estimateMaxDirectMemory() — netty Function Reference

Architecture documentation for the estimateMaxDirectMemory() function in PlatformDependent.java from the netty codebase.

Function java CommonUtil Internal

Entity Profile

CommonUtil→ Internal→ estimateMaxDirectMemory() — netty Function Reference

Dependency Diagram

graph TD
  5a915619_2268_5b50_46c5_9b521ab8b6c7["estimateMaxDirectMemory()"]
  2e66d079_807f_6785_864f_73ab09fbc515["PlatformDependent"]
  5a915619_2268_5b50_46c5_9b521ab8b6c7 -->|defined in| 2e66d079_807f_6785_864f_73ab09fbc515
  style 5a915619_2268_5b50_46c5_9b521ab8b6c7 fill:#6366f1,stroke:#818cf8,color:#fff

Relationship Graph

Source Code

common/src/main/java/io/netty/util/internal/PlatformDependent.java lines 1474–1533

    @SuppressWarnings("unchecked")
    public static long estimateMaxDirectMemory() {
        long maxDirectMemory = PlatformDependent0.bitsMaxDirectMemory();
        if (maxDirectMemory > 0) {
            return maxDirectMemory;
        }

        try {
            // Now try to get the JVM option (-XX:MaxDirectMemorySize) and parse it.
            // Note that we are using reflection because Android doesn't have these classes.
            ClassLoader systemClassLoader = getSystemClassLoader();
            Class<?> mgmtFactoryClass = Class.forName(
                    "java.lang.management.ManagementFactory", true, systemClassLoader);
            Class<?> runtimeClass = Class.forName(
                    "java.lang.management.RuntimeMXBean", true, systemClassLoader);

            MethodHandles.Lookup lookup = MethodHandles.publicLookup();
            MethodHandle getRuntime = lookup.findStatic(
                    mgmtFactoryClass, "getRuntimeMXBean", methodType(runtimeClass));
            MethodHandle getInputArguments = lookup.findVirtual(
                    runtimeClass, "getInputArguments", methodType(List.class));
            List<String> vmArgs = (List<String>) getInputArguments.invoke(getRuntime.invoke());

            Pattern maxDirectMemorySizeArgPattern = getMaxDirectMemorySizeArgPattern();

            for (int i = vmArgs.size() - 1; i >= 0; i --) {
                Matcher m = maxDirectMemorySizeArgPattern.matcher(vmArgs.get(i));
                if (!m.matches()) {
                    continue;
                }

                maxDirectMemory = Long.parseLong(m.group(1));
                switch (m.group(2).charAt(0)) {
                    case 'k': case 'K':
                        maxDirectMemory *= 1024;
                        break;
                    case 'm': case 'M':
                        maxDirectMemory *= 1024 * 1024;
                        break;
                    case 'g': case 'G':
                        maxDirectMemory *= 1024 * 1024 * 1024;
                        break;
                    default:
                        break;
                }
                break;
            }
        } catch (Throwable ignored) {
            // Ignore
        }

        if (maxDirectMemory <= 0) {
            maxDirectMemory = Runtime.getRuntime().maxMemory();
            logger.debug("maxDirectMemory: {} bytes (maybe)", maxDirectMemory);
        } else {
            logger.debug("maxDirectMemory: {} bytes", maxDirectMemory);
        }

        return maxDirectMemory;
    }