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  • Tomcat 7 taking ages to start up after upgrade

    - by Lawrence
    I recently updated my server installation from Tomcat 6 to Tomcat 7, in order to take advantage of better connection pooling. My project uses Hibernate, for object persistance, a Mysql 5.5.20 database, and memcached for caching. When I was using Tomcat 6, Tomcat would start in about 8 seconds. After moving to Tomcat 7, it now takes between 75 - 80 seconds to start (this is on a Macbook pro 15", core i7 2Ghz, 8Gb of RAM). The only thing that has really changed between during the move from Tomcat 6 to 7 has been my context.xml file, which controls the connection pooling information: <Context antiJARLocking="true" reloadable="true" path=""> <Resource name="jdbc/test-db" auth="Container" type="javax.sql.DataSource" factory="org.apache.tomcat.jdbc.pool.DataSourceFactory" testOnBorrow="true" testOnReturn="false" testWhileIdle="true" validationQuery="SELECT 1" validationQueryTimeout="20000" validationInterval="30000" timeBetweenEvictionRunsMillis="60000" logValidationErrors="true" autoReconnect="true" username="webuser" password="xxxxxxx" driverClassName="com.mysql.jdbc.Driver" url="jdbc:mysql://databasename.us-east-1.rds.amazonaws.com:3306/test-db" maxActive="15" minIdle="2" maxIdle="10" maxWait="10000" maxAge="7200000"/> </Context> Now, as you can see, the database is running on Amazon RDS (where our live servers are), and thus is about 200ms round trip time away from my machine. I have already checked that I have security permissions to that database from my machine, (and anyway, it connects after 75 secs, so it cant be that). My initial thought was that Tomcat 7 and hibernate are doing something weird (like pre-instantiating a bunch of connections or something), and the latency to the database is amplifying the effects. While trying to diagnose the problem, I used jstack to get a stack trace of the Tomcat 7 server while its doing its startup thing. Here is the stack trace... Full thread dump Java HotSpot(TM) 64-Bit Server VM (20.12-b01-434 mixed mode): "Attach Listener" daemon prio=9 tid=7fa4c0038800 nid=0x10c39a000 waiting on condition [00000000] java.lang.Thread.State: RUNNABLE "Abandoned connection cleanup thread" daemon prio=5 tid=7fa4bb810000 nid=0x10f3ba000 in Object.wait() [10f3b9000] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <7f40a0070> (a java.lang.ref.ReferenceQueue$Lock) at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:118) - locked <7f40a0070> (a java.lang.ref.ReferenceQueue$Lock) at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:134) at com.mysql.jdbc.NonRegisteringDriver$1.run(NonRegisteringDriver.java:93) "PoolCleaner[545768040:1352724902327]" daemon prio=5 tid=7fa4be852800 nid=0x10e772000 in Object.wait() [10e771000] java.lang.Thread.State: TIMED_WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <7f40c7c90> (a java.util.TaskQueue) at java.util.TimerThread.mainLoop(Timer.java:509) - locked <7f40c7c90> (a java.util.TaskQueue) at java.util.TimerThread.run(Timer.java:462) "localhost-startStop-1" daemon prio=5 tid=7fa4bd034800 nid=0x10d66b000 runnable [10d668000] java.lang.Thread.State: RUNNABLE at java.net.SocketInputStream.socketRead0(Native Method) at java.net.SocketInputStream.read(SocketInputStream.java:129) at com.mysql.jdbc.util.ReadAheadInputStream.fill(ReadAheadInputStream.java:114) at com.mysql.jdbc.util.ReadAheadInputStream.readFromUnderlyingStreamIfNecessary(ReadAheadInputStream.java:161) at com.mysql.jdbc.util.ReadAheadInputStream.read(ReadAheadInputStream.java:189) - locked <7f3673be0> (a com.mysql.jdbc.util.ReadAheadInputStream) at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:3014) at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3467) at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3456) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3997) at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2468) at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2629) at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2713) - locked <7f366a1c0> (a com.mysql.jdbc.JDBC4Connection) at com.mysql.jdbc.ConnectionImpl.configureClientCharacterSet(ConnectionImpl.java:1930) at com.mysql.jdbc.ConnectionImpl.initializePropsFromServer(ConnectionImpl.java:3571) at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2445) at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2215) - locked <7f366a1c0> (a com.mysql.jdbc.JDBC4Connection) at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:813) at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47) at sun.reflect.GeneratedConstructorAccessor10.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27) at java.lang.reflect.Constructor.newInstance(Constructor.java:513) at com.mysql.jdbc.Util.handleNewInstance(Util.java:411) at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:399) at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:334) at org.apache.tomcat.jdbc.pool.PooledConnection.connectUsingDriver(PooledConnection.java:278) at org.apache.tomcat.jdbc.pool.PooledConnection.connect(PooledConnection.java:182) at org.apache.tomcat.jdbc.pool.ConnectionPool.createConnection(ConnectionPool.java:699) at org.apache.tomcat.jdbc.pool.ConnectionPool.borrowConnection(ConnectionPool.java:631) at org.apache.tomcat.jdbc.pool.ConnectionPool.init(ConnectionPool.java:485) at org.apache.tomcat.jdbc.pool.ConnectionPool.<init>(ConnectionPool.java:143) at org.apache.tomcat.jdbc.pool.DataSourceProxy.pCreatePool(DataSourceProxy.java:116) - locked <7f34f0dc8> (a org.apache.tomcat.jdbc.pool.DataSource) at org.apache.tomcat.jdbc.pool.DataSourceProxy.createPool(DataSourceProxy.java:103) at org.apache.tomcat.jdbc.pool.DataSourceFactory.createDataSource(DataSourceFactory.java:539) at org.apache.tomcat.jdbc.pool.DataSourceFactory.getObjectInstance(DataSourceFactory.java:237) at org.apache.naming.factory.ResourceFactory.getObjectInstance(ResourceFactory.java:143) at javax.naming.spi.NamingManager.getObjectInstance(NamingManager.java:304) at org.apache.naming.NamingContext.lookup(NamingContext.java:843) at org.apache.naming.NamingContext.lookup(NamingContext.java:154) at org.apache.naming.NamingContext.lookup(NamingContext.java:831) at org.apache.naming.NamingContext.lookup(NamingContext.java:168) at org.apache.catalina.core.NamingContextListener.addResource(NamingContextListener.java:1061) at org.apache.catalina.core.NamingContextListener.createNamingContext(NamingContextListener.java:671) at org.apache.catalina.core.NamingContextListener.lifecycleEvent(NamingContextListener.java:270) at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:119) at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:90) at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5173) - locked <7f46b07f0> (a org.apache.catalina.core.StandardContext) at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150) - locked <7f46b07f0> (a org.apache.catalina.core.StandardContext) at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1559) at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1549) at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303) at java.util.concurrent.FutureTask.run(FutureTask.java:138) at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) at java.lang.Thread.run(Thread.java:680) "Catalina-startStop-1" daemon prio=5 tid=7fa4b7a5e800 nid=0x10d568000 waiting on condition [10d567000] java.lang.Thread.State: WAITING (parking) at sun.misc.Unsafe.park(Native Method) - parking to wait for <7f480e970> (a java.util.concurrent.FutureTask$Sync) at java.util.concurrent.locks.LockSupport.park(LockSupport.java:156) at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:811) at java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireSharedInterruptibly(AbstractQueuedSynchronizer.java:969) at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly(AbstractQueuedSynchronizer.java:1281) at java.util.concurrent.FutureTask$Sync.innerGet(FutureTask.java:218) at java.util.concurrent.FutureTask.get(FutureTask.java:83) at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:1123) - locked <7f453c630> (a org.apache.catalina.core.StandardHost) at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:800) - locked <7f453c630> (a org.apache.catalina.core.StandardHost) at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150) - locked <7f453c630> (a org.apache.catalina.core.StandardHost) at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1559) at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1549) at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303) at java.util.concurrent.FutureTask.run(FutureTask.java:138) at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) at java.lang.Thread.run(Thread.java:680) "GC Daemon" daemon prio=2 tid=7fa4b9912800 nid=0x10d465000 in Object.wait() [10d464000] java.lang.Thread.State: TIMED_WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <7f4506d28> (a sun.misc.GC$LatencyLock) at sun.misc.GC$Daemon.run(GC.java:100) - locked <7f4506d28> (a sun.misc.GC$LatencyLock) "Low Memory Detector" daemon prio=5 tid=7fa4b480b800 nid=0x10c8ae000 runnable [00000000] java.lang.Thread.State: RUNNABLE "C2 CompilerThread1" daemon prio=9 tid=7fa4b480b000 nid=0x10c7ab000 waiting on condition [00000000] java.lang.Thread.State: RUNNABLE "C2 CompilerThread0" daemon prio=9 tid=7fa4b480a000 nid=0x10c6a8000 waiting on condition [00000000] java.lang.Thread.State: RUNNABLE "Signal Dispatcher" daemon prio=9 tid=7fa4b4809800 nid=0x10c5a5000 runnable [00000000] java.lang.Thread.State: RUNNABLE "Surrogate Locker Thread (Concurrent GC)" daemon prio=5 tid=7fa4b4808800 nid=0x10c4a2000 waiting on condition [00000000] java.lang.Thread.State: RUNNABLE "Finalizer" daemon prio=8 tid=7fa4b793f000 nid=0x10c297000 in Object.wait() [10c296000] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <7f451c8f0> (a java.lang.ref.ReferenceQueue$Lock) at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:118) - locked <7f451c8f0> (a java.lang.ref.ReferenceQueue$Lock) at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:134) at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:159) "Reference Handler" daemon prio=10 tid=7fa4b793e000 nid=0x10c194000 in Object.wait() [10c193000] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <7f452e168> (a java.lang.ref.Reference$Lock) at java.lang.Object.wait(Object.java:485) at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:116) - locked <7f452e168> (a java.lang.ref.Reference$Lock) "main" prio=5 tid=7fa4b7800800 nid=0x104329000 waiting on condition [104327000] java.lang.Thread.State: WAITING (parking) at sun.misc.Unsafe.park(Native Method) - parking to wait for <7f480e9a0> (a java.util.concurrent.FutureTask$Sync) at java.util.concurrent.locks.LockSupport.park(LockSupport.java:156) at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:811) at java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireSharedInterruptibly(AbstractQueuedSynchronizer.java:969) at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly(AbstractQueuedSynchronizer.java:1281) at java.util.concurrent.FutureTask$Sync.innerGet(FutureTask.java:218) at java.util.concurrent.FutureTask.get(FutureTask.java:83) at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:1123) - locked <7f451fd90> (a org.apache.catalina.core.StandardEngine) at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:302) - locked <7f451fd90> (a org.apache.catalina.core.StandardEngine) at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150) - locked <7f451fd90> (a org.apache.catalina.core.StandardEngine) at org.apache.catalina.core.StandardService.startInternal(StandardService.java:443) - locked <7f451fd90> (a org.apache.catalina.core.StandardEngine) at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150) - locked <7f453e810> (a org.apache.catalina.core.StandardService) at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:732) - locked <7f4506d58> (a [Lorg.apache.catalina.Service;) at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150) - locked <7f44f7ba0> (a org.apache.catalina.core.StandardServer) at org.apache.catalina.startup.Catalina.start(Catalina.java:684) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:322) at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:451) "VM Thread" prio=9 tid=7fa4b7939800 nid=0x10c091000 runnable "Gang worker#0 (Parallel GC Threads)" prio=9 tid=7fa4b7802000 nid=0x10772b000 runnable "Gang worker#1 (Parallel GC Threads)" prio=9 tid=7fa4b7802800 nid=0x10782e000 runnable "Gang worker#2 (Parallel GC Threads)" prio=9 tid=7fa4b7803000 nid=0x107931000 runnable "Gang worker#3 (Parallel GC Threads)" prio=9 tid=7fa4b7804000 nid=0x107a34000 runnable "Gang worker#4 (Parallel GC Threads)" prio=9 tid=7fa4b7804800 nid=0x107b37000 runnable "Gang worker#5 (Parallel GC Threads)" prio=9 tid=7fa4b7805000 nid=0x107c3a000 runnable "Gang worker#6 (Parallel GC Threads)" prio=9 tid=7fa4b7805800 nid=0x107d3d000 runnable "Gang worker#7 (Parallel GC Threads)" prio=9 tid=7fa4b7806800 nid=0x107e40000 runnable "Concurrent Mark-Sweep GC Thread" prio=9 tid=7fa4b78e3800 nid=0x10bd0b000 runnable "Gang worker#0 (Parallel CMS Threads)" prio=9 tid=7fa4b78e2800 nid=0x10b305000 runnable "Gang worker#1 (Parallel CMS Threads)" prio=9 tid=7fa4b78e3000 nid=0x10b408000 runnable "VM Periodic Task Thread" prio=10 tid=7fa4b4815800 nid=0x10c9b1000 waiting on condition "Exception Catcher Thread" prio=10 tid=7fa4b7801800 nid=0x104554000 runnable JNI global references: 919 The only thing I can figure out from this is that it looks like the mysql jdbc drivers might have something to do with the long start up (the various stack traces I took during the start up process all pretty much look the same as this). Could anyone shed some light on what might be causing this? Have I done something dense in my context.xml? Is hibernate perhaps to blame?

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  • Inside the Concurrent Collections: ConcurrentDictionary

    - by Simon Cooper
    Using locks to implement a thread-safe collection is rather like using a sledgehammer - unsubtle, easy to understand, and tends to make any other tool redundant. Unlike the previous two collections I looked at, ConcurrentStack and ConcurrentQueue, ConcurrentDictionary uses locks quite heavily. However, it is careful to wield locks only where necessary to ensure that concurrency is maximised. This will, by necessity, be a higher-level look than my other posts in this series, as there is quite a lot of code and logic in ConcurrentDictionary. Therefore, I do recommend that you have ConcurrentDictionary open in a decompiler to have a look at all the details that I skip over. The problem with locks There's several things to bear in mind when using locks, as encapsulated by the lock keyword in C# and the System.Threading.Monitor class in .NET (if you're unsure as to what lock does in C#, I briefly covered it in my first post in the series): Locks block threads The most obvious problem is that threads waiting on a lock can't do any work at all. No preparatory work, no 'optimistic' work like in ConcurrentQueue and ConcurrentStack, nothing. It sits there, waiting to be unblocked. This is bad if you're trying to maximise concurrency. Locks are slow Whereas most of the methods on the Interlocked class can be compiled down to a single CPU instruction, ensuring atomicity at the hardware level, taking out a lock requires some heavy lifting by the CLR and the operating system. There's quite a bit of work required to take out a lock, block other threads, and wake them up again. If locks are used heavily, this impacts performance. Deadlocks When using locks there's always the possibility of a deadlock - two threads, each holding a lock, each trying to aquire the other's lock. Fortunately, this can be avoided with careful programming and structured lock-taking, as we'll see. So, it's important to minimise where locks are used to maximise the concurrency and performance of the collection. Implementation As you might expect, ConcurrentDictionary is similar in basic implementation to the non-concurrent Dictionary, which I studied in a previous post. I'll be using some concepts introduced there, so I recommend you have a quick read of it. So, if you were implementing a thread-safe dictionary, what would you do? The naive implementation is to simply have a single lock around all methods accessing the dictionary. This would work, but doesn't allow much concurrency. Fortunately, the bucketing used by Dictionary allows a simple but effective improvement to this - one lock per bucket. This allows different threads modifying different buckets to do so in parallel. Any thread making changes to the contents of a bucket takes the lock for that bucket, ensuring those changes are thread-safe. The method that maps each bucket to a lock is the GetBucketAndLockNo method: private void GetBucketAndLockNo( int hashcode, out int bucketNo, out int lockNo, int bucketCount) { // the bucket number is the hashcode (without the initial sign bit) // modulo the number of buckets bucketNo = (hashcode & 0x7fffffff) % bucketCount; // and the lock number is the bucket number modulo the number of locks lockNo = bucketNo % m_locks.Length; } However, this does require some changes to how the buckets are implemented. The 'implicit' linked list within a single backing array used by the non-concurrent Dictionary adds a dependency between separate buckets, as every bucket uses the same backing array. Instead, ConcurrentDictionary uses a strict linked list on each bucket: This ensures that each bucket is entirely separate from all other buckets; adding or removing an item from a bucket is independent to any changes to other buckets. Modifying the dictionary All the operations on the dictionary follow the same basic pattern: void AlterBucket(TKey key, ...) { int bucketNo, lockNo; 1: GetBucketAndLockNo( key.GetHashCode(), out bucketNo, out lockNo, m_buckets.Length); 2: lock (m_locks[lockNo]) { 3: Node headNode = m_buckets[bucketNo]; 4: Mutate the node linked list as appropriate } } For example, when adding another entry to the dictionary, you would iterate through the linked list to check whether the key exists already, and add the new entry as the head node. When removing items, you would find the entry to remove (if it exists), and remove the node from the linked list. Adding, updating, and removing items all follow this pattern. Performance issues There is a problem we have to address at this point. If the number of buckets in the dictionary is fixed in the constructor, then the performance will degrade from O(1) to O(n) when a large number of items are added to the dictionary. As more and more items get added to the linked lists in each bucket, the lookup operations will spend most of their time traversing a linear linked list. To fix this, the buckets array has to be resized once the number of items in each bucket has gone over a certain limit. (In ConcurrentDictionary this limit is when the size of the largest bucket is greater than the number of buckets for each lock. This check is done at the end of the TryAddInternal method.) Resizing the bucket array and re-hashing everything affects every bucket in the collection. Therefore, this operation needs to take out every lock in the collection. Taking out mutiple locks at once inevitably summons the spectre of the deadlock; two threads each hold a lock, and each trying to acquire the other lock. How can we eliminate this? Simple - ensure that threads never try to 'swap' locks in this fashion. When taking out multiple locks, always take them out in the same order, and always take out all the locks you need before starting to release them. In ConcurrentDictionary, this is controlled by the AcquireLocks, AcquireAllLocks and ReleaseLocks methods. Locks are always taken out and released in the order they are in the m_locks array, and locks are all released right at the end of the method in a finally block. At this point, it's worth pointing out that the locks array is never re-assigned, even when the buckets array is increased in size. The number of locks is fixed in the constructor by the concurrencyLevel parameter. This simplifies programming the locks; you don't have to check if the locks array has changed or been re-assigned before taking out a lock object. And you can be sure that when a thread takes out a lock, another thread isn't going to re-assign the lock array. This would create a new series of lock objects, thus allowing another thread to ignore the existing locks (and any threads controlling them), breaking thread-safety. Consequences of growing the array Just because we're using locks doesn't mean that race conditions aren't a problem. We can see this by looking at the GrowTable method. The operation of this method can be boiled down to: private void GrowTable(Node[] buckets) { try { 1: Acquire first lock in the locks array // this causes any other thread trying to take out // all the locks to block because the first lock in the array // is always the one taken out first // check if another thread has already resized the buckets array // while we were waiting to acquire the first lock 2: if (buckets != m_buckets) return; 3: Calculate the new size of the backing array 4: Node[] array = new array[size]; 5: Acquire all the remaining locks 6: Re-hash the contents of the existing buckets into array 7: m_buckets = array; } finally { 8: Release all locks } } As you can see, there's already a check for a race condition at step 2, for the case when the GrowTable method is called twice in quick succession on two separate threads. One will successfully resize the buckets array (blocking the second in the meantime), when the second thread is unblocked it'll see that the array has already been resized & exit without doing anything. There is another case we need to consider; looking back at the AlterBucket method above, consider the following situation: Thread 1 calls AlterBucket; step 1 is executed to get the bucket and lock numbers. Thread 2 calls GrowTable and executes steps 1-5; thread 1 is blocked when it tries to take out the lock in step 2. Thread 2 re-hashes everything, re-assigns the buckets array, and releases all the locks (steps 6-8). Thread 1 is unblocked and continues executing, but the calculated bucket and lock numbers are no longer valid. Between calculating the correct bucket and lock number and taking out the lock, another thread has changed where everything is. Not exactly thread-safe. Well, a similar problem was solved in ConcurrentStack and ConcurrentQueue by storing a local copy of the state, doing the necessary calculations, then checking if that state is still valid. We can use a similar idea here: void AlterBucket(TKey key, ...) { while (true) { Node[] buckets = m_buckets; int bucketNo, lockNo; GetBucketAndLockNo( key.GetHashCode(), out bucketNo, out lockNo, buckets.Length); lock (m_locks[lockNo]) { // if the state has changed, go back to the start if (buckets != m_buckets) continue; Node headNode = m_buckets[bucketNo]; Mutate the node linked list as appropriate } break; } } TryGetValue and GetEnumerator And so, finally, we get onto TryGetValue and GetEnumerator. I've left these to the end because, well, they don't actually use any locks. How can this be? Whenever you change a bucket, you need to take out the corresponding lock, yes? Indeed you do. However, it is important to note that TryGetValue and GetEnumerator don't actually change anything. Just as immutable objects are, by definition, thread-safe, read-only operations don't need to take out a lock because they don't change anything. All lockless methods can happily iterate through the buckets and linked lists without worrying about locking anything. However, this does put restrictions on how the other methods operate. Because there could be another thread in the middle of reading the dictionary at any time (even if a lock is taken out), the dictionary has to be in a valid state at all times. Every change to state has to be made visible to other threads in a single atomic operation (all relevant variables are marked volatile to help with this). This restriction ensures that whatever the reading threads are doing, they never read the dictionary in an invalid state (eg items that should be in the collection temporarily removed from the linked list, or reading a node that has had it's key & value removed before the node itself has been removed from the linked list). Fortunately, all the operations needed to change the dictionary can be done in that way. Bucket resizes are made visible when the new array is assigned back to the m_buckets variable. Any additions or modifications to a node are done by creating a new node, then splicing it into the existing list using a single variable assignment. Node removals are simply done by re-assigning the node's m_next pointer. Because the dictionary can be changed by another thread during execution of the lockless methods, the GetEnumerator method is liable to return dirty reads - changes made to the dictionary after GetEnumerator was called, but before the enumeration got to that point in the dictionary. It's worth listing at this point which methods are lockless, and which take out all the locks in the dictionary to ensure they get a consistent view of the dictionary: Lockless: TryGetValue GetEnumerator The indexer getter ContainsKey Takes out every lock (lockfull?): Count IsEmpty Keys Values CopyTo ToArray Concurrent principles That covers the overall implementation of ConcurrentDictionary. I haven't even begun to scratch the surface of this sophisticated collection. That I leave to you. However, we've looked at enough to be able to extract some useful principles for concurrent programming: Partitioning When using locks, the work is partitioned into independant chunks, each with its own lock. Each partition can then be modified concurrently to other partitions. Ordered lock-taking When a method does need to control the entire collection, locks are taken and released in a fixed order to prevent deadlocks. Lockless reads Read operations that don't care about dirty reads don't take out any lock; the rest of the collection is implemented so that any reading thread always has a consistent view of the collection. That leads us to the final collection in this little series - ConcurrentBag. Lacking a non-concurrent analogy, it is quite different to any other collection in the class libraries. Prepare your thinking hats!

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  • Ubuntu 12.04 lightdm dumps to tty. Cannot start GUI interface when booting off harddrive, but can when booting off usb

    - by user72681
    When booting, lightdm dumps to tty. No GUI interface works- this is after a fresh install of Ubuntu 12.04 where the GUI interface works when running off the USB. I have an NVIDIA Corporation G98 [Quadro NVS 420] graphics card. After I call startx from the terminal it still doesn't work. I get the following in the Xorg.0.log: [ 327.718] (--) NVIDIA(0): Memory: 262144 kBytes [ 327.718] (--) NVIDIA(0): VideoBIOS: 62.98.6f.00.07 [ 327.718] (II) NVIDIA(0): Detected PCI Express Link width: 16X [ 327.718] (--) NVIDIA(0): Interlaced video modes are supported on this GPU [ 327.756] (--) NVIDIA(0): Connected display device(s) on Quadro NVS 420 at PCI:3:0:0 [ 327.756] (--) NVIDIA(0): none [ 327.756] (EE) NVIDIA(0): No display devices found for this X screen. [ 328.010] (II) UnloadModule: "nvidia" [ 328.010] (II) Unloading nvidia [ 328.010] (II) UnloadModule: "wfb" [ 328.010] (II) Unloading wfb [ 328.010] (II) UnloadModule: "fb" [ 328.010] (II) Unloading fb [ 328.011] (EE) Screen(s) found, but none have a usable configuration. [ 328.011] Fatal server error: [ 328.011] no screens found /var/log/lightdm/lightdm.log [+0.00s] DEBUG: Starting local X display [+0.00s] DEBUG: X server :0 will replace Plymouth [+0.02s] DEBUG: Using VT 7 [+0.02s] DEBUG: Activating VT 7 [+0.02s] DEBUG: Logging to /var/log/lightdm/x-0.log [+0.02s] DEBUG: Writing X server authority to /var/run/lightdm/root/:0 [+0.02s] DEBUG: Launching X Server [+0.02s] DEBUG: Launching process 1074: /usr/bin/X :0 -auth /var/run/lightdm/root/:0 -nolisten tcp vt7 -novtswitch -background none [+0.02s] DEBUG: Waiting for ready signal from X server :0 [+0.02s] DEBUG: Acquired bus name org.freedesktop.DisplayManager [+0.02s] DEBUG: Registering seat with bus path /org/freedesktop/DisplayManager/Seat0 [+1.38s] DEBUG: Process 1074 exited with return value 1 [+1.38s] DEBUG: X server stopped [+1.38s] DEBUG: Removing X server authority /var/run/lightdm/root/:0 [+1.38s] DEBUG: Releasing VT 7 [+1.38s] DEBUG: Stopping Plymouth, X server failed to start [+1.39s] DEBUG: Display server stopped [+1.39s] DEBUG: Stopping display [+1.39s] DEBUG: Display stopped [+1.39s] DEBUG: Stopping X local seat, failed to start a display [+1.39s] DEBUG: Stopping seat [+1.39s] DEBUG: Seat stopped [+1.39s] DEBUG: Required seat has stopped [+1.39s] DEBUG: Stopping display manager [+1.39s] DEBUG: Display manager stopped [+1.39s] DEBUG: Stopping daemon [+1.39s] DEBUG: Exiting with return value 1 /var/log/lightdm/x-0.log X Protocol Version 11, Revision 0 Build Operating System: Linux 2.6.24-31-server x86_64 Ubuntu Current Operating System: Linux oorn 3.2.0-23-generic #36-Ubuntu SMP Tue Apr 10 20:39:51 UTC 2012 x86_64 Kernel command line: BOOT_IMAGE=/boot/vmlinuz-3.2.0-23-generic root=UUID=b25ab072-077d-40f1-95a4-c7fd66acd2f0 ro reboot=pci quiet splash vt.handoff=7 Build Date: 07 May 2012 11:43:21PM xorg-server 2:1.11.4-0ubuntu10.2 (For technical support please see http://www.ubuntu.com/support) Current version of pixman: 0.24.4 Before reporting problems, check http://wiki.x.org to make sure that you have the latest version. Markers: (--) probed, (**) from config file, (==) default setting, (++) from command line, (!!) notice, (II) informational, (WW) warning, (EE) error, (NI) not implemented, (??) unknown. (==) Log file: "/var/log/Xorg.0.log", Time: Wed Jun 27 12:51:45 2012 (==) Using config file: "/etc/X11/xorg.conf" (==) Using system config directory "/usr/share/X11/xorg.conf.d" (EE) NVIDIA(0): No display devices found for this X screen. (EE) Screen(s) found, but none have a usable configuration. Fatal server error: no screens found Please consult the The X.Org Foundation support at http://wiki.x.org for help. Please also check the log file at "/var/log/Xorg.0.log" for additional information. ddxSigGiveUp: Closing log Server terminated with error (1). Closing log file.

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  • How to change I/O priority of a process or thread in Win7?

    - by romkyns
    Process Explorer is able to show the effective IO priority of a given thread, but not change it. Seeing as IO priority support is a comparatively new feature, most programs don't set their own IO priorities. It appears that by default the IO priority is derived from the thread priority (rather than process priority), which Process Explorer can't modify either. Are there any other tools out there that can help me change the IO priority of a given thread / all threads of a given process?

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  • Why should most logic be in the monitor objects and not in the thread objects when writing concurrent software in Java?

    - by refuser
    When I took the Realtime and Concurrent programming course our lecturer told us that when writing concurrent programs in Java and using monitors, most of the logic should be in the monitor and as little as possible in the threads that access it. I never really understood why and I really would like to. Let me clarify. In this particular case we had several classes. Lift extends Thread Person extends Thread LiftView Monitor, all methods synchronized. This is nothing we came up with, our task was to implement a lift simulation with persons waiting on different floors, and theses were the class skeletons that were given. Then our lecturer said to implement most of the logic in the monitor (he was talking about class Monitor as THE monitor) and as little as possible in the threads. Why would he make a statement like that?

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  • Is there a quasi-standard set of attributes to annotate thread safety, immutability etc.?

    - by Eugene Beresovksy
    Except for a blog post here and there, describing the custom attributes someone created, but that do not seem to get any traction - like one describing how to enforce immutability, another one on Documenting Thread Safety, modeling the attributes after JCIP annotations - is there any standard emerging? Anything MS might be planning for the future? This is something that should be standard, if there's to be any chance of interoperability between libraries concurrency-wise. Both for documentation purposes, and also to feed static / dynamic test tools. If MS isn't doing anything in that direction, it could be done on CodePlex - but I couldn't find anything there, either. <opinion>Concurrency and thread safety are really hard in imperative and object-languages like C# and Java, we should try to tame it, until we hopefully switch to more appropriate languages.</opinion>

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  • MS-Outlook add-on to move a new message to the same folder as the rest of the thread

    - by Guss
    I'm forced to use MS-Outlook in my job, while I very much like the feature that shows all the messages of a discussion thread (that are stored in different folders) in the inbox when a new message is received for that thread, if the previous messages are in a different data file (which I'm forced to have as the MS-Exchange server quota is very very small) then the message list only shows the name of the data file and not the name of the folder where the messages are stored. As a result, because I file my message by context (i.e. all the emails for project A go into a "Project A" folder, etc), and its important for me to have all the messages in a single thread in the same folder, it is sometimes hard to figure out into which folder should I file the new message. It would be great help if there was some add-on or VBA script that I could add to my setup that will offer a shortcut key or a button to "file this message to the same folder as the previous messages in the conversation thread".

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  • how to serialize function depending on what instance of object calls it, if same instance call in a thread then do serialize else not

    - by LondonDreams
    I have a function which fetches and updates some record from db and I am trying to make sure each if the function is called by same instance of object(same Or different thread) then function should behave synchronized else its a call from different object instance function need not to be synchronized. I have tried it use a lock per client. That is, instead of synchronizing the method directly using explicit locking through lock objects using Map. function is like :- getAndUpdateMyHitCount(myObjId){ //go to db and get unique record by myObjId //fetch value , increment , save update } And this function may get call is same thread by different Or same object instance But as fetching and matching from Map is slow , Is there other optimized way to do this ? Found similar at this Question but dont feel that is optimized

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  • Capturing stdout from an imported module in wxpython and sending it to a textctrl, without blocking the GUI

    - by splafe
    There are alot of very similar questions to this but I can't find one that applies specifically to what I'm trying to do. I have a simulation (written in SimPy) that I'm writing a GUI for, the main output of the simulation is text - to the console from 'print' statements. Now, I thought the simplest way would be to create a seperate module GUI.py, and import my simulation program into it: import osi_model I want all the print statements to be captured by the GUI and appear inside a Textctrl, which there's countless examples of on here, along these lines: class MyFrame(wx.Frame): def __init__(self, *args, **kwds): <general frame initialisation stuff..> redir=RedirectText(self.txtCtrl_1) sys.stdout=redir class RedirectText: def __init__(self,aWxTextCtrl): self.out=aWxTextCtrl def write(self,string): self.out.WriteText(string) I am also starting my simulation from a 'Go' button: def go_btn_click(self, event): print 'GO' self.RT = threading.Thread(target=osi_model.RunThis()) self.RT.start() This all works fine, and the output from the simulation module is captured by the TextCtrl, except the GUI locks up and becomes unresponsive - I still need it to be accessible (at the very minimum to have a 'Stop' button). I'm not sure if this is a botched attempt at creating a new thread that I've done here, but I assume a new thread will be needed at some stage in this process. People suggest using wx.CallAfter, but I'm not sure how to go about this considering the imported module doesn't know about wx, and also I can't realistically go through the entire simulation architecture and change all the print statements to wx.CallAfter, and any attempt to capture the shell from inside the imported simulation program leads to the program crashing. Does anybody have any ideas about how I can best achieve this? So all I really need is for all console text to be captured by a TextCtrl while the GUI remains responsive, and all text is solely coming from an imported module. (Also, secondary question regarding a Stop button - is it bad form to just kill the simulation thread?). Thanks, Duncan

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  • what's best language to mate with Adobe Flex-based GUI for math crunching?

    - by gkdsp
    Hi, I'm not a software expert but need to outsource a web-based scientific GUI application, and I'm considering Adobe Flex. My math routines are currently in Javascript and C/C+. Having no experience with Flex, was hoping someone could help me understand what options are available for performing (preferably fast and efficient) CLIENT-side calculations. That is, can Flex interact with Javascript and/or C easily? If not, is actionscript or other language preferred? Downsides/tradeoffs? Need functions like LOG10, LN, SQRT, and would be nice to also have the error function (ERF) and complementary error function (ERFC), although I may be able to derive these last two from more basic functions if necessary. Thanks!

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  • How to set Ubuntu as wireless accespoint in the GUI way?

    - by Agmenor
    My aim is to make my Ubuntu machine be a wireless accesspoint using wifi. Of course I found two AskUbuntu questions already treating that; this one and that one. Nevertheless, as far as I am concerned I would like to set up such a network in the Graphical User Interface (GUI) way. Please avoid solutions with the command line. So a solution suggesting to use Network Manager would be really welcomed. Please name and describe very precisely each step, so I can easily find the equivalent in my own language. Thank you for your answers!

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  • How do I start the GUI (Window Manager?) over VNC?

    - by Maarx
    I have a netbook and a server, to both of which I installed the identical Ubuntu 10.04 LTS distribution. On the server, I had the foresight to install and enable the SSH server before disconnecting the monitor and keyboard and mouse. I then ssh'ed in and enabled the VNC server as well. Now I want the full server experience on the netbook, but when I VNC in, I am greeted with the displayed screen. (names have been redacted) How do I start the rest of the default Ubuntu GUI experience? (the toolbars at the top) ((is that the window manager?))

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  • As a Qt GUI programmer, how to improve (career & skill)?

    - by linjunhalida
    hello, I'm a python & Qt programmer, and my daily job is create small PC GUI programs ship with hardware devices. the problem is, My job is simple, read/write data to device by using serial port(pyserial), display and edit data(PyQt + PyQwt), that's all. although I'm a linux user, my program is running under windows XP, but thanks to PyQt, I can still develop under linux. And I'm always afraid of being replaced by the people cheaper and younger than me in the future. (I'm 26 now.. not too much time for playing..) So I need improve myself, and make me more competitive in the global market, and I like programming, and want coding till the end of my life. any roadmap suggestion?

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  • Help! GUI design tool for web & windows applications (2 replies)

    Hi All, We are currently looking to buy a Windows &amp; Web GUI design tool. Our company is doing softwares for Windows &amp; Web application with Visual Studio 2008. Our clients will be using this tool to build screenshots. Projects delivery should be faster with this tool. Do you have any suggestions ? Of course, a Microsoft Parter product is better... Thanks for your help! Simon Levesque Sonim6 Inc.

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  • What simple offline GUI database should I use for this application?

    - by gcc
    I am looking an open source application. Application should have : * database support ( create two or three table ) * GUI ( what I have created should be seen ) Example : Assume that I have created a table ; X_table : | A | B | C | D | After creating table, I am loading data | A | B | C | D | | 1 | 11 | b | f | - | 3 | 12 | a | o | - data | 4 | 13 | r | o | - When I am opening application not for loading data, I want see data in graphical interface. Are there any open source application which have above feature ? Application can be so simple, * no internet connection * support only one database * static table creation ( once created never changed ) Application can be run Ubuntu 12.04 and/or Windows. In other words, I am wanting database viewer and editor. EDIT: I should load pdf file, image etc. or give path of the file to the application. This link can be reference to my question . ( Interface should be like this, just a list )

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  • How to clean launch a GUI app via the Terminal (so it doesn't wait for termination)?

    - by Peter.O
    Some GUI apps launch cleanly via the Terminal command line. Some don't, and they cause the Terminal to wait for the app to terminate. ...and even then, some don't "release" the command line. The mysterious ampersand "&" suffix, seems to cause the terminal to put the process into the background... (but I'm not sure what happens there). Is there a way to launch an app via the Terminal, so that there is no "hang on" effect? ... just like launching something via F2. I'd like to have the command line available again, immediately (without something still in the background and writing out system message in the terminal).

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  • Help! GUI design tool for web & windows applications (2 replies)

    Hi All, We are currently looking to buy a Windows &amp; Web GUI design tool. Our company is doing softwares for Windows &amp; Web application with Visual Studio 2008. Our clients will be using this tool to build screenshots. Projects delivery should be faster with this tool. Do you have any suggestions ? Of course, a Microsoft Parter product is better... Thanks for your help! Simon Levesque Sonim6 Inc.

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  • Threads in WCF service

    - by dragonfly
    Hi, there is a piece of code: class WCFConsoleHostApp : IBank { private static int _instanceCounter; public WCFConsoleHostApp () { Interlocked.Increment(ref _instanceCounter); Console.WriteLine(string.Format("{0:T} Instance nr " + _instanceCounter + " created", DateTime.Now)); } private static int amount; static void Main(string[] args) { ServiceHost host = new ServiceHost(typeof(WCFConsoleHostApp)); host.Open(); Console.WriteLine("Host is running..."); Console.ReadLine(); } #region IBank Members BankOperationResult IBank.Put(int amount) { Console.WriteLine(string.Format("{0:00} {1}", Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread) + " Putting..."); WCFConsoleHostApp.amount += amount; Thread.Sleep(20000); Console.WriteLine(string.Format("{0:00} {1}", Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread) + " Putting done"); return new BankOperationResult { CurrentAmount = WCFConsoleHostApp.amount, Success = true }; } BankOperationResult IBank.Withdraw(int amount) { Console.WriteLine(string.Format("{0:00} {1}", Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread) + " Withdrawing..."); WCFConsoleHostApp.amount -= amount; Thread.Sleep(20000); Console.WriteLine(string.Format("{0:00} {1}", Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread) + " Withdrawing done"); return new BankOperationResult { CurrentAmount = WCFConsoleHostApp.amount, Success = true }; } #endregion } My test client application calls that service in 50 threads (service is PerCall). What I found very disturbing is when I added Thread.Sleep(20000) WCF creates one service instance per second using different thread from pool. When I remove Thread.Sleep(20000) 50 instances are instanciated straight away, and about 2-4 threads are used to do it - which in fact I consider normal. Could somebody explain why when Thread.Sleep causes those funny delays in creating instances?

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  • Perl cgi @INC different in shell and in http request

    - by pistacchio
    Hi to all, I have the follwing, simplest per cgi script: use strict; use warnings; use CGI(); use CGI::Carp qw(fatalsToBrowser); use Template; print CGI::header(); foreach(@INC) { print "$_\n"; } When called (http://[..]/cgi-bin/p.cgi) I am given the following error: Can't locate Template.pm in @INC (@INC contains: /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi /usr/lib/perl5/site_perl/5.8.8 /usr/lib/perl5/site_perl /usr/lib/perl5/vendor_perl/5.8.8/i386-linux-thread-multi /usr/lib/perl5/vendor_perl/5.8.8 /usr/lib/perl5/vendor_perl /usr/lib/perl5/5.8.8/i386-linux-thread-multi /usr/lib/perl5/5.8.8 .) at /home/pistacchio/webapps/htdocs/cgi-bin/p.cgi line 8. BEGIN failed--compilation aborted at /home/pistacchio/webapps/htdocs/cgi-bin/p.cgi line 8. I made sure that Template is installed and indeed when running this program from shell it works (loads Template) and outputs: Content-Type: text/html; charset=ISO-8859-1 /home/pistacchio/lib/perl5 /home/pistacchio/lib/perl5/lib/i386-linux-thread-multi /home/pistacchio/lib/perl5/lib /home/pistacchio/lib/perl5/lib/i386-linux-thread-multi /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi /usr/lib/perl5/site_perl/5.8.8 /usr/lib/perl5/site_perl /usr/lib/perl5/vendor_perl/5.8.8/i386-linux-thread-multi /usr/lib/perl5/vendor_perl/5.8.8 /usr/lib/perl5/vendor_perl /usr/lib/perl5/5.8.8/i386-linux-thread-multi /usr/lib/perl5/5.8.8 Template is installed in /home/pistacchio/lib/perl5/lib/i386-linux-thread-multi [pistacchio@web118 i386-linux-thread-multi]$ pwd /home/pistacchio/lib/perl5/lib/i386-linux-thread-multi [pistacchio@web118 i386-linux-thread-multi]$ ls auto perllocal.pod Template Template.pm This directory is correctly listed in env and, as previously posted, in @INC. In @INC it is shown twice, so I even tried to pop it out before calling use Template, but without result. From env: [pistacchio@web118 i386-linux-thread-multi]$ env [..] PERL5LIB=/home/pistacchio/lib/perl5:/home/pistacchio/lib/perl5/lib:/home/pistacchio/lib/perl5/lib/i386-linux-thread-multi [..] Removing use Template gets rid of the problem. Can anybody help?

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  • How do I set Perl's @INC for a CGI script?

    - by pistacchio
    I have the follwing, simplest Perl CGI script: use strict; use warnings; use CGI(); use CGI::Carp qw(fatalsToBrowser); use Template; print CGI::header(); foreach(@INC) { print "$_\n"; } When called (http://[..]/cgi-bin/p.cgi) I am given the following error: Can't locate Template.pm in @INC (@INC contains: /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi /usr/lib/perl5/site_perl/5.8.8 /usr/lib/perl5/site_perl /usr/lib/perl5/vendor_perl/5.8.8/i386-linux-thread-multi /usr/lib/perl5/vendor_perl/5.8.8 /usr/lib/perl5/vendor_perl /usr/lib/perl5/5.8.8/i386-linux-thread-multi /usr/lib/perl5/5.8.8 .) at /home/pistacchio/webapps/htdocs/cgi-bin/p.cgi line 8. BEGIN failed--compilation aborted at /home/pistacchio/webapps/htdocs/cgi-bin/p.cgi line 8. I made sure that Template is installed and indeed when running this program from shell it works (loads Template) and outputs: Content-Type: text/html; charset=ISO-8859-1 /home/pistacchio/lib/perl5 /home/pistacchio/lib/perl5/lib/i386-linux-thread-multi /home/pistacchio/lib/perl5/lib /home/pistacchio/lib/perl5/lib/i386-linux-thread-multi /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi /usr/lib/perl5/site_perl/5.8.8 /usr/lib/perl5/site_perl /usr/lib/perl5/vendor_perl/5.8.8/i386-linux-thread-multi /usr/lib/perl5/vendor_perl/5.8.8 /usr/lib/perl5/vendor_perl /usr/lib/perl5/5.8.8/i386-linux-thread-multi /usr/lib/perl5/5.8.8 Template is installed in /home/pistacchio/lib/perl5/lib/i386-linux-thread-multi [pistacchio@web118 i386-linux-thread-multi]$ pwd /home/pistacchio/lib/perl5/lib/i386-linux-thread-multi [pistacchio@web118 i386-linux-thread-multi]$ ls auto perllocal.pod Template Template.pm This directory is correctly listed in env and, as previously posted, in @INC. In @INC it is shown twice, so I even tried to pop it out before calling use Template, but without result. From env: [pistacchio@web118 i386-linux-thread-multi]$ env [..] PERL5LIB=/home/pistacchio/lib/perl5:/home/pistacchio/lib/perl5/lib:/home/pistacchio/lib/perl5/lib/i386-linux-thread-multi [..] Removing use Template gets rid of the problem.

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  • How to parallelize this groovy code?

    - by lucas
    I'm trying to write a reusable component in Groovy to easily shoot off emails from some of our Java applications. I would like to pass it a List, where Email is just a POJO(POGO?) with some email info. I'd like it to be multithreaded, at least running all the email logic in a second thread, or make one thread per email. I am really foggy on multithreading in Java so that probably doesn't help! I've attempted a few different ways, but here is what I have right now: void sendEmails(List<Email> emails) { def threads = [] def sendEm = emails.each{ email -> def th = new Thread({ Random rand = new Random() def wait = (long)(rand.nextDouble() * 1000) println "in closure" this.sleep wait sendEmail(email) }) println "putting thread in list" threads << th } threads.each { it.run() } threads.each { it.join() } } I was hoping the sleep would randomly slow some threads down so the console output wouldn't be sequential. Instead, I see this: putting thread in list putting thread in list putting thread in list putting thread in list putting thread in list putting thread in list putting thread in list putting thread in list putting thread in list putting thread in list in closure sending email1 in closure sending email2 in closure sending email3 in closure sending email4 in closure sending email5 in closure sending email6 in closure sending email7 in closure sending email8 in closure sending email9 in closure sending email10 sendEmail basically does what you'd expect, including the println statement, and the client that calls this follows, void doSomething() { Mailman emailer = MailmanFactory.getExchangeEmailer() def to = ["one","two"] def from = "noreply" def li = [] def email (1..10).each { email = new Email(to,null,from,"email"+it,"hello") li << email } emailer.sendEmails li }

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