multithreading - Many threads are blocked and memory from old gen not releasing -


i using tomcat server , when took thread dump can see many threads blocked (172) , other threads in_native (27). many blocked threads smiler below. can 1 may reason. 8gb oldgen space full. after performing gc not releasing.

blocked threads :

    thread 22614 - threadid:thread 22614 - state:blocked stacktrace: - java.net.socketinputstream.socketread0(java.io.filedescriptor, byte[], int, int, int) @bci=0 (compiled frame; information may imprecise) - java.net.socketinputstream.read(byte[], int, int, int) @bci=87, line=152 (compiled frame) - java.net.socketinputstream.read(byte[], int, int) @bci=11, line=122 (compiled frame) - org.apache.coyote.http11.internalinputbuffer.fill(boolean) @bci=59, line=512 (compiled frame) - org.apache.coyote.http11.internalinputbuffer.fill() @bci=2, line=497 (compiled frame) - org.apache.coyote.http11.http11processor.process(org.apache.tomcat.util.net.socketwrapper) @bci=263, line=203 (compiled frame) - org.apache.coyote.abstractprotocol$abstractconnectionhandler.process(org.apache.tomcat.util.net.socketwrapper, org.apache.tomcat.util.net.socketstatus) @bci=96, line=515 (compiled frame) - org.apache.tomcat.util.net.jioendpoint$socketprocessor.run() @bci=130, line=302 (compiled frame) - java.util.concurrent.threadpoolexecutor.runworker(java.util.concurrent.threadpoolexecutor$worker) @bci=95, line=1145 (compiled frame) - java.util.concurrent.threadpoolexecutor$worker.run() @bci=5, line=615 (interpreted frame) - java.lang.thread.run() @bci=11, line=745 (interpreted frame)     thread 23677 - threadid:thread 23677 - state:blocked stacktrace: - sun.misc.unsafe.park(boolean, long) @bci=0 (compiled frame; information may imprecise) - java.util.concurrent.locks.locksupport.parknanos(java.lang.object, long) @bci=20, line=226 (compiled frame) - java.util.concurrent.locks.abstractqueuedsynchronizer$conditionobject.awaitnanos(long) @bci=68, line=2082 (compiled frame) - java.util.concurrent.linkedblockingqueue.poll(long, java.util.concurrent.timeunit) @bci=62, line=467 (compiled frame) - org.apache.tomcat.util.threads.taskqueue.poll(long, java.util.concurrent.timeunit) @bci=3, line=86 (compiled frame) - org.apache.tomcat.util.threads.taskqueue.poll(long, java.util.concurrent.timeunit) @bci=3, line=32 (compiled frame) - java.util.concurrent.threadpoolexecutor.gettask() @bci=141, line=1068 (compiled frame) - java.util.concurrent.threadpoolexecutor.runworker(java.util.concurrent.threadpoolexecutor$worker) @bci=26, line=1130 (compiled frame) - java.util.concurrent.threadpoolexecutor$worker.run() @bci=5, line=615 (interpreted frame) - java.lang.thread.run() @bci=11, line=745 (interpreted frame)   thread 23674 - threadid:thread 23674 - state:blocked stacktrace: - com.mysql.jdbc.singlebytecharsetconverter.tostring(byte[], int, int) @bci=1, line=322 (compiled frame) - com.mysql.jdbc.resultsetrow.getstring(java.lang.string, com.mysql.jdbc.mysqlconnection, byte[], int, int) @bci=54, line=797 (compiled frame) - com.mysql.jdbc.bytearrayrow.getstring(int, java.lang.string, com.mysql.jdbc.mysqlconnection) @bci=24, line=72 (compiled frame) - com.mysql.jdbc.resultsetimpl.getstringinternal(int, boolean) @bci=155, line=5699 (compiled frame) - com.mysql.jdbc.resultsetimpl.getstring(int) @bci=3, line=5576 (compiled frame) - com.mysql.jdbc.resultsetimpl.getstring(java.lang.string) @bci=6, line=5616 (compiled frame) - com.mchange.v2.c3p0.impl.newproxyresultset.getstring(java.lang.string) @bci=19, line=3342 (compiled frame) - org.hibernate.type.stringtype.get(java.sql.resultset, java.lang.string) @bci=2, line=41 (compiled frame) - org.hibernate.type.nullabletype.nullsafeget(java.sql.resultset, java.lang.string) @bci=3, line=184 (compiled frame) - org.hibernate.type.nullabletype.nullsafeget(java.sql.resultset, java.lang.string, org.hibernate.engine.sessionimplementor, java.lang.object) @bci=3, line=210 (compiled frame)

  • first stack trace indicates thread tried read socket , went blocked state. socket read operation blocking operation means if there nothing read or till information read, block.

  • for second, linkedblockingqueue.poll() not blocking operation normal stack trace indicate usual idle thread. not caused user code

  • for third, doesn't problematic string value result set returned.

i think, should @ this too.

stack trace # 1 , #3 might related socket read might db read.

these stack traces not solve problem these kind of blocked threads indicate problem memory , excessive garbage collection.

there might problem c3p0 pool or way might creating statement , result set objects - in seems case of memory leak , resources not closing well.

very precise answer not possible without relevant application code. also, stated in comment, identity of lock object needs dumped too.

hope helps !!


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