Get number cores java

Get number cores java

A system may contain multiple physical CPUs (central processing units), or one or more kernels (processors). In addition, each core can have multiple threads, usually 2 (overtake—Thread TechnologyFrom Intel CPU).

Example:A system with 2 dual-core CPUs.

2 CPU X Each CPU 2 kernel =Total 4 kernels

You can determine the quantityKernelAdopt static method to provide Java virtual machineavailableProcessorsClassrun. This method is available from Java 1.4. Every Java application has oneRuntimeA single instance of a class that allows the application to interact with the environment where the application is running.

Java gets the core number

public class CPUCores < public static void main(String[] args) < int processors = Runtime.getRuntime().availableProcessors(); System.out.println("CPU cores: " + processors); > >

Output

in conclusion

As far as I said, the result is 8 because I have tested on the Intel i7 930 CPU with 4 cores and hyperthreading technology.

1 CPU X 4 kernel X 2 thread = total 8 kernels.

Note that this number is the total number of kernels available to Java applications.

refer to

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How to Optimize Java Program Performance by Determining the Number of CPU Cores

Learn how to determine the number of CPU cores available to a Java program using methods like availableProcessors(), monitoring CPU usage, and tools like Java VisualVM. Optimize your Java program performance now.

• Using availableProcessors() Method
• Understanding Logical Cores
• Monitoring CPU Usage
• Determining Number of CPUs in a System
• Using Java VisualVM
• Other code examples
• Conclusion
• How to get number of CPU cores in Java?
• How to get the number of CPU threads Java?
• How do you calculate cores?
• How many Java threads per CPU core?

Java is a widely-used programming language that is used for developing a wide range of applications. One of the key factors that can impact the performance of a Java program is the number of CPU cores available to the program. In this article, we will explain how to determine the number of CPU cores available to a Java program and how to optimize the program’s performance accordingly.

Using availableProcessors() Method

The number of cores that a Java program can utilize can be found using the method Runtime.getRuntime().availableProcessors(). This method returns the number of processors available to the Java Virtual Machine (JVM) on the system. The code snippet below demonstrates how to use the availableProcessors() method:

int numCores = Runtime.getRuntime().availableProcessors(); System.out.println("Number of CPU cores available: " + numCores); 

It’s important to note that the number of available processors may be double the number of physical CPUs if hyper-threading is enabled. Hyper-threading is a technology that allows a single physical CPU core to behave like two logical cores, which can improve performance in certain scenarios. However, it’s important to keep in mind that hyper-threading may not always result in a performance improvement and can even have a negative impact on performance in some cases.

Understanding Logical Cores

In modern Intel CPUs, each physical core can act as two logical cores, which allows for the mapping and scheduling of threads. Logical cores are not physical cores but are a way to simulate multiple cores using a single physical core. This means that a CPU with four physical cores and hyper-threading enabled will present as eight logical cores to the operating system.

It’s important to note that Java doesn’t know how many physical cores are available, only the number of logical cores, which may not be the same as the number of physical cores.

Monitoring CPU Usage

There is no direct way to find out how many CPU cores are currently free in Java. However, monitoring CPU usage can provide insight into how many cores are being utilized by a Java program. The code below demonstrates how to monitor CPU usage in Java:

OperatingSystemMXBean osBean = ManagementFactory.getPlatformMXBean(OperatingSystemMXBean.class); double cpuUsage = osBean.getSystemCpuLoad(); System.out.println("CPU usage: " + cpuUsage); 

This code retrieves the system’s CPU usage and prints it to the console. By monitoring CPU usage, you can identify if a Java program is using all available cores or if there is room for optimization.

Determining Number of CPUs in a System

The number of CPUs available to a Java Virtual Machine can be found using the method Runtime.getRuntime().availableProcessors(). This method returns the number of processors available to the JVM on the system. The code snippet below demonstrates how to use the availableProcessors() method:

int numCores = Runtime.getRuntime().availableProcessors(); System.out.println("Number of CPUs in the system: " + numCores); 

It’s important to note that the number of available processors in Java is not necessarily equal to the number of physical CPUs in the system.

Using Java VisualVM

Java VisualVM is a graphical tool that can be used to monitor and analyze Java applications. It provides a wealth of information about the JVM, including the number of threads and CPU usage. To determine the number of threads in a Java program using Java VisualVM, follow these steps:

1. Launch Java VisualVM.
2. Locate the Java process you want to monitor in the list of running processes.
3. Click on the process to open its dashboard.
4. Click on the Threads tab to view the number of threads currently running in the Java program.

Java VisualVM can also be used to monitor CPU usage, heap usage, and other metrics that can help optimize the performance of a Java program.

Other code examples

In Java , for example, java determine number of cpu cores code sample

int cores = Runtime.getRuntime().availableProcessors();

In Java , in particular, java determine number of cpu cores code example

private int getNumberOfCPUCores() < OSValidator osValidator = new OSValidator(); String command = ""; if(osValidator.isMac())< command = "sysctl -n machdep.cpu.core_count"; >else if(osValidator.isUnix())< command = "lscpu"; >else if(osValidator.isWindows()) < command = "cmd /C WMIC CPU Get /Format:List"; >Process process = null; int numberOfCores = 0; int sockets = 0; try < if(osValidator.isMac())< String[] cmd = < "/bin/sh", "-c", command>; process = Runtime.getRuntime().exec(cmd); >else < process = Runtime.getRuntime().exec(command); >> catch (IOException e) < e.printStackTrace(); >BufferedReader reader = new BufferedReader( new InputStreamReader(process.getInputStream())); String line; try < while ((line = reader.readLine()) != null) < if(osValidator.isMac())< numberOfCores = line.length() >0 ? Integer.parseInt(line) : 0; >else if (osValidator.isUnix()) < if (line.contains("Core(s) per socket:")) < numberOfCores = Integer.parseInt(line.split("\\s+")[line.split("\\s+").length - 1]); >if(line.contains("Socket(s):")) < sockets = Integer.parseInt(line.split("\\s+")[line.split("\\s+").length - 1]); >> else if (osValidator.isWindows()) < if (line.contains("NumberOfCores")) < numberOfCores = Integer.parseInt(line.split("=")[1]); >> > > catch (IOException e) < e.printStackTrace(); >if(osValidator.isUnix()) < return numberOfCores * sockets; >return numberOfCores; >

Conclusion

In conclusion, determining the number of CPU cores available to a Java program is crucial for optimizing its performance. Using the availableProcessors() method, monitoring CPU usage, and using tools like Java VisualVM can provide insight into how many cores are being utilized by a Java program and can help optimize its performance accordingly. It’s important to keep in mind that the number of available processors in Java is not necessarily equal to the number of physical CPUs in the system, and hyper-threading can impact the number of logical cores available. By following the steps outlined in this article, you can optimize the performance of your Java programs and ensure that they are running as efficiently as possible.

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Finding Number of Cores in Java

If cores is less than one, either your processor is about to die, or your JVM has a serious bug in it, or the universe is about to blow up.

Solution 2

If you want to get number of physical cores you can run cmd and terminal command and then to parse the output to get info you need.Below is shown function that returns number of physical cores .

private int getNumberOfCPUCores() < OSValidator osValidator = new OSValidator(); String command = ""; if(osValidator.isMac())< command = "sysctl -n machdep.cpu.core_count"; >else if(osValidator.isUnix())< command = "lscpu"; >else if(osValidator.isWindows()) < command = "cmd /C WMIC CPU Get /Format:List"; >Process process = null; int numberOfCores = 0; int sockets = 0; try < if(osValidator.isMac())< String[] cmd = < "/bin/sh", "-c", command>; process = Runtime.getRuntime().exec(cmd); >else < process = Runtime.getRuntime().exec(command); >> catch (IOException e) < e.printStackTrace(); >BufferedReader reader = new BufferedReader( new InputStreamReader(process.getInputStream())); String line; try < while ((line = reader.readLine()) != null) < if(osValidator.isMac())< numberOfCores = line.length() >0 ? Integer.parseInt(line) : 0; >else if (osValidator.isUnix()) < if (line.contains("Core(s) per socket:")) < numberOfCores = Integer.parseInt(line.split("\\s+")[line.split("\\s+").length - 1]); >if(line.contains("Socket(s):")) < sockets = Integer.parseInt(line.split("\\s+")[line.split("\\s+").length - 1]); >> else if (osValidator.isWindows()) < if (line.contains("NumberOfCores")) < numberOfCores = Integer.parseInt(line.split(" os.name").toLowerCase(); public static void main(String[] args) < System.out.println(OS); if (isWindows()) < System.out.println("This is Windows"); >else if (isMac()) < System.out.println("This is Mac"); >else if (isUnix()) < System.out.println("This is Unix or Linux"); >else if (isSolaris()) < System.out.println("This is Solaris"); >else < System.out.println("Your OS is not support!!"); >> public static boolean isWindows() < return (OS.indexOf("win") >= 0); > public static boolean isMac() < return (OS.indexOf("mac") >= 0); > public static boolean isUnix() < return (OS.indexOf("nix") >= 0 || OS.indexOf("nux") >= 0 || OS.indexOf("aix") > 0 ); > public static boolean isSolaris() < return (OS.indexOf("sunos") >= 0); > public static String getOS() < if (isWindows()) < return "win"; >else if (isMac()) < return "osx"; >else if (isUnix()) < return "uni"; >else if (isSolaris()) < return "sol"; >else < return "err"; >> 

Solution 3

This is an additional way to find out the number of CPU cores (and a lot of other information), but this code requires an additional dependence:

SystemInfo systemInfo = new SystemInfo(); HardwareAbstractionLayer hardwareAbstractionLayer = systemInfo.getHardware(); CentralProcessor centralProcessor = hardwareAbstractionLayer.getProcessor(); 

Get the number of logical CPUs available for processing:

centralProcessor.getLogicalProcessorCount(); 

Solution 4

If you want to dubbel check the amount of cores you have on your machine to the number your java program is giving you.

In Windows terminal (cmd): echo %NUMBER_OF_PROCESSORS%

In Mac terminal: sysctl -n hw.ncpu

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Есть ли в Java способ узнать, сколько процессоров (или ядер) установлено?

Я хочу сделать некоторую настройку для многопоточной программы. Если я знаю, сколько потоков действительно может работать параллельно, я могу сделать программу более эффективной. Есть ли способ в Java получить эту информацию?

5 ответов

Runtime.getRuntime().availableProcessors() 

Но его более полное предположение и даже упомянутое API

Это значение может изменяться во время конкретного вызова виртуального машина. Приложения, чувствительные к числу доступных поэтому процессоры должны периодически опробовать это свойство и настроить их использование ресурсов соответствующим образом.

+1 — Примечание: это не говорит приложению, сколько процессоров / ядер установлено . Но это говорит о том, сколько доступно для JVM . что действительно нужно OP.

@Stephen C: да, мне нужно именно это. Но не могли бы вы немного просветить меня: когда возможно, что не все процессоры доступны для JVM?

@Roman: Я полагаю, что когда ОС зарезервирует некоторые ядра / процессоры для какого-то другого процесса, они не будут доступны для JVM.

Одна заметка о методе доступныхпроцессоров(), в нем не проводится различие между физическим процессором и виртуальным процессором. например, если на вашем компьютере включена гиперпоточность, число будет в два раза больше физического процессора (что немного расстраивает). к сожалению, нет способа определить реальный vs. virtual cpus в чистой java.

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