vm.measureMemory([options])

测量 V8 已知的内存并被当前 V8 隔离已知的所有上下文或主上下文使用。

• options <Object> 可选的。
  • mode <string> 'summary' 或 'detailed'。 在摘要模式下，只会返回为主上下文测量的内存。 在详细模式下，将返回为当前 V8 隔离已知的所有上下文测量的内存。 默认值: 'summary'
  • execution <string> 'default' 或 'eager'。 在默认执行情况下，promise 将在下一次计划的垃圾收集开始后才会解决，这可能需要一段时间（如果程序在下一次 GC 之前退出，则永远不会）。 在快速执行情况下，GC 将立即启动以测量内存。 默认值: 'default'
• 返回: <Promise> 如果成功测量内存，则 promise 将使用包含内存使用信息的对象进行解决。

返回的 Promise 可以解决的对象的格式特定于 V8 引擎，并且可能会从 V8 的一个版本更改为下一个版本。

返回的结果与 v8.getHeapSpaceStatistics() 返回的统计数据不同，vm.measureMemory() 测量的是 V8 引擎当前实例中每个 V8 特定上下文可访问的内存，而 v8.getHeapSpaceStatistics() 的结果测量的是当前V8中每个堆空间占用的内存实例。

const vm = require('node:vm');
// 测量主上下文使用的内存。
vm.measureMemory({ mode: 'summary' })
  // 这和 vm.measureMemory() 一样
  .then((result) => {
    // 当前格式为：
    // {
    //   total: {
    //      jsMemoryEstimate: 2418479, jsMemoryRange: [ 2418479, 2745799 ]
    //    }
    // }
    console.log(result);
  });

const context = vm.createContext({ a: 1 });
vm.measureMemory({ mode: 'detailed', execution: 'eager' })
  .then((result) => {
    // 在此处引用上下文，
    // 以便在测量完成之前不会对其进行 GC。
    console.log(context.a);
    // {
    //   total: {
    //     jsMemoryEstimate: 2574732,
    //     jsMemoryRange: [ 2574732, 2904372 ]
    //   },
    //   current: {
    //     jsMemoryEstimate: 2438996,
    //     jsMemoryRange: [ 2438996, 2768636 ]
    //   },
    //   other: [
    //     {
    //       jsMemoryEstimate: 135736,
    //       jsMemoryRange: [ 135736, 465376 ]
    //     }
    //   ]
    // }
    console.log(result);
  });

Measure the memory known to V8 and used by all contexts known to the current V8 isolate, or the main context.

• options <Object> Optional.
  • mode <string> Either 'summary' or 'detailed'. In summary mode, only the memory measured for the main context will be returned. In detailed mode, the memory measured for all contexts known to the current V8 isolate will be returned. Default: 'summary'
  • execution <string> Either 'default' or 'eager'. With default execution, the promise will not resolve until after the next scheduled garbage collection starts, which may take a while (or never if the program exits before the next GC). With eager execution, the GC will be started right away to measure the memory. Default: 'default'
• Returns: <Promise> If the memory is successfully measured the promise will resolve with an object containing information about the memory usage.

The format of the object that the returned Promise may resolve with is specific to the V8 engine and may change from one version of V8 to the next.

The returned result is different from the statistics returned by v8.getHeapSpaceStatistics() in that vm.measureMemory() measure the memory reachable by each V8 specific contexts in the current instance of the V8 engine, while the result of v8.getHeapSpaceStatistics() measure the memory occupied by each heap space in the current V8 instance.

const vm = require('node:vm');
// Measure the memory used by the main context.
vm.measureMemory({ mode: 'summary' })
  // This is the same as vm.measureMemory()
  .then((result) => {
    // The current format is:
    // {
    //   total: {
    //      jsMemoryEstimate: 2418479, jsMemoryRange: [ 2418479, 2745799 ]
    //    }
    // }
    console.log(result);
  });

const context = vm.createContext({ a: 1 });
vm.measureMemory({ mode: 'detailed', execution: 'eager' })
  .then((result) => {
    // Reference the context here so that it won't be GC'ed
    // until the measurement is complete.
    console.log(context.a);
    // {
    //   total: {
    //     jsMemoryEstimate: 2574732,
    //     jsMemoryRange: [ 2574732, 2904372 ]
    //   },
    //   current: {
    //     jsMemoryEstimate: 2438996,
    //     jsMemoryRange: [ 2438996, 2768636 ]
    //   },
    //   other: [
    //     {
    //       jsMemoryEstimate: 135736,
    //       jsMemoryRange: [ 135736, 465376 ]
    //     }
    //   ]
    // }
    console.log(result);
  });