jvms | JDK Version Manager for Windows | Runtime Evironment library
kandi X-RAY | jvms Summary
kandi X-RAY | jvms Summary
Manage multiple installations of JDK on a Windows computer. JVMS, Download Now!. There are situations where the ability to switch between different versions of JDK can be very useful. For example, if you want to test a project you're developing with the latest bleeding edge version without uninstalling the stable version of JDK, this utility can help.
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Trending Discussions on jvms
QUESTION
Android studio is not launching my device with the app, instead just the device alone. After the app is built with gradle it spins saying "waiting for device to come online".
Things I've tried:
- In developer settings revoking permissions, turning on usb debugging, connecting and disconnecting a physical device
- Wiping data and cold booting emulators
- Different emulators on api 29 and 30, Pixel 3, 3a, 4
- Changing from Media Device (MTP) to Camera (PTP)
- Restarting my computer, Android Studio, Invalidating caches
- Different JDKs, JVMs
- Reinstalling Android Studio
- Adjusting the permissions of Android studio using
sudo chown -R $USER - Restarting the abd server
Any suggestions would be great, here is a screen shot of the error as described for reference:
...ANSWER
Answered 2022-Apr-10 at 20:01Reading many questions along these lines I found a suggestion to run adb devices. Doing that revealed emulator-5554 unauthorized, and googling that showed a stack overflow question with the solution:
emulator-5554 unauthorized for adb devices
The solution: create a new device of any hardware type but don't use the recommended system images. Instead go to the x86 Images tab and select one with (Google Apis) instead of (Google Play).
No more restarting or cold booting or wiping after that, simply building the app resulted in it now launching!
QUESTION
I am writing a JVM.
I was implementing all opcodes one by one, until I faced dup2.
The oracle instruction set https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-6.html#jvms-6.5.dup2 says
Duplicate the top one or two values on the operand stack and push the duplicated value or values back onto the operand stack in the original order
How am I supposed to choose which operation to perform? How can I know when I should duplicate only the top or I should duplicate the top two values?
...ANSWER
Answered 2022-Feb-26 at 14:35The description of the opcode says:
Form 1:
..., value2, value1 →
..., value2, value1, value2, value1
where both value1 and value2 are values of a category 1 computational type (§2.11.1).
Form 2:
..., value →
..., value, value
where value is a value of a category 2 computational type (§2.11.1).
Category 2 types are long and double, and category 1 are others. So in the original versions of Java Category 2 types meant 64 bit type and Category 1 meant 32 bit types. When 64 bit JVMs were introduced, that distinction no longer worked. Now an interpreter or JIT compiler needs to track the categories of values pushed and popped from the opstack to the extent that it knows whether the value on the top of stack is category 1 or 2.
Note that the JVM needs to this kind of analysis at verify time in order to check the requirements set out in 4.10.1.7. Type Checking Load and Store Instructions
QUESTION
I need to convert a UUID (like ffffffff-ffff-ffff-ffff-ffffffffffff) to a number with as least digits as possible. These UUIDs are being generated by com.fasterxml.uuid.impl.TimeBasedGenerator.java.
ANSWER
Answered 2022-Feb-17 at 17:13QUESTION
Infinispan supports a type of cache tier called "Replicated" where the content of multiple caches (in different JVMs or even container instances/VMs/servers) are kept (asynchronously) synchronized. My question is how eviction is handled in this case - if a normal local eviction algorithm is used that only looks at one cache it sounds to me like the result would be suboptimal i.e. entries that is not used much in one JVM and therefore are evicted could be the most frequently used one in all the others (that, as I understand it, also will see these entries evicted due to the synchronization between them)...
...ANSWER
Answered 2022-Feb-07 at 14:02You will want to check out this section of the Infinispan User Guide https://infinispan.org/docs/stable/titles/configuring/configuring.html#eviction-and-expiration_configuring-memory-usage
As you mentioned eviction is done per node and removes entries that were deemed to be used the least most recently. (Note that off JVM heap and on heap have slightly different algorithms). Due to this it is possible to have some nodes with and without data if you have run out of entries. This in turn can cause inconsistencies with what each node can see.
If you need to limit memory usage, which is the main point of eviction, all you need to do to keep consistency between all nodes is to have a persistent storage defined, such as file store which is covered in the next section https://infinispan.org/docs/stable/titles/configuring/configuring.html#persistence.
Note that expiration differs from eviction in that it is done cluster wide. So if you still want data consistency across all nodes, expiration can be used instead if it is sufficient for your use case.
QUESTION
I have a question regarding converting and loading in java. If you use e.g. long='A'. The Java Virtual Machine Specification at https://docs.oracle.com/javase/specs/jvms/se16/html/jvms-6.html specifies this as a conversion. Here the char is converted to a long.
If, however, a value is in a variable or an array, then Java does not speak any more of converting, but of loading. Here it says that then the array value is loaded and not converted. What I also knew before that if one acts with a variable of another data type that this variable is not converted, but by intermediate steps its information is taken and the information of it is converted, but not the variable. What exactly is the difference between converting and loading as Java describes here: https://docs.oracle.com/javase/specs/jvms/se16/html/jvms-6.html?
JVMS usage of convert
JVMS usage of load
...ANSWER
Answered 2021-Dec-18 at 06:06A conversion changes a value from one type to another.
As the documentation for the d2f instruction says, a double value on the top of the stack is converted to a float and pushed back onto the stack as a float.
Loading is moving a value of the same type from one place to another, without any changes to the value.
You are talking about JVM instructions, which is what Java is compiled into.
Java performs conversions as needed, for instance:
QUESTION
According to the jvms11, there are two kinds of entry in the run-time constant pool: symbolic references, which may later be resolved, and static constants, which require no further processing. The static constants in the run-time constant pool are also derived from entries in the constant_pool table in accordance with the structure of each entry.
My understanding is String.intern has nothing to to with JVM Run-Time Constant pool, but someone who is one of the greatest programmer in China said String.intern would "put something in the Run-Time Constant pool during runtime" in his popular book. We argued about this for a long time，we both can't convince each other.
So my question is, does String.intern has anything to to with JVM Run-Time Constant pool?
Here is the jvms5.1 about Rum-Time Constant pool
...ANSWER
Answered 2021-Dec-14 at 13:18The JVMS §5.1 says
The Java Virtual Machine maintains a run-time constant pool for each class and interface (§2.5.5).
The term “for each” means that there is not one run-time constant pool, but each class or interface has its own dedicated pool. The subsequent sentences make even clear that this data structure corresponds to the constant pool of a class file.
The
constant_pooltable in the binary representation of a class or interface (§4.4) is used to construct the run-time constant pool upon class or interface creation (§5.3).
It should be clear that this per-class structure is not the same as the single global data structure used to canonicalize string instances throughout the entire runtime.
But since all uses of string constants in a class file are expressed as indices into the class file’s constant pool which is then used to construct the class’s run-time constant pool, there is a relationship between these uses and the global data structure. As stated within §5.1
The static constants in the run-time constant pool are also derived from entries in the
constant_pooltable in accordance with the structure of each entry:
- A string constant is a
referenceto an instance of classString, and is derived from aCONSTANT_String_infostructure (§4.4.3). To derive a string constant, the Java Virtual Machine examines the sequence of code points given by theCONSTANT_String_infostructure:
- If the method
String.internhas previously been invoked on an instance of classStringcontaining a sequence of Unicode code points identical to that given by theCONSTANT_String_infostructure, then the string constant is areferenceto that same instance of classString.- Otherwise, a new instance of class
Stringis created containing the sequence of Unicode code points given by theCONSTANT_String_infostructure. The string constant is areferenceto the new instance. Finally, the methodString.internis invoked on the new instance.
So formally, the String instances corresponding to the string constants used in a class are part of that class’s runtime constant pool but initialized in terms of String.intern to ensure that each class has canonicalized string instances in its pool.
But this relationship has only one direction. When application code invokes String.intern() explicitly, it won’t access a class’s run-time constant pool. It wouldn’t even be clear, which run-time constant pool we shall expect to be accessed.
So intern() has nothing do to with the run-time constant pool, at least not more than it has to do with every other caller.
A source of confusion is the fact that the data structure used by the JVM to implement intern() has no name in the JVMS or JLS at all. So, without a formal name, different names appear in different media. E.g., the API documentation of intern() says
A pool of strings, initially empty, is maintained privately by the class
String.
It’s typically some kind of hash table, but the term “pool” matches its purpose and since it exists at runtime, it’s not surprising that people come up with terms easy to confuse with the run-time constant pools of JVMS §5.1.
So before starting a heated discussion with another developer, it’s important to clarify, whether everyone is talking about the same pool.
As an addendum, I said above that the String is formally part of the run-time constant pool, as this hits implementation specific aspects.
In principle, a JVM could initialize all string entries of a class’s run-time constant pool with String instances when creating the pool. But as this answer demonstrates, this is not the case for the widely used HotSpot JVM which looks up or creates a String instance on the first use rather than class initialization time.
This implies that the run-time constant pool contains the raw character data in some form instead of a reference to a String instance. Once the String is constructed, it is referenced and reused by the code, but whether the run-time constant pool is modified to reference the String now or the bytecode instruction (ldc) keeps it, is not observable from the Java application. All we can observe, is that the String instance does not get garbage collected as long as the class exist.
QUESTION
I am using elasticsearch 5.6.13 version, I need some experts configurations for the elasticsearch. I have 3 nodes in the same system (node1,node2,node3) where node1 is master and else 2 data nodes. I have number of indexes around 40, I created all these indexes with default 5 primary shards and some of them have 2 replicas. What I am facing the issue right now, My data (scraping) is growing day by day and I have 400GB of the data in my one of index. similarly 3 other indexes are also very loaded. From some last days I am facing the issue while insertion of data my elasticsearch hangs and then the service is killed which effect my processing. I have tried several things. I am sharing the system specs and current ES configuration + logs. Please suggest some solution.
The System Specs: RAM: 160 GB, CPU: AMD EPYC 7702P 64-Core Processor, Drive: 2 TB SSD (The drive in which the ES installed still have 500 GB left)
ES Configuration JVM options: -Xms26g, -Xmx26g (I just try this but not sure what is the perfect heap size for my scenario) I just edit this above lines and the rest of the file is as defult. I edit this on all three nodes jvm.options files.
ES LOGS
[2021-09-22T12:05:17,983][WARN ][o.e.m.j.JvmGcMonitorService] [sashanode1] [gc][170] overhead, spent [7.1s] collecting in the last [7.2s] [2021-09-22T12:05:21,868][WARN ][o.e.m.j.JvmGcMonitorService] [sashanode1] [gc][171] overhead, spent [3.7s] collecting in the last [1.9s] [2021-09-22T12:05:51,190][WARN ][o.e.m.j.JvmGcMonitorService] [sashanode1] [gc][172] overhead, spent [27.7s] collecting in the last [23.3s] [2021-09-22T12:06:54,629][WARN ][o.e.m.j.JvmGcMonitorService] [cluster_name] [gc][173] overhead, spent [57.5s] collecting in the last [1.1m] [2021-09-22T12:06:56,536][WARN ][o.e.m.j.JvmGcMonitorService] [cluster_name] [gc][174] overhead, spent [1.9s] collecting in the last [1.9s] [2021-09-22T12:07:02,176][WARN ][o.e.m.j.JvmGcMonitorService] [cluster_name] [gc][175] overhead, spent [5.4s] collecting in the last [5.6s] [2021-09-22T12:06:56,546][ERROR][o.e.i.e.Engine ] [cluster_name] [index_name][3] merge failed java.lang.OutOfMemoryError: Java heap space
[2021-09-22T12:06:56,548][ERROR][o.e.b.ElasticsearchUncaughtExceptionHandler] [cluster_name] fatal error in thread [elasticsearch[cluster_name][bulk][T#25]], exiting java.lang.OutOfMemoryError: Java heap space
Some more logs
[2021-09-22T12:10:06,526][INFO ][o.e.n.Node ] [cluster_name] initializing ... [2021-09-22T12:10:06,589][INFO ][o.e.e.NodeEnvironment ] [cluster_name] using [1] data paths, mounts [[(D:)]], net usable_space [563.3gb], net total_space [1.7tb], spins? [unknown], types [NTFS] [2021-09-22T12:10:06,589][INFO ][o.e.e.NodeEnvironment ] [cluster_name] heap size [1.9gb], compressed ordinary object pointers [true] [2021-09-22T12:10:07,239][INFO ][o.e.n.Node ] [cluster_name] node name [sashanode1], node ID [2p-ux-OXRKGuxmN0efvF9Q] [2021-09-22T12:10:07,240][INFO ][o.e.n.Node ] [cluster_name] version[5.6.13], pid[57096], build[4d5320b/2018-10-30T19:05:08.237Z], OS[Windows Server 2019/10.0/amd64], JVM[Oracle Corporation/Java HotSpot(TM) 64-Bit Server VM/1.8.0_261/25.261-b12] [2021-09-22T12:10:07,240][INFO ][o.e.n.Node ] [cluster_name] JVM arguments [-Xms2g, -Xmx2g, -XX:+UseConcMarkSweepGC, -XX:CMSInitiatingOccupancyFraction=75, -XX:+UseCMSInitiatingOccupancyOnly, -XX:+AlwaysPreTouch, -Xss1m, -Djava.awt.headless=true, -Dfile.encoding=UTF-8, -Djna.nosys=true, -Djdk.io.permissionsUseCanonicalPath=true, -Dio.netty.noUnsafe=true, -Dio.netty.noKeySetOptimization=true, -Dio.netty.recycler.maxCapacityPerThread=0, -Dlog4j.shutdownHookEnabled=false, -Dlog4j2.disable.jmx=true, -Dlog4j.skipJansi=true, -XX:+HeapDumpOnOutOfMemoryError, -Delasticsearch, -Des.path.home=D:\Databases\ES\elastic and kibana 5.6.13\es_node_1, -Des.default.path.logs=D:\Databases\ES\elastic and kibana 5.6.13\es_node_1\logs, -Des.default.path.data=D:\Databases\ES\elastic and kibana 5.6.13\es_node_1\data, -Des.default.path.conf=D:\Databases\ES\elastic and kibana 5.6.13\es_node_1\config, exit, -Xms2048m, -Xmx2048m, -Xss1024k]
Also in my ES folder there are so many files with the random names (java_pid197036.hprof) Further details can be shared please suggest any further configurations. Thanks
The output for _cluster/stats?pretty&human is
{ "_nodes": { "total": 3, "successful": 3, "failed": 0 }, "cluster_name": "cluster_name", "timestamp": 1632375228033, "status": "red", "indices": { "count": 42, "shards": { "total": 508, "primaries": 217, "replication": 1.3410138248847927, "index": { "shards": { "min": 2, "max": 60, "avg": 12.095238095238095 }, "primaries": { "min": 1, "max": 20, "avg": 5.166666666666667 }, "replication": { "min": 1.0, "max": 2.0, "avg": 1.2857142857142858 } } }, "docs": { "count": 107283077, "deleted": 1047418 }, "store": { "size": "530.2gb", "size_in_bytes": 569385384976, "throttle_time": "0s", "throttle_time_in_millis": 0 }, "fielddata": { "memory_size": "0b", "memory_size_in_bytes": 0, "evictions": 0 }, "query_cache": { "memory_size": "0b", "memory_size_in_bytes": 0, "total_count": 0, "hit_count": 0, "miss_count": 0, "cache_size": 0, "cache_count": 0, "evictions": 0 }, "completion": { "size": "0b", "size_in_bytes": 0 }, "segments": { "count": 3781, "memory": "2gb", "memory_in_bytes": 2174286255, "terms_memory": "1.7gb", "terms_memory_in_bytes": 1863786029, "stored_fields_memory": "105.6mb", "stored_fields_memory_in_bytes": 110789048, "term_vectors_memory": "0b", "term_vectors_memory_in_bytes": 0, "norms_memory": "31.9mb", "norms_memory_in_bytes": 33527808, "points_memory": "13.1mb", "points_memory_in_bytes": 13742470, "doc_values_memory": "145.3mb", "doc_values_memory_in_bytes": 152440900, "index_writer_memory": "0b", "index_writer_memory_in_bytes": 0, "version_map_memory": "0b", "version_map_memory_in_bytes": 0, "fixed_bit_set": "0b", "fixed_bit_set_memory_in_bytes": 0, "max_unsafe_auto_id_timestamp": 1632340789677, "file_sizes": { } } }, "nodes": { "count": { "total": 3, "data": 3, "coordinating_only": 0, "master": 1, "ingest": 3 }, "versions": [ "5.6.13" ], "os": { "available_processors": 192, "allocated_processors": 96, "names": [ { "name": "Windows Server 2019", "count": 3 } ], "mem": { "total": "478.4gb", "total_in_bytes": 513717497856, "free": "119.7gb", "free_in_bytes": 128535437312, "used": "358.7gb", "used_in_bytes": 385182060544, "free_percent": 25, "used_percent": 75 } }, "process": { "cpu": { "percent": 5 }, "open_file_descriptors": { "min": -1, "max": -1, "avg": 0 } }, "jvm": { "max_uptime": "1.9d", "max_uptime_in_millis": 167165106, "versions": [ { "version": "1.8.0_261", "vm_name": "Java HotSpot(TM) 64-Bit Server VM", "vm_version": "25.261-b12", "vm_vendor": "Oracle Corporation", "count": 3 } ], "mem": { "heap_used": "5gb", "heap_used_in_bytes": 5460944144, "heap_max": "5.8gb", "heap_max_in_bytes": 6227755008 }, "threads": 835 }, "fs": { "total": "1.7tb", "total_in_bytes": 1920365228032, "free": "499.1gb", "free_in_bytes": 535939969024, "available": "499.1gb", "available_in_bytes": 535939969024 }, "plugins": [ ], "network_types": { "transport_types": { "netty4": 3 }, "http_types": { "netty4": 3 } } } }
The jvm.options file.
...ANSWER
Answered 2021-Oct-08 at 06:38My issue is solved, It is due to the heap size issue, actually I am running the ES as service and the heap size is by default 2 GB and it is not reflecting. I just install the new service with the updated options.jvm file with heap size of 10 GB, and then run my cluster. It reflect the heap size from 2 GB to 10 GB. And my problem is solved. Thanks for the suggestions.
to check your heap size use this command.
QUESTION
Given the following class using Java 8 Optional:
ANSWER
Answered 2021-Oct-19 at 15:38There is no guaranty that the class doesn’t get loaded.
Consider JLS, §5.4:
This specification allows an implementation flexibility as to when linking activities (and, because of recursion, loading) take place, provided that all of the following properties are maintained:
…
For example, a Java Virtual Machine implementation may choose a "lazy" linkage strategy, where each symbolic reference in a class or interface (other than the symbolic references above) is resolved individually when it is used. Alternatively, an implementation may choose an "eager" linkage strategy, where all symbolic references are resolved at once when the class or interface is being verified.
Even the HotSpot JVM, which uses lazy class loading, may attempt to load the class earlier than expected, i.e. outside that unused code path, due to subtle aspects of the code, which may require the verifier to load a class, as discussed in When is a Java Class loaded?
In other words, even with this JVM implementation, small changes to the code may suddenly make it fail when the class is absent.
QUESTION
I wanted to update my JDK, so I went to AdoptOpenJDK to download one. I saw that they have moved to Adoptium, and so I went over there. There I saw that there were no options to choose the JVM, and when I downloaded the installer, it was for Hotspot. I googled it, and I found IBM Semeru. Are these JDKs/JVMs different. Is there one which is significantly faster than the other? Does it even matter?
...ANSWER
Answered 2021-Aug-18 at 14:27There's some discussion of the difference between the two from IBM over in https://github.com/docker-library/official-images/pull/10666#issuecomment-894204729:
Eclipse Temurin delivers OpenJDK + Hotspot images, and IBM Semeru Runtimes going forward will deliver both Open and Certified (JCKed) versions of OpenJDK + Eclipse OpenJ9 images.
It is a confusing story and transition, I will try to add a bit of background. AdoptOpenJDK up until now was producing OpenJDK binaries with both Hotspot and OpenJ9 VM's. With Adopt's move to Eclipse, legal restrictions prevent the new Eclipse Adoptium group from producing/releasing OpenJ9 based binaries. As a result, IBM will be producing OpenJ9 based binaries in 2 flavours, Open and Certified, both under the family name IBM Semeru Runtimes. Essentially the same binaries, released under different licenses.
So I suppose what you'll want to be looking for is comparisons between Hotspot and OpenJ9 (and I imagine any speed differences between those would be somewhat workload dependent, but there are quite a few articles online that have done actual benchmarks, such as https://www.ojalgo.org/2019/02/quick-test-to-compare-hotspot-and-openj9/).
QUESTION
In Java, method local variables live on the Stack as long as the method is being executed, hence for Method Local Inner Classes to access the method local variables, the compiler creates copies of these variables into the Heap, that's why these variables should be final or effectively final: so that the copies stored in the Heap are holding the actual valid values.
So I know Javac creates synthetic fields (fields that do not exist in the source code but are created by the compiler) inside the local inner classes to do so, and the question is how does that actually work, is it like creating a field inside the local inner class with the same as the method local variable which holds the same value as that variable so that inner class accesses that newly created one or is it something else, also what exactly does it mean for an element to be synthetic in general, apart from synthetic fields of method local inner classes? (I have read JLS, now hoping to find something more clear ?)
...ANSWER
Answered 2021-Jul-10 at 20:44The synthetic field in the class file representing the local class has a mangled name.
javap -c -s can be used to find out what javac has done.
Take the following simple example class.
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Install jvms
decompression zip and copy jvms.exe to a path what you want
run cmd or powershell as administrator
cd to folder where jvms.exe in
run jvms.exe init
Setup is complete ! Switch and install jdk see Usage Section
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