[HARMONY-6663] Time-consuming operation with lock held in ServerSocketChannelImpl.java

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Won't Fix
• Affects Version/s: 6.0M1
• Component/s: Classlib
• Environment: Windows XP
• Assignee: Unassigned
• Reporter: Wendy Feng
• Created: 28/Sep/10 04:54
• Updated: 28/Sep/10 05:19
• Resolved: 28/Sep/10 05:19

Description

I found a time-consuming operation with lock held in modules/nio/src/main/java/common/org/apache/harmony/nio/internal/ServerSocketChannelImpl.java

public SocketChannel accept() throws IOException {
...
synchronized (acceptLock) {
boolean isBlocking = isBlocking();
...
do {
try

{ ((ServerSocketAdapter) socket).accept(socketGot, (SocketChannelImpl) sockChannel); // select successfully, break out immediately. break; } catch (SocketTimeoutException e) { // continue to accept if the channel is in blocking // mode. }
} while (isBlocking);
}
...
}

Thread A executes accept() method, holds a lock on "acceptLock ", but may block at socket.accept() for a long time.
Thread B executes accept(), cannot acquire the lock on "acceptLock ".

Consequence:
Lock contends, significantly downgrade software performance.

I suggest to move the do-while block out of the synchronization block as follow:
public SocketChannel accept() throws IOException {
...
boolean isBlocking = isBlocking();
synchronized (acceptLock) { ... }
do {
try { ((ServerSocketAdapter) socket).accept(socketGot, (SocketChannelImpl) sockChannel); // select successfully, break out immediately. break; }

catch (SocketTimeoutException e)

{ // continue to accept if the channel is in blocking // mode. }

} while (isBlocking);

...
}