final int offerNanos(T item, long nanos) {
int stat;
if ((stat = offer(item)) == 0 && nanos > 0L) {
Thread thread = Thread.currentThread();
if ((thread instanceof ForkJoinWorkerThread) &&
((ForkJoinWorkerThread)thread).getPool() == executor) {
long deadline = System.nanoTime() + nanos;
for (ForkJoinTask t;;) { // similar to above
if ((t = ForkJoinTask.peekNextLocalTask()) == null ||
!(t instanceof BufferedSubscription))
break;
if (t.tryUnfork())
t.exec();
if ((stat = offer(item)) != 0 ||
(nanos = deadline - System.nanoTime()) <= 0L)
break;
}
}
if (stat == 0 && (timeout = nanos) > 0L) {
putItem = item;
try {
ForkJoinPool.managedBlock(this);
} catch (InterruptedException ie) {
timeout = INTERRUPTED;
}
stat = putStat;
if (timeout < 0L)
Thread.currentThread().interrupt();
}
}
return stat;
}
/**
* Nulls out most fields, mainly to avoid garbage retention
* until publisher unsubscribes, but also to help cleanly stop
* upon error by nulling required components.
*/
final void detach() {
pendingError = null;
subscriber = null;
executor = null;
array = null;
Thread w = waiter;
if (w != null) {
waiter = null;
LockSupport.unpark(w); // force wakeup
}
}
/**
* Issues error signal, asynchronously if a task is running,
* else synchronously
*/
final void onError(Throwable ex) {
for (int c;;) {
if ((c = ctl) == DISABLED)
break;
else if ((c & ACTIVE) != 0) {
pendingError = ex;
if (U.compareAndSwapInt(this, CTL, c, c | ERROR))
break; // cause consumer task to exit
}
else if (U.compareAndSwapInt(this, CTL, c, DISABLED)) {
Flow.Subscriber s = subscriber;
if (s != null && ex != null) {
try {
s.onError(ex);
} catch (Throwable ignore) {
}
}
detach();
break;
}
}
}
/**
* Tries to start consumer task upon a signal or request;
* disables on failure.
*/
final void startOrDisable() {
Executor e; // skip if already disabled
if ((e = executor) != null) {
try {
e.execute(this);
} catch (Throwable ex) { // back out and force signal
for (int c;;) {
if ((c = ctl) == DISABLED || (c & ACTIVE) == 0)
break;
if (U.compareAndSwapInt(this, CTL, c, c & ~ACTIVE)) {
onError(ex);
break;
}
}
}
}
}
final void onComplete() {
for (int c;;) {
if ((c = ctl) == DISABLED)
break;
if (U.compareAndSwapInt(this, CTL, c, c | (ACTIVE | COMPLETE))) {
if ((c & ACTIVE) == 0)
startOrDisable();
break;
}
}
}
final void onSubscribe() {
for (int c;;) {
if ((c = ctl) == DISABLED)
break;
if (U.compareAndSwapInt(this, CTL, c, c | (ACTIVE | SUBSCRIBE))) {
if ((c & ACTIVE) == 0)
startOrDisable();
break;
}
}
}
/**
* Causes consumer task to exit if active (without reporting
* onError unless there is already a pending error), and
* disables.
*/
public void cancel() {
for (int c;;) {
if ((c = ctl) == DISABLED)
break;
else if ((c & ACTIVE) != 0) {
if (U.compareAndSwapInt(this, CTL, c, c | ERROR))
break;
}
else if (U.compareAndSwapInt(this, CTL, c, DISABLED)) {
detach();
break;
}
}
}
/**
* Adds to demand and possibly starts task.
*/
public void request(long n) {
if (n > 0L) {
for (;;) {
long prev = demand, d;
if ((d = prev + n) < prev) // saturate
d = Long.MAX_VALUE;
if (U.compareAndSwapLong(this, DEMAND, prev, d)) {
for (int c, h;;) {
if (((c = ctl) & (ACTIVE | DISABLED)) != 0 ||
demand == 0L)
break;
if ((h = head) != tail) {
if (U.compareAndSwapInt(this, CTL, c,
c | ACTIVE)) {
startOrDisable();
break;
}
}
else if (head == h && tail == h)
break;
}
break;
}
}
}
else if (n < 0L)
onError(new IllegalArgumentException(
"negative subscription request"));
}
public final boolean isReleasable() { // for ManagedBlocker
T item = putItem;
if (item != null) {
if ((putStat = offer(item)) == 0)
return false;
putItem = null;
}
return true;
}
public final boolean block() { // for ManagedBlocker
T item = putItem;
if (item != null) {
putItem = null;
long nanos = timeout;
long deadline = (nanos > 0L) ? System.nanoTime() + nanos : 0L;
while ((putStat = offer(item)) == 0) {
if (Thread.interrupted()) {
timeout = INTERRUPTED;
if (nanos > 0L)
break;
}
else if (nanos > 0L &&
(nanos = deadline - System.nanoTime()) <= 0L)
break;
else if (waiter == null)
waiter = Thread.currentThread();
else {
if (nanos > 0L)
LockSupport.parkNanos(this, nanos);
else
LockSupport.park(this);
waiter = null;
}
}
}
waiter = null;
return true;
}
/**
* Consumer task loop; supports resubmission when used as
* ForkJoinTask.
*/
public final boolean exec() {
Flow.Subscriber s;
if ((s = subscriber) != null) { // else disabled
for (;;) {
long d = demand; // read volatile fields in acceptable order
int c = ctl;
int h = head;
int t = tail;
Object[] a = array;
int i, n; Object x; Thread w;
if ((c & (ERROR | SUBSCRIBE | DISABLED)) != 0) {
if ((c & ERROR) != 0) {
Throwable ex = pendingError;
ctl = DISABLED; // no need for CAS
if (ex != null) {
try {
s.onError(ex);
} catch (Throwable ignore) {
}
}
}
else if ((c & SUBSCRIBE) != 0) {
if (U.compareAndSwapInt(this, CTL, c,
c & ~SUBSCRIBE)) {
try {
s.onSubscribe(this);
} catch (Throwable ex) {
ctl = DISABLED;
}
}
}
else {
detach();
break;
}
}
else if (h == t) { // empty
if (h == tail &&
U.compareAndSwapInt(this, CTL, c, c &= ~ACTIVE)) {
if (h != tail || c != (c = ctl)) { // recheck
if ((c & (ACTIVE | DISABLED)) != 0 ||
!U.compareAndSwapInt(this, CTL, c,
c | ACTIVE))
break;
}
else if ((c & COMPLETE) != 0) {
ctl = DISABLED;
try {
s.onComplete();
} catch (Throwable ignore) {
}
}
else
break;
}
}
else if (a == null || (n = a.length) == 0 ||
(x = a[i = h & (n - 1)]) == null)
; // stale; retry
else if (d == 0L) { // can't take
if (demand == 0L &&
U.compareAndSwapInt(this, CTL, c, c &= ~ACTIVE) &&
((demand == 0L && c == (c = ctl)) || // recheck
(c & (ACTIVE | DISABLED)) != 0 ||
!U.compareAndSwapInt(this, CTL, c, c | ACTIVE)))
break;
}
else if (U.compareAndSwapObject(
a, (((long)i) << ASHIFT) + ABASE, x, null)) {
U.putOrderedInt(this, HEAD, h + 1);
while (!U.compareAndSwapLong(this, DEMAND, d, d - 1L))
d = demand; // almost never fails
if ((w = waiter) != null) {
waiter = null;
LockSupport.unpark(w); // release producer
}
try {
@SuppressWarnings("unchecked") T y = (T) x;
s.onNext(y);
} catch (Throwable ex) { // disable on throw
ctl = DISABLED;
}
}
}
}
return false; // resubmittable; never joined
}
// Runnable and FJ support
public final void run() { exec(); }
public final Void getRawResult() { return null; }
public final void setRawResult(Void v) {}
// Unsafe mechanics
private static final sun.misc.Unsafe U = sun.misc.Unsafe.getUnsafe();
private static final long CTL;
private static final long TAIL;
private static final long HEAD;
private static final long DEMAND;
private static final int ABASE;
private static final int ASHIFT;
static {
try {
CTL = U.objectFieldOffset
(BufferedSubscription.class.getDeclaredField("ctl"));
TAIL = U.objectFieldOffset
(BufferedSubscription.class.getDeclaredField("tail"));
HEAD = U.objectFieldOffset
(BufferedSubscription.class.getDeclaredField("head"));
DEMAND = U.objectFieldOffset
(BufferedSubscription.class.getDeclaredField("demand"));
ABASE = U.arrayBaseOffset(Object[].class);
int scale = U.arrayIndexScale(Object[].class);
if ((scale & (scale - 1)) != 0)
throw new Error("data type scale not a power of two");
ASHIFT = 31 - Integer.numberOfLeadingZeros(scale);
} catch (ReflectiveOperationException e) {
throw new Error(e);
}
}
}
}