jvm

问题 I have machine with 16G RAM. I run a java application with arguments -Xms9G -Xmx9G . When I run top command I see that my java process is taking 13.8g VIRT , but only 4.6g of RES . PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 5019 root 20 0 13.8g 4.7g 18m S 0.7 30.7 3:28.39 java On running pmap command, I see that only ~3.9g of heap is present as RES , rest 5.7g is in virtual . Address Kbytes RSS Dirty Mode Mapping 0000000580000000 9452384 4074228 4074228 rw--- [ anon ] Upon

问题 This question already has answers here : Java Thread Garbage collected or not (4 answers) Closed 5 years ago . From the Java API doc: The Java Virtual Machine continues to execute threads until following occurs: All threads that are not daemon threads have died, either by returning from the call to the run method or by throwing an exception that propagates beyond the run method. I hope my assumption is correct that once thread finishes its run() method it becomes eligible for garbage

问题 I cannot load a class after byte code modification with ASM library. Here it is identity transformer and I expect to get modified array with the same size as bytes one, but it 2 times shorter! (439 vs 278) String path = SimpleClass.class.getName().replace(".", "/") + ".class"; ClassLoader classLoader = SimpleClass.class.getClassLoader(); InputStream is = classLoader.getResourceAsStream(path); byte[] bytes = IOUtils.toByteArray(is); ClassReader reader = new ClassReader(bytes); ClassWriter

问题 In a project I'm working on, the application is launched using a command similar to this: java -Djava.security.egd=file:/dev/urandom -jar app.jar I've never seen the java.security.egd option before. Searching a bit, it seems to be used to configure random number generation in a Java application. Is it right? When is it supposed to be applied? 回答1: Java applications can and should use java.security.SecureRandom class to produce cryptographically strong random values by using a

问题 In a project I'm working on, the application is launched using a command similar to this: java -Djava.security.egd=file:/dev/urandom -jar app.jar I've never seen the java.security.egd option before. Searching a bit, it seems to be used to configure random number generation in a Java application. Is it right? When is it supposed to be applied? 回答1: Java applications can and should use java.security.SecureRandom class to produce cryptographically strong random values by using a

问题 In Spark's WebUI (port 8080) and on the environment tab there is a setting of the below: user.timezone Zulu Do you know how/where I can override this to UTC? Env details: Spark 2.1.1 jre-1.8.0-openjdk.x86_64 no jdk EC2 Amazon Linux EDIT (someone answered the below then deleted): https://www.timeanddate.com/time/zones/z 回答1: Change your system timezone and check it I hope it will works 回答2: Now you can use: spark.conf.set("spark.sql.session.timeZone", "UTC") Since https://issues.apache.org

问题 How can I suspend the execution of a JVM for a configurable amount of time, similar to want happens on a full, serial, Garbage Collection? I want to test some edge cases but it's difficult to create the exact pauses I need with manually generating garbage + System.gc() . I'm trying to 'freeze' all the threads in the application, to simulate a situation where an application becomes unresponsive, and then resumes execution. The application is part of a cluster, and I'm trying to debug some

问题 How can I suspend the execution of a JVM for a configurable amount of time, similar to want happens on a full, serial, Garbage Collection? I want to test some edge cases but it's difficult to create the exact pauses I need with manually generating garbage + System.gc() . I'm trying to 'freeze' all the threads in the application, to simulate a situation where an application becomes unresponsive, and then resumes execution. The application is part of a cluster, and I'm trying to debug some

问题 I just read some blogs about G1 algorithm. The usage of remembered-set is confused to me. Here is what I think: Since we can use DFS to walk through every reference from GC-Roots, why do we need remembered-set? Cause all the blogs to say the reason why we use remembered-set is we don't need to check every region to see if there is an object that is referenced by GC-Roots 回答1: You need to understand what Card Table is first, IMO. How do you scan only young generation region and clean it, if

问题 Running a maven build using java 11, the build issues the following warning whilerunning tests: [WARNING] Corrupted STDOUT by directly writing to native stream in forked JVM 1. See FAQ web page and the dump file /home/thomas/code/irdeto-control/fps-license-service/fps/target/surefire-reports/2019-04-11T14-05-32_318-jvmRun1.dumpstream ...followed by the following stderr output after the build fails: $ cat error.message [ERROR] Failed to execute goal org.apache.maven.plugins:maven-surefire