private CgroupFiles findCgroupFiles()

in apm-agent-core/src/main/java/co/elastic/apm/agent/metrics/builtin/CGroupMetrics.java [84:162]
64 lines of code
17 McCabe index (conditional complexity)

    private CgroupFiles findCgroupFiles(File procSelfCgroup, File mountInfo) {
        if (!procSelfCgroup.canRead()) {
            logger.debug("Cannot find/read /proc/self/cgroup file. Cgroup metrics will not be reported.");
            return null;
        }

        String cgroupLine = null;
        try (BufferedReader fileReader = new BufferedReader(new FileReader(procSelfCgroup))) {
            String currentLine = fileReader.readLine();
            while (currentLine != null) {
                if (cgroupLine == null && currentLine.startsWith("0:")) {
                    cgroupLine = currentLine;
                }
                if (MEMORY_CGROUP.matcher(currentLine).matches()) {
                    cgroupLine = currentLine;
                    break;
                }
                currentLine = fileReader.readLine();
            }

            if (cgroupLine == null) {
                logger.warn("No /proc/self/cgroup file line matched the tested patterns. Cgroup metrics will not be reported.");
                return null;
            }

            CgroupFiles cgroupFiles;

            // Try to discover the cgroup fs path from the mountinfo file
            if (mountInfo.canRead()) {
                String mountLine = null;
                try (BufferedReader fileMountInfoReader = new BufferedReader(new FileReader(mountInfo))) {
                    mountLine = fileMountInfoReader.readLine();
                    while (mountLine != null) {
                        // cgroup v2
                        String rootCgroupFsPath = applyCgroupRegex(CGROUP2_MOUNT_POINT, mountLine);
                        if (rootCgroupFsPath != null) {
                            cgroupFiles = createCgroup2Files(cgroupLine, new File(rootCgroupFsPath));
                            if (cgroupFiles != null) {
                                return cgroupFiles;
                            }
                        }

                        // cgroup v1
                        String memoryMountPath = applyCgroupRegex(CGROUP1_MOUNT_POINT, mountLine);
                        if (memoryMountPath != null) {
                            cgroupFiles = createCgroup1Files(new File(memoryMountPath));
                            if (cgroupFiles != null) {
                                return cgroupFiles;
                            }
                        }

                        mountLine = fileMountInfoReader.readLine();
                    }
                } catch (Exception e) {
                    logger.info("Failed to discover memory mount files path based on mountinfo line '{}'.", mountLine);
                }
            } else {
                logger.info("Failed to find/read /proc/self/mountinfo file. Looking for memory files in /sys/fs/cgroup.");
            }

            // Failed to auto-discover the cgroup fs path from mountinfo, fall back to /sys/fs/cgroup
            // cgroup v2
            cgroupFiles = createCgroup2Files(cgroupLine, new File(DEFAULT_SYS_FS_CGROUP));
            if (cgroupFiles != null) {
                return cgroupFiles;
            }
            // cgroup v1
            cgroupFiles = createCgroup1Files(new File(DEFAULT_SYS_FS_CGROUP + File.pathSeparator + "memory"));
            if (cgroupFiles != null) {
                return cgroupFiles;
            }

        } catch (Exception e) {
            logger.error("Failed to discover memory mount files path based on cgroup line '" + cgroupLine +
                "'. Cgroup metrics will not be reported", e);
        }

        return null;
    }