Sources/Instrumentation/MemorySampler/MemorySampler.swift

// Copyright © 2021 Elasticsearch BV
//
//   Licensed under the Apache License, Version 2.0 (the "License");
//   you may not use this file except in compliance with the License.
//   You may obtain a copy of the License at
//
//       http://www.apache.org/licenses/LICENSE-2.0
//
//   Unless required by applicable law or agreed to in writing, software
//   distributed under the License is distributed on an "AS IS" BASIS,
//   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//   See the License for the specific language governing permissions and
//   limitations under the License.

import Foundation
import OpenTelemetryApi
import OpenTelemetrySdk

public class MemorySampler {
    let meter: Meter
    var gauge: IntObserverMetric

    public init() {
        meter = OpenTelemetry.instance.meterProvider.get(instrumentationName: "Memory Sampler", instrumentationVersion: "0.0.1")
        gauge = meter.createIntObservableGauge(name: "system.memory.usage") { gauge in
            if let memoryUsage = MemorySampler.memoryFootprint() {
                gauge.observe(value: Int(memoryUsage), labels: ["state": "app"])
            }
        }
    }

    static func memoryFootprint() -> mach_vm_size_t? {
        // The `TASK_VM_INFO_COUNT` and `TASK_VM_INFO_REV1_COUNT` macros are too
        // complex for the Swift C importer, so we have to define them ourselves.
        let TASK_VM_INFO_COUNT = mach_msg_type_number_t(MemoryLayout<task_vm_info_data_t>.size / MemoryLayout<integer_t>.size)
        let TASK_VM_INFO_REV1_COUNT = mach_msg_type_number_t(MemoryLayout.offset(of: \task_vm_info_data_t.min_address)! / MemoryLayout<integer_t>.size)
        var info = task_vm_info_data_t()
        var count = TASK_VM_INFO_COUNT
        let kr = withUnsafeMutablePointer(to: &info) { infoPtr in
            infoPtr.withMemoryRebound(to: integer_t.self, capacity: Int(count)) { intPtr in
                task_info(mach_task_self_, task_flavor_t(TASK_VM_INFO), intPtr, &count)
            }
        }
        guard
            kr == KERN_SUCCESS,
            count >= TASK_VM_INFO_REV1_COUNT
        else { return nil }
        return info.phys_footprint
    }
}