Merge "libprocessgroup: Add sendSignalToProcessGroup"

// that it only returns 0 in the case that the cgroup exists and it contains no processes.

int killProcessGroupOnce(uid_t uid, int initialPid, int signal, int* max_processes = nullptr);

// Sends the provided signal to all members of a process group, but does not wait for processes to

// exit, or for the cgroup to be removed. Callers should also ensure that killProcessGroup is called

// later to ensure the cgroup is fully removed, otherwise system resources may leak.

int sendSignalToProcessGroup(uid_t uid, int initialPid, int signal);

int createProcessGroup(uid_t uid, int initialPid, bool memControl = false);

// Set various properties of a process group. For these functions to work, the process group must

    return KillProcessGroup(uid, initialPid, signal, 0 /*retries*/, max_processes);

}

int sendSignalToProcessGroup(uid_t uid, int initialPid, int signal) {

    std::string hierarchy_root_path;

    if (CgroupsAvailable()) {

        CgroupGetControllerPath(CGROUPV2_CONTROLLER_NAME, &hierarchy_root_path);

    }

    const char* cgroup = hierarchy_root_path.c_str();

    return DoKillProcessGroupOnce(cgroup, uid, initialPid, signal);

}

static int createProcessGroupInternal(uid_t uid, int initialPid, std::string cgroup,

                                      bool activate_controllers) {

    auto uid_path = ConvertUidToPath(cgroup.c_str(), uid);