Note that on Windows, the above path delimiter : should be replaced with ;. By default, this value is set to 70%. In source-file mode, compilation proceeds as follows: Any command-line options that are relevant to the compilation environment are taken into account. You can specify multiple compilation options, separated by commas or spaces. Those arrays are created during the execution of the Java code used by the Java class loaders (PlatformClassLoader and the system class loader) to load classes at dump time. To create a CDS archive using the --module-path VM option, use the following command line syntax: java -Xshare:dump -XX:SharedClassListFile=class_list_file -XX:SharedArchiveFile=shared_archive_file --module-path=path_to_modular_jar -m module_name. This reduces memory usage because the archive is memory-mapped into the address space of the processes. This difference means that the Client VM tends to flush soft references rather than grow the heap, whereas the Server VM tends to grow the heap rather than flush soft references. With no arguments, -disableassertions (-da) disables assertions in all packages and classes. The SharedArchiveConfigFile option is used to specify additional shared data to add to the archive file. container). our primary goal is to express the core algorithmic idea in an elegant and efficient manner. The default value is 5 percent of your Java heap. By default, this value is set to 40%. Here are instructions for setting up an IntelliJ-based Java programming environment Additional at sign @ prefixes to @ prefixed options act as an escape, (the first @ is removed and the rest of the arguments are presented to the launcher literally). Invoking Java with "java -version:1.5", etc. Sets the percentage of the heap (0 to 50) that's reserved as a false ceiling to reduce the possibility of promotion failure for the G1 collector. This setting replaces the -XX:DefaultMaxNewGenPercent setting. Long lists of arguments for either the VM or the program being invoked may be placed in files specified on the command-line by prefixing the filename with an @ character. Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, or g or G to indicate gigabytes. For the flags that have the ranges specified, the type, name, and the actual range is printed in the output. The actual instructions behind the values depend on the platform. The following example shows how to set the default log file (note that the identifier of the process is specified as %p): Linux and macOS: The following example shows how to set the error log to /var/log/java/java_error.log: -XX:ErrorFile=/var/log/java/java_error.log. Omitting the tag-selection defaults to a tag-set of all and a level of info. A second settings file is also provided, profile.jfc, which provides more data than the default configuration, but can have more overhead and impact performance. For the flags that don't have the range specified, the values aren't displayed in the print out. This flag only applies to the C2 compiler. White space includes a white space character, \t, \n, \r, and \f. The following examples set the thread stack size to 1024 KB in different units: This option is similar to -XX:ThreadStackSize. Sets the initial and maximum size (in bytes) of the heap for the young generation (nursery) in the generational collectors. This value must be a multiple of 1024 and greater than 2 MB. See Enable Logging with the JVM Unified Logging Framework for a description of using Unified Logging. Note: To specify an argument for a long option, you can use either --name=value or --name value. Disabling the Compact Strings feature forces the use of UTF-16 encoding as the internal representation for all Java Strings. Large pages optimize processor Translation-Lookaside Buffers. In this case, you should enclose the arguments in quotation marks, because otherwise the shell treats the semicolon as a command end. By default, the file is created in the current working directory, and it's named hotspot.log. The default value is selected at run time based on the system configuration. When you increase or decrease the percentage, ensure that you adjust the total Java heap by the same amount. The second part consists of several independent steps that print the collected information with an emphasis on different aspects of the data. You can also use the asterisk (*) as a wildcard for class and method names. This is an experimental flag. When -Xrs is used, the signal masks for SIGINT, SIGTERM, SIGHUP, and SIGQUIT aren't changed by the JVM, and signal handlers for these signals aren't installed. You will likely encounter performance degradation when this option is disabled. This flag only applies to the C1 compiler. If -jar is specified, then its argument is the name of the JAR file containing class and resource files for the application. Specifying +UnlockDiagnosticVMOptions for SharedArchiveFile is no longer needed in any configuration. The compilation option is set at the end, after the method name. Range and constraints are validated either when all flags have their values set during JVM initialization or a flag's value is changed during runtime (for example using the jcmd tool). Create a single list of classes used by all the applications that will share the shared archive file. Advanced Serviceability Options for Java: Enable gathering system information and performing extensive debugging. For example, to exclude all indexOf() methods in all classes from being compiled, use the following: The commas and periods are aliases for spaces, making it easier to pass compiler commands through a shell. The semicolons separate entries in the CLASSPATH. The following example shows how to set the maximum amount of available memory for sizing the Java heap to 2 GB: Sets the maximum amount of memory that the JVM may use for the Java heap before applying ergonomics heuristics as a percentage of the maximum amount determined as described in the -XX:MaxRAM option. Such options don't require a parameter. Windows 7: Start -> Computer -> System Properties -> Advanced system settings -> Environment Variables -> User variables -> CLASSPATH. Some operating systems expose non-DRAM memory through the file system. To avoid possible interference such as this, the -Xrs option can be used. '//www.google.com/cse/cse.js?cx=' + cx; The larger the value specified as the initial survivor space ratio, the smaller the initial survivor space size. By default, the step size is set to 16 bytes: Sets the generated code style for prefetch instructions. The default value is one second of lifetime per free megabyte in the heap. Note that after parsing the commands passed on the command line using the -XX:CompileCommand options, the JIT compiler then reads commands from the .hotspot_compiler file. You can share the same archive file across multiple applications processes. It is recommended that you keep the size for the young generation greater than 25% and less than 50% of the overall heap size. To automate the above steps 1 and 2, one can write a script such as the following: Like an AppCDS archive, the archive needs to be re-generated if the Java version has changed. The default value is the maximum amount of available memory to the JVM process or 128 GB, whichever is lower. The compiler does not enforce the optional restriction defined at the end of JLS ? Java Platform, Standard Edition Tools Reference, Release 9. The following examples show how to set the size of allocated memory to 6 MB using various units: Instead of the -Xms option to set both the minimum and initial size of the heap, you can use -XX:MinHeapSize to set the minimum size and -XX:InitialHeapSize to set the initial size. These java options control the dynamic just-in-time (JIT) compilation performed by the Java HotSpot VM. If you used our autoinstaller, you can execute with a command like. See Performance Tuning Examples for a description of using this option to keep the Java heap small by reducing the dynamic footprint for embedded applications. Sets a custom command or a series of semicolon-separated commands to run when an irrecoverable error occurs. Create a shared archive named common.jsa that contains all the classes in common.classlist: java -Xshare:dump -XX:SharedArchiveFile=common.jsa -XX:SharedClassListFile=common.classlist -cp common.jar:hello.jar:hi.jar. The -Xrs option is available to address this issue. These java options have been removed in JDK 15 and using them results in an error of: For the lists and descriptions of options removed in previous releases see the Removed Java Options section in: Java Platform, Standard Edition Tools Reference, Release 14, Java Platform, Standard Edition Tools Reference, Release 13, Java Platform, Standard Edition Tools Reference, Release 12, Java Platform, Standard Edition Tools Reference, Release 11, Java Platform, Standard Edition Tools Reference, Release 10, Java Platform, Standard Edition Tools Reference, Release 9, Java Platform, Standard Edition Tools Reference, Release 8 for Oracle JDK on Windows, Java Platform, Standard Edition Tools Reference, Release 8 for Oracle JDK on Solaris, Linux, and macOS. For example, to enable the BlockLayoutByFrequency option for the append() method of the StringBuffer class, use the following: -XX:CompileCommand=option,java/lang/StringBuffer.append,BlockLayoutByFrequency. It's possible to use compressed pointers with Java heap sizes greater than 32 GB. If the class identifies an existing file that has a .java extension, or if the --source option is specified, then source-file mode is selected. All content between the open quote and the first matching close quote are preserved by simply removing the pair of quotes. -XX:SharedArchiveConfigFile=shared_config_file. If -XX:SharedArchiveFile refers to a regular archive, then the behavior will be unchanged. Unlocks the options intended for diagnosing the JVM. By default, this option is disabled and diagnostic output isn't printed. The default value is chosen at runtime based on system configuration. To launch a class declared in a source file, run the java launcher in source-file mode. Cases where it may be beneficial to disable Compact Strings include the following: When it's known that an application overwhelmingly will be allocating multibyte character Strings, In the unexpected event where a performance regression is observed in migrating from Java SE 8 to Java SE 9 and an analysis shows that Compact Strings introduces the regression. Adaptive sizing is enabled by default with the throughput garbage collector by using the -XX:+UseParallelGC option, and the survivor space is resized according to the application behavior, starting with the initial value. 1 Although there are two ways of specifying a module in a --module-path, that is, modular JAR or exploded module, only modular JARs are supported. Our original goal for this book was to cover the 50 algorithms that every programmer should know. The operating system automatically shares the read-only pages across these processes. This let's you see which methods are getting inlined. These steps can allocate large pages for the following areas: Consequently, if you configure the nr_hugepages parameter to the size of the Java heap, then the JVM can fail in allocating the code cache areas on large pages because these areas are quite large in size. In the command line, use the at sign (@) prefix to identify an argument file that contains java options and class names. This option is enabled by default. This mode will become the default in a future release. The specified value should be a power of 2, and must be within the range of 8 and 256 (inclusive). An object's age is a measure of how many times it has survived garbage collection. You can use a single argument file, such as myargumentfile in the following example, to hold all required java arguments: You can include relative paths in argument files; however, they're relative to the current working directory and not to the paths of the argument files themselves. The 2.6 kernel supports large pages. By default, the maximum bytecode size of a trivial method is set to 6 bytes: Sets the maximum bytecode size (in bytes) of a trivial method to be inlined. The colons separate entries in the CLASSPATH. The compiled classes are executed in the context of an unnamed module, as though --add-modules=ALL-DEFAULT is in effect. var gcse = document.createElement('script'); These java options control the runtime behavior of the Java HotSpot VM. Enable this option only when you start a recording for an application that you suspect has a memory leak. You no longer have to specify -XX:+UseAppCDS with -XX:DumpLoadedClassList to produce a complete class list. The following examples show how to set the initial size of the young generation to 256 MB using various units: The -XX:NewSize option is equivalent to -Xmn. Sets the number of lines to prefetch ahead of the instance allocation pointer. The UseSHA option is used in conjunction with the UseSHA1Intrinsics, UseSHA256Intrinsics, and UseSHA512Intrinsics options. The --source option is used for cases when the source file is a "script" to be executed and the name of the source file does not follow the normal naming conventions for Java source files. It must be larger than the Java heap size. During VM start up the specified archive header will be read. By default, assertions are disabled in all packages and classes. In addition, runtime logging has also been changed to use the JVM unified logging framework. This flag only applies to the C2 compiler. This support is only available on Linux x64 platforms. The default value depends on the number of CPUs available to the JVM and the garbage collector selected. This is in addition to any other --add-module options that may be have been specified on the command line. Lines may be continued using the continuation character (\) at the end-of-line. Use the option -XX:InitialRAMPercentage instead. For example, it is possible to have a path with a space, such as c:\Program Files that can be specified as either "c:\\Program Files" or, to avoid an escape, c:\Program" "Files. ?7.6, that a type in a named package should exist in a file whose name is composed from the type name followed by the .java extension. CDS/AppCDS supports archiving classes from JAR files only. Otherwise, the old generation collection process always starts at the old generation occupancy determined by -XX:InitiatingHeapOccupancyPercent. is released under the GNU Whether they're set ergonomically, in a command line, by an input tool, or through the APIs (for example, classes contained in the package java.lang.management) the values provided to all Java Virtual Machine (JVM) command-line flags are validated. For each library or framework on the class path that requires illegal access, you have two options: If the component's maintainers have already released a fixed version that no longer uses JDK-internal APIs then you can consider upgrading to that version. Windows: Semicolons (;) separate entities in this list. Flags that control intrinsics now require the option -XX:+UnlockDiagnosticVMOptions. The following example shows how to set the young-to-old ratio to 1: Sets the initial size (in bytes) of the heap for the young generation (nursery). The replacement Unified Logging syntax is -Xlog:class+preorder=debug. In order to mitigate potential misuse of JDK_JAVA_OPTIONS behavior, options that specify the main class (such as -jar) or cause the java launcher to exit without executing the main class (such as -h) are disallowed in the environment variable. Be sure to thoroughly test and comment your code; strive for clarity; and use a style However, even though all CONSTANT_String literals in all archived classes are resolved, it might still beneficial to add additional strings that are not string literals in class files, but are likely to be used by your application at run time. The two lines are concatenated with the leading white spaces trimmed. The Java Virtual Machine (JVM) unified logging framework provides a common logging system for all components of the JVM. See jcmd. For example, when a large mount of memory is pinned by an application, it may create a shortage of regular memory and cause excessive paging in other applications and slow down the entire system. Because backslash (\) is an escape character, a backslash character must be escaped with another backslash character. Java Platform, Standard Edition Tools Reference, Release 8 for Oracle JDK on Windows. The default value is 15 for the parallel (throughput) collector. Possible mode arguments for this option include the following: Note: The -Xshare:on option is used for testing purposes only and may cause intermittent failures due to the use of address space layout randomization by the operation system. The default value for this option is 3. A Java program can't tell the difference between the two invocations. If you're expected to specify the size in bytes, then you can use no suffix, or use the suffix k or K for kilobytes (KB), m or M for megabytes (MB), or g or G for gigabytes (GB). The path to GC roots is useful for finding memory leaks, but collecting it is time-consuming. WARNING: These older versions of the JDK are provided to help developers debug issues in older systems. refers to the current directory (which contains MyProgram.java and MyProgram.class).The stdlib.jar refers to the jar file containing our standard libraries. Sets the initial amount of memory that the JVM will use for the Java heap before applying ergonomics heuristics as a percentage of the maximum amount determined as described in the -XX:MaxRAM option. For server deployments, the options -XX:InitialHeapSize and -XX:MaxHeapSize are often set to the same value. With no arguments, -enableassertions (-ea) enables assertions in all packages and classes. The UseSHA and UseSHA*Intrinsics flags are enabled by default on machines that support the corresponding instructions. Specifies the path and file name to which error data is written when an irrecoverable error occurs. A base archive is required when creating a dynamic archive. Sets the number of the stop-the-world (STW) worker threads. All other memory structures (such as the code heap, metaspace, and thread stacks) continue to reside in DRAM. This is an experimental flag. In JDK 11, Class Data Sharing (CDS) has been improved to support archiving classes from the module path. Universal Time Coordinated or Coordinated Universal Time. Memory-mapped files in these file systems bypass the page cache and provide a direct mapping of virtual memory to the physical memory on the device. For example, if a flag violates a range or a constraint check, then the JVM exits with an error: The flag -XX:+PrintFlagsRanges prints the range of all the flags. For example, to run the MyClass application with assertions enabled only in the package com.wombat.fruitbat (and any subpackages) but disabled in the class com.wombat.fruitbat.Brickbat, use the following command: Shows the splash screen with the image specified by imagepath. The following example shows how to set the initiating heap occupancy to 75%: Sets a target for the maximum GC pause time (in milliseconds). In JDK 11 and later, -XX:+UseAppCDS is obsolete and the behavior for a non-empty directory is based on the class types in the classlist. permit: This mode opens each package in each module in the run-time image to code in all unnamed modules ( such as code on the class path), if that package existed in JDK 8. The automatic testing framework can skip those flags that don't have values and aren't implemented. An open quote stops at end-of-line unless \ is the last character, which then joins the next line by removing all leading white space characters. By default, this file is created in the current working directory and named hs_err_pidpid.log where pid is the identifier of the process that encountered the error. The default value depends on the platform. Prior to JDK 11, a non-empty directory was reported as a fatal error in the following conditions: For base CDS, a non-empty directory cannot exist in the -Xbootclasspath/a path. Instead of each String object pointing to its own character array, identical String objects can point to and share the same character array. The following examples show how to set the initial and maximum size of young generation to 256 MB using various units: Instead of the -Xmn option to set both the initial and maximum size of the heap for the young generation, you can use -XX:NewSize to set the initial size and -XX:MaxNewSize to set the maximum size. Create a shared archive, named hello.jsa, that contains all the classes in hello.classlist: java -Xshare:dump -XX:SharedArchiveFile=hello.jsa -XX:SharedClassListFile=hello.classlist -cp hello.jar. See the -XX:ObjectAlignmentInBytes option. To check if your system can support large page memory, try the following: If the output shows the three "Huge" variables, then your system can support large page memory but it needs to be configured. This results in less pressure on a TLB, and memory-intensive applications may have better performance. Sets the maximum amount of memory that the JVM may use for the Java heap before applying ergonomics heuristics as a fraction of the maximum amount determined as described in the -XX:MaxRAM option for small heaps. A value of 0 implies nonstop concurrent GC cycles from the beginning until G1 adaptively sets this value. Linux only: Enables the JVM to use shared memory to set up large pages. Each log message has a level and a tag set associated with it. If you are expected to specify the percentage, then use a number from 0 to 1. If the dynamic archive was created with the default CDS archive, then the current default CDS archive will be used, and will be found relative to the current run time environment. Enables AES intrinsics. This determines the API that can be used. If the component still needs to be fixed, then you can contact its maintainers and ask them to replace their use of JDK-internal APIs with the proper exported APIs. However, as in @-files, use of a wildcard is not supported. This default settings file collects a predefined set of information with low overhead, so it has minimal impact on performance and can be used with recordings that run continuously. The largest value is 15. A nonmethod code segment containing nonmethod code, such as compiler buffers and the bytecode interpreter. The above script could be adjusted to account for the Java version as follows: Currently, we don't support concurrent dumping operations to the same CDS archive. The Windows installer downloads algs4.jar to the C:\Program Files\LIFT-CS folder; adds it the Git Bash classpath; and provides the wrapper scripts javac-algs4 and java-algs4, which classpath in algs4.jar, for use from Git Bash. General Public License, version 3 (GPLv3), 2003 California gubernatorial election order, topological sort in edge-weighted digraphs. By default, the maximum bytecode size is set to 35 bytes: Sets the maximum bytecode size (in bytes) of a cold method to be inlined. Specifying filecount=0 means that the log file shouldn't be rotated. If the base archive is not specified, the default CDS archive is used as the base archive. For example: -XX:-UseSHA256Intrinsics. The maximum amount of available memory to the JVM process is the minimum of the machine's physical memory and any constraints set by the environment (e.g. The following example shows how to set the eden/survivor space ratio to 4: Sets the desired percentage of survivor space (0 to 100) used after young garbage collection. By default, assertions are disabled in all packages and classes. File names in an argument file are relative to the current directory, not to the location of the argument file. To add several commands, either specify the -XX:CompileCommand option multiple times, or separate each argument with the new line separator (\n). No provision is made to pass any additional options to the compiler, such as -processor or -Werror. As a result, you may not realize any benefits from using compressed pointers with large Java heap sizes. The default occupancy is 85 percent. HiDPI scaled images are automatically supported and used if available. When this happens, either the OS or JVM reverts to using regular pages. Use -Xlog:os+container=trace for maximum logging of container information. The -Xloggc option overrides -verbose:gc if both are given with the same java command. In the latter case, the value of the -Xmx option has a significant effect on how quickly soft references are garbage collected. See JEP 330: Launch Single-File Source-Code Programs for complete details. Specifying-XX:+UseAESIntrinsics is equivalent to also enabling -XX:+UseAES. Only the specified methods are compiled. On a system with 4 GB of physical RAM (or less), the following makes all the memory sharable: # echo 4294967295 > /proc/sys/kernel/shmmax. Archived OpenJDK General-Availability Releases.