Hello,

When somebody is downloading something from hudson (1.57) it synchronizes. So
only one item (artifact) can be downloaded at a time. But is also lock other
requests like 'schedule a build' requests.
I have a stacktrace from Tomcat (5.5.17) for you. If you need more info. You can
contact me.

"http-8080-Processor22" daemon prio=1 tid=0x893af0a0 nid=0x897 waiting for
monitor entry [0x8a46b000..0x8a46d740]
at hudson.model.Actionable.getActions(Actionable.java:27)

• waiting to lock <0xab127e90> (a hudson.model.Build)
  at hudson.model.Actionable.getAction(Actionable.java:38)
  at hudson.model.Build.getTestResultAction(Build.java:126)
  at sun.reflect.GeneratedMethodAccessor131.invoke(Unknown Source)
  at
  sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
  at java.lang.reflect.Method.invoke(Method.java:585)
  at
  org.apache.commons.jexl.util.PropertyExecutor.execute(PropertyExecutor.java:123)
  at
  org.apache.commons.jexl.util.introspection.UberspectImpl$VelGetterImpl.invoke(UberspectImpl.java:287)
  at
  org.apache.commons.jexl.parser.ASTArrayAccess.evaluateExpr(ASTArrayAccess.java:183)
  at org.apache.commons.jexl.parser.ASTIdentifier.execute(ASTIdentifier.java:73)
  at org.apache.commons.jexl.parser.ASTReference.execute(ASTReference.java:82)
  at org.apache.commons.jexl.parser.ASTReference.value(ASTReference.java:56)
  at
  org.apache.commons.jexl.parser.ASTReferenceExpression.value(ASTReferenceExpression.java:50)
  at org.apache.commons.jexl.ExpressionImpl.evaluate(ExpressionImpl.java:79)
  at
  org.apache.commons.jelly.expression.jexl.JexlExpression.evaluate(JexlExpression.java:69)
  at
  org.apache.commons.jelly.expression.jexl.JexlExpressionFactory$ExpressionSupportLocal.evaluate(JexlExpressionFactory.java:122)
  at org.apache.commons.jelly.tags.core.SetTag.doTag(SetTag.java:84)
  at org.apache.commons.jelly.impl.TagScript.run(TagScript.java:262)
  at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
  at org.apache.commons.jelly.TagSupport.invokeBody(TagSupport.java:186)
  at org.apache.commons.jelly.impl.StaticTag.doTag(StaticTag.java:65)
  at org.apache.commons.jelly.impl.StaticTagScript.run(StaticTagScript.java:112)
  at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
  at org.apache.commons.jelly.TagSupport.invokeBody(TagSupport.java:186)
  at org.apache.commons.jelly.tags.core.JellyTag.doTag(JellyTag.java:45)
  at org.apache.commons.jelly.impl.TagScript.run(TagScript.java:262)
  at org.kohsuke.stapler.jelly.IncludeTag.doTag(IncludeTag.java:73)
  at org.apache.commons.jelly.impl.TagScript.run(TagScript.java:262)
  at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
  at
  org.apache.commons.jelly.tags.define.InvokeBodyTag.doTag(InvokeBodyTag.java:91)

"http-8080-Processor14" daemon prio=1 tid=0x08375c98 nid=0x2875 runnable
[0x8907e000..0x8907f840]
at java.net.SocketOutputStream.socketWrite0(Native Method)
at java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:92)
at java.net.SocketOutputStream.write(SocketOutputStream.java:136)
at
org.apache.coyote.http11.InternalOutputBuffer.realWriteBytes(InternalOutputBuffer.java:746)
at org.apache.tomcat.util.buf.ByteChunk.flushBuffer(ByteChunk.java:433)
at org.apache.tomcat.util.buf.ByteChunk.append(ByteChunk.java:348)
at
org.apache.coyote.http11.InternalOutputBuffer$OutputStreamOutputBuffer.doWrite(InternalOutputBuffer.java:769)
at
org.apache.coyote.http11.filters.IdentityOutputFilter.doWrite(IdentityOutputFilter.java:117)
at
org.apache.coyote.http11.InternalOutputBuffer.doWrite(InternalOutputBuffer.java:579)
at org.apache.coyote.Response.doWrite(Response.java:559)
at
org.apache.catalina.connector.OutputBuffer.realWriteBytes(OutputBuffer.java:361)
at org.apache.tomcat.util.buf.ByteChunk.flushBuffer(ByteChunk.java:433)
at org.apache.tomcat.util.buf.ByteChunk.append(ByteChunk.java:348)
at org.apache.catalina.connector.OutputBuffer.writeBytes(OutputBuffer.java:392)
at org.apache.catalina.connector.OutputBuffer.write(OutputBuffer.java:381)
at
org.apache.catalina.connector.CoyoteOutputStream.write(CoyoteOutputStream.java:88)
at org.kohsuke.stapler.Stapler.serveStaticResource(Stapler.java:140)
at org.kohsuke.stapler.ResponseImpl.serveFile(ResponseImpl.java:41)
at hudson.model.DirectoryHolder.serveFile(DirectoryHolder.java:102)
at hudson.model.Run.doArtifact(Run.java:608)

• locked <0xab99a1f0> (a hudson.model.Build)
  at sun.reflect.GeneratedMethodAccessor159.invoke(Unknown Source)
  at
  sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
  at java.lang.reflect.Method.invoke(Method.java:585)
  at org.kohsuke.stapler.Function$InstanceFunction.invoke(Function.java:50)
  at org.kohsuke.stapler.MetaClass$6.doDispatch(MetaClass.java:122)
  at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:30)
  at org.kohsuke.stapler.Stapler.invoke(Stapler.java:212)
  at org.kohsuke.stapler.MetaClass$2.doDispatch(MetaClass.java:75)
  at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:30)
  at org.kohsuke.stapler.Stapler.invoke(Stapler.java:212)

"http-8080-Processor3" daemon prio=1 tid=0x089e5608 nid=0x271d waiting for
monitor entry [0x8a6eb000..0x8a6ed640]
at hudson.model.Actionable.getActions(Actionable.java:27)

• waiting to lock <0xab127e90> (a hudson.model.Build)
  at hudson.model.Actionable.getAction(Actionable.java:38)
  at hudson.model.Build.getTestResultAction(Build.java:126)
  at sun.reflect.GeneratedMethodAccessor131.invoke(Unknown Source)
  at
  sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
  at java.lang.reflect.Method.invoke(Method.java:585)
  at
  org.apache.commons.jexl.util.PropertyExecutor.execute(PropertyExecutor.java:123)
  at
  org.apache.commons.jexl.util.introspection.UberspectImpl$VelGetterImpl.invoke(UberspectImpl.java:287)
  at
  org.apache.commons.jexl.parser.ASTArrayAccess.evaluateExpr(ASTArrayAccess.java:183)
  at org.apache.commons.jexl.parser.ASTIdentifier.execute(ASTIdentifier.java:73)
  at org.apache.commons.jexl.parser.ASTReference.execute(ASTReference.java:82)
  at org.apache.commons.jexl.parser.ASTReference.value(ASTReference.java:56)
  at
  org.apache.commons.jexl.parser.ASTReferenceExpression.value(ASTReferenceExpression.java:50)
  at org.apache.commons.jexl.ExpressionImpl.evaluate(ExpressionImpl.java:79)
  at
  org.apache.commons.jelly.expression.jexl.JexlExpression.evaluate(JexlExpression.java:69)
  at
  org.apache.commons.jelly.expression.jexl.JexlExpressionFactory$ExpressionSupportLocal.evaluate(JexlExpressionFactory.java:122)
  at org.apache.commons.jelly.tags.core.SetTag.doTag(SetTag.java:84)
  at org.apache.commons.jelly.impl.TagScript.run(TagScript.java:262)
  at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
  at org.apache.commons.jelly.TagSupport.invokeBody(TagSupport.java:186)
  at org.apache.commons.jelly.impl.StaticTag.doTag(StaticTag.java:65)
  at org.apache.commons.jelly.impl.StaticTagScript.run(StaticTagScript.java:112)
  at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
  at org.apache.commons.jelly.TagSupport.invokeBody(TagSupport.java:186)
  at org.apache.commons.jelly.tags.core.JellyTag.doTag(JellyTag.java:45)
  at org.apache.commons.jelly.impl.TagScript.run(TagScript.java:262)
  at org.kohsuke.stapler.jelly.IncludeTag.doTag(IncludeTag.java:73)
  at org.apache.commons.jelly.impl.TagScript.run(TagScript.java:262)
  at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
  at
  org.apache.commons.jelly.tags.define.InvokeBodyTag.doTag(InvokeBodyTag.java:91)
  at org.apache.commons.jelly.impl.TagScript.run(TagScript.java:262)
  at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
  at org.apache.commons.jelly.TagSupport.invokeBody(TagSupport.java:186)
  at org.apache.commons.jelly.tags.core.IfTag.doTag(IfTag.java:42)
  at org.apache.commons.jelly.impl.TagScript.run(TagScript.java:262)
  at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
  at org.apache.commons.jelly.TagSupport.invokeBody(TagSupport.java:186)
  at org.apache.commons.jelly.tags.core.JellyTag.doTag(JellyTag.java:45)