diff --git a/src/track/heaptrack_preload.cpp b/src/track/heaptrack_preload.cpp
index 735519d..dc85a0b 100644
--- a/src/track/heaptrack_preload.cpp
+++ b/src/track/heaptrack_preload.cpp
@@ -1,325 +1,306 @@
 /*
  * Copyright 2014-2017 Milian Wolff <mail@milianw.de>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with this library; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  */
 
 #include "libheaptrack.h"
 #include "util/config.h"
 
 #include <cstdio>
 #include <cstdlib>
 #include <cstring>
 #include <dlfcn.h>
 
 #include <atomic>
 #include <type_traits>
 
 using namespace std;
 
 #if defined(_ISOC11_SOURCE)
 #define HAVE_ALIGNED_ALLOC 1
 #else
 #define HAVE_ALIGNED_ALLOC 0
 #endif
 
-extern "C" {
-__attribute__((weak)) void __libc_freeres();
-}
-namespace __gnu_cxx {
-__attribute__((weak)) extern void __freeres();
-}
-
 namespace {
 
 namespace hooks {
 
 template <typename Signature, typename Base>
 struct hook
 {
     Signature original = nullptr;
 
     void init() noexcept
     {
         auto ret = dlsym(RTLD_NEXT, Base::identifier);
         if (!ret) {
             fprintf(stderr, "Could not find original function %s\n", Base::identifier);
             abort();
         }
         original = reinterpret_cast<Signature>(ret);
     }
 
     template <typename... Args>
     auto operator()(Args... args) const noexcept -> decltype(original(args...))
     {
         return original(args...);
     }
 
     explicit operator bool() const noexcept
     {
         return original;
     }
 };
 
 #define HOOK(name)                                                                                                     \
     struct name##_t : public hook<decltype(&::name), name##_t>                                                         \
     {                                                                                                                  \
         static constexpr const char* identifier = #name;                                                               \
     } name
 
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wignored-attributes"
 
 HOOK(malloc);
 HOOK(free);
 HOOK(calloc);
 #if HAVE_CFREE
 HOOK(cfree);
 #endif
 HOOK(realloc);
 HOOK(posix_memalign);
 HOOK(valloc);
 #if HAVE_ALIGNED_ALLOC
 HOOK(aligned_alloc);
 #endif
 HOOK(dlopen);
 HOOK(dlclose);
 
 #pragma GCC diagnostic pop
 #undef HOOK
 
 /**
  * Dummy implementation, since the call to dlsym from findReal triggers a call
  * to calloc.
  *
  * This is only called at startup and will eventually be replaced by the
  * "proper" calloc implementation.
  */
 void* dummy_calloc(size_t num, size_t size) noexcept
 {
     const size_t MAX_SIZE = 1024;
     static char buf[MAX_SIZE];
     static size_t offset = 0;
     if (!offset) {
         memset(buf, 0, MAX_SIZE);
     }
     size_t oldOffset = offset;
     offset += num * size;
     if (offset >= MAX_SIZE) {
         fprintf(stderr,
                 "failed to initialize, dummy calloc buf size exhausted: "
                 "%zu requested, %zu available\n",
                 offset, MAX_SIZE);
         abort();
     }
     return buf + oldOffset;
 }
 
 void init()
 {
-    atexit([]() {
-        // free internal libstdc++ resources
-        // see also Valgrind's `--run-cxx-freeres` option
-        if (&__gnu_cxx::__freeres) {
-            __gnu_cxx::__freeres();
-        }
-        // free internal libc resources, cf: https://bugs.kde.org/show_bug.cgi?id=378765
-        // see also Valgrind's `--run-libc-freeres` option
-        if (&__libc_freeres) {
-            __libc_freeres();
-        }
-    });
     heaptrack_init(getenv("DUMP_HEAPTRACK_OUTPUT"),
                    [] {
                        hooks::calloc.original = &dummy_calloc;
                        hooks::calloc.init();
                        hooks::dlopen.init();
                        hooks::dlclose.init();
                        hooks::malloc.init();
                        hooks::free.init();
                        hooks::calloc.init();
 #if HAVE_CFREE
                        hooks::cfree.init();
 #endif
                        hooks::realloc.init();
                        hooks::posix_memalign.init();
                        hooks::valloc.init();
 #if HAVE_ALIGNED_ALLOC
                        hooks::aligned_alloc.init();
 #endif
 
                        // cleanup environment to prevent tracing of child apps
                        unsetenv("LD_PRELOAD");
                        unsetenv("DUMP_HEAPTRACK_OUTPUT");
                    },
                    nullptr, nullptr);
 }
 }
 }
 
 extern "C" {
 
 /// TODO: memalign, pvalloc, ...?
 
 void* malloc(size_t size) noexcept
 {
     if (!hooks::malloc) {
         hooks::init();
     }
 
     void* ptr = hooks::malloc(size);
     heaptrack_malloc(ptr, size);
     return ptr;
 }
 
 void free(void* ptr) noexcept
 {
     if (!hooks::free) {
         hooks::init();
     }
 
     // call handler before handing over the real free implementation
     // to ensure the ptr is not reused in-between and thus the output
     // stays consistent
     heaptrack_free(ptr);
 
     hooks::free(ptr);
 }
 
 void* realloc(void* ptr, size_t size) noexcept
 {
     if (!hooks::realloc) {
         hooks::init();
     }
 
     void* ret = hooks::realloc(ptr, size);
 
     if (ret) {
         heaptrack_realloc(ptr, size, ret);
     }
 
     return ret;
 }
 
 void* calloc(size_t num, size_t size) noexcept
 {
     if (!hooks::calloc) {
         hooks::init();
     }
 
     void* ret = hooks::calloc(num, size);
 
     if (ret) {
         heaptrack_malloc(ret, num * size);
     }
 
     return ret;
 }
 
 #if HAVE_CFREE
 void cfree(void* ptr) noexcept
 {
     if (!hooks::cfree) {
         hooks::init();
     }
 
     // call handler before handing over the real free implementation
     // to ensure the ptr is not reused in-between and thus the output
     // stays consistent
     if (ptr) {
         heaptrack_free(ptr);
     }
 
     hooks::cfree(ptr);
 }
 #endif
 
 int posix_memalign(void** memptr, size_t alignment, size_t size) noexcept
 {
     if (!hooks::posix_memalign) {
         hooks::init();
     }
 
     int ret = hooks::posix_memalign(memptr, alignment, size);
 
     if (!ret) {
         heaptrack_malloc(*memptr, size);
     }
 
     return ret;
 }
 
 #if HAVE_ALIGNED_ALLOC
 void* aligned_alloc(size_t alignment, size_t size) noexcept
 {
     if (!hooks::aligned_alloc) {
         hooks::init();
     }
 
     void* ret = hooks::aligned_alloc(alignment, size);
 
     if (ret) {
         heaptrack_malloc(ret, size);
     }
 
     return ret;
 }
 #endif
 
 void* valloc(size_t size) noexcept
 {
     if (!hooks::valloc) {
         hooks::init();
     }
 
     void* ret = hooks::valloc(size);
 
     if (ret) {
         heaptrack_malloc(ret, size);
     }
 
     return ret;
 }
 
 void* dlopen(const char* filename, int flag) noexcept
 {
     if (!hooks::dlopen) {
         hooks::init();
     }
 
     void* ret = hooks::dlopen(filename, flag);
 
     if (ret) {
         heaptrack_invalidate_module_cache();
     }
 
     return ret;
 }
 
 int dlclose(void* handle) noexcept
 {
     if (!hooks::dlclose) {
         hooks::init();
     }
 
     int ret = hooks::dlclose(handle);
 
     if (!ret) {
         heaptrack_invalidate_module_cache();
     }
 
     return ret;
 }
 }
diff --git a/src/track/libheaptrack.cpp b/src/track/libheaptrack.cpp
index af1ba5e..4ba855a 100644
--- a/src/track/libheaptrack.cpp
+++ b/src/track/libheaptrack.cpp
@@ -1,736 +1,755 @@
 /*
  * Copyright 2014-2017 Milian Wolff <mail@milianw.de>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with this library; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  */
 
 /**
  * @file libheaptrack.cpp
  *
  * @brief Collect raw heaptrack data by overloading heap allocation functions.
  */
 
 #include "libheaptrack.h"
 
 #include <cstdio>
 #include <cstdlib>
 #include <fcntl.h>
 #include <link.h>
 #include <pthread.h>
 #include <signal.h>
 #include <stdio_ext.h>
 #include <sys/file.h>
 #include <syscall.h>
 
 #include <atomic>
 #include <cinttypes>
 #include <memory>
 #include <mutex>
 #include <string>
 #include <thread>
 #include <unordered_set>
 
 #include <boost/algorithm/string/replace.hpp>
 
 #include "tracetree.h"
 #include "util/config.h"
 #include "util/libunwind_config.h"
 #include "util/linewriter.h"
 
+extern "C" {
+__attribute__((weak)) void __libc_freeres();
+}
+namespace __gnu_cxx {
+__attribute__((weak)) extern void __freeres();
+}
+
 /**
  * uncomment this to get extended debug code for known pointers
  * there are still some malloc functions I'm missing apparently,
  * related to TLS and such I guess
  */
 // #define DEBUG_MALLOC_PTRS
 
 using namespace std;
 
 namespace {
 
 using clock = chrono::steady_clock;
 chrono::time_point<clock> startTime()
 {
     static const chrono::time_point<clock> s_start = clock::now();
     return s_start;
 }
 
 chrono::milliseconds elapsedTime()
 {
     return chrono::duration_cast<chrono::milliseconds>(clock::now() - startTime());
 }
 
 __pid_t gettid()
 {
     return syscall(SYS_gettid);
 }
 
 /**
  * A per-thread handle guard to prevent infinite recursion, which should be
  * acquired before doing any special symbol handling.
  */
 struct RecursionGuard
 {
     RecursionGuard()
         : wasLocked(isActive)
     {
         isActive = true;
     }
 
     ~RecursionGuard()
     {
         isActive = wasLocked;
     }
 
     const bool wasLocked;
     static thread_local bool isActive;
 };
 
 thread_local bool RecursionGuard::isActive = false;
 
 enum DebugVerbosity
 {
     NoDebugOutput,
     MinimalOutput,
     VerboseOutput,
     VeryVerboseOutput,
 };
 
 // change this to add more debug output to stderr
 constexpr const DebugVerbosity s_debugVerbosity = NoDebugOutput;
 
 /**
  * Call this to optionally show debug information but give the compiler
  * a hand in removing it all if debug output is disabled.
  */
 template <DebugVerbosity debugLevel, typename... Args>
 inline void debugLog(const char fmt[], Args... args)
 {
     if (debugLevel <= s_debugVerbosity) {
         RecursionGuard guard;
         flockfile(stderr);
         fprintf(stderr, "heaptrack debug(%d) [%d:%d]@%" PRIu64 " ", static_cast<int>(debugLevel), getpid(), gettid(),
                 elapsedTime().count());
         fprintf(stderr, fmt, args...);
         fputc('\n', stderr);
         funlockfile(stderr);
     }
 }
 
 void printBacktrace()
 {
     if (s_debugVerbosity == NoDebugOutput)
         return;
 
 #if LIBUNWIND_HAS_UNW_GETCONTEXT && LIBUNWIND_HAS_UNW_INIT_LOCAL
     RecursionGuard guard;
 
     unw_context_t context;
     unw_getcontext(&context);
 
     unw_cursor_t cursor;
     unw_init_local(&cursor, &context);
 
     int frameNr = 0;
     while (unw_step(&cursor)) {
         ++frameNr;
         unw_word_t ip = 0;
         unw_get_reg(&cursor, UNW_REG_IP, &ip);
 
         unw_word_t sp = 0;
         unw_get_reg(&cursor, UNW_REG_SP, &sp);
 
         char symbol[256] = {"<unknown>"};
         unw_word_t offset = 0;
         unw_get_proc_name(&cursor, symbol, sizeof(symbol), &offset);
 
         fprintf(stderr, "#%-2d 0x%016" PRIxPTR " sp=0x%016" PRIxPTR " %s + 0x%" PRIxPTR "\n", frameNr,
                 static_cast<uintptr_t>(ip), static_cast<uintptr_t>(sp), symbol, static_cast<uintptr_t>(offset));
     }
 #endif
 }
 
 /**
  * Set to true in an atexit handler. In such conditions, the stop callback
  * will not be called.
  */
 atomic<bool> s_atexit{false};
 
 /**
  * Set to true in heaptrack_stop, when s_atexit was not yet set. In such conditions,
  * we always fully unload and cleanup behind ourselves
  */
 atomic<bool> s_forceCleanup{false};
 
 int createFile(const char* fileName)
 {
     string outputFileName;
     if (fileName) {
         outputFileName.assign(fileName);
     }
 
     if (outputFileName == "-" || outputFileName == "stdout") {
         debugLog<VerboseOutput>("%s", "will write to stdout");
         return fileno(stdout);
     } else if (outputFileName == "stderr") {
         debugLog<VerboseOutput>("%s", "will write to stderr");
         return fileno(stderr);
     }
 
     if (outputFileName.empty()) {
         // env var might not be set when linked directly into an executable
         outputFileName = "heaptrack.$$";
     }
 
     boost::replace_all(outputFileName, "$$", to_string(getpid()));
 
     auto out = open(outputFileName.c_str(), O_CREAT | O_WRONLY | O_CLOEXEC, 0644);
     debugLog<VerboseOutput>("will write to %s/%p\n", outputFileName.c_str(), out);
     // we do our own locking, this speeds up the writing significantly
     if (out == -1) {
         fprintf(stderr, "ERROR: failed to open heaptrack output file %s: %s (%d)\n", outputFileName.c_str(),
                 strerror(errno), errno);
     } else if (flock(out, LOCK_EX | LOCK_NB) != 0) {
         fprintf(stderr, "ERROR: failed to lock heaptrack output file %s: %s (%d)\n", outputFileName.c_str(),
                 strerror(errno), errno);
         close(out);
         return -1;
     }
 
     return out;
 }
 
 /**
  * Thread-Safe heaptrack API
  *
  * The only critical section in libheaptrack is the output of the data,
  * dl_iterate_phdr
  * calls, as well as initialization and shutdown.
  */
 class HeapTrack
 {
 public:
     HeapTrack(const RecursionGuard& /*recursionGuard*/)
     {
         debugLog<VeryVerboseOutput>("%s", "acquiring lock");
         s_lock.lock();
         debugLog<VeryVerboseOutput>("%s", "lock acquired");
     }
 
     ~HeapTrack()
     {
         debugLog<VeryVerboseOutput>("%s", "releasing lock");
         s_lock.unlock();
     }
 
     void initialize(const char* fileName, heaptrack_callback_t initBeforeCallback,
                     heaptrack_callback_initialized_t initAfterCallback, heaptrack_callback_t stopCallback)
     {
         debugLog<MinimalOutput>("initializing: %s", fileName);
         if (s_data) {
             debugLog<MinimalOutput>("%s", "already initialized");
             return;
         }
 
         if (initBeforeCallback) {
             debugLog<MinimalOutput>("%s", "calling initBeforeCallback");
             initBeforeCallback();
             debugLog<MinimalOutput>("%s", "done calling initBeforeCallback");
         }
 
         // do some once-only initializations
         static once_flag once;
         call_once(once, [] {
             debugLog<MinimalOutput>("%s", "doing once-only initialization");
             // configure libunwind for better speed
             if (unw_set_caching_policy(unw_local_addr_space, UNW_CACHE_PER_THREAD)) {
                 fprintf(stderr, "WARNING: Failed to enable per-thread libunwind caching.\n");
             }
 #if LIBUNWIND_HAS_UNW_SET_CACHE_SIZE
             if (unw_set_cache_size(unw_local_addr_space, 1024, 0)) {
                 fprintf(stderr, "WARNING: Failed to set libunwind cache size.\n");
             }
 #endif
 
             // do not trace forked child processes
             // TODO: make this configurable
             pthread_atfork(&prepare_fork, &parent_fork, &child_fork);
 
             atexit([]() {
                 if (s_forceCleanup) {
                     return;
                 }
                 debugLog<MinimalOutput>("%s", "atexit()");
+
+                // free internal libstdc++ resources
+                // see also Valgrind's `--run-cxx-freeres` option
+                if (&__gnu_cxx::__freeres) {
+                    __gnu_cxx::__freeres();
+                }
+                // free internal libc resources, cf: https://bugs.kde.org/show_bug.cgi?id=378765
+                // see also Valgrind's `--run-libc-freeres` option
+                if (&__libc_freeres) {
+                    __libc_freeres();
+                }
+
                 s_atexit.store(true);
                 heaptrack_stop();
             });
         });
 
         const auto out = createFile(fileName);
 
         if (out == -1) {
             if (stopCallback) {
                 stopCallback();
             }
             return;
         }
 
         s_data = new LockedData(out, stopCallback);
 
         writeVersion();
         writeExe();
         writeCommandLine();
         writeSystemInfo();
 
         if (initAfterCallback) {
             debugLog<MinimalOutput>("%s", "calling initAfterCallback");
             initAfterCallback(s_data->out);
             debugLog<MinimalOutput>("%s", "calling initAfterCallback done");
         }
 
         debugLog<MinimalOutput>("%s", "initialization done");
     }
 
     void shutdown()
     {
         if (!s_data) {
             return;
         }
 
         debugLog<MinimalOutput>("%s", "shutdown()");
 
         writeTimestamp();
         writeRSS();
 
         s_data->out.flush();
         s_data->out.close();
 
         // NOTE: we leak heaptrack data on exit, intentionally
         // This way, we can be sure to get all static deallocations.
         if (!s_atexit || s_forceCleanup) {
             delete s_data;
             s_data = nullptr;
         }
 
         debugLog<MinimalOutput>("%s", "shutdown() done");
     }
 
     void invalidateModuleCache()
     {
         if (!s_data) {
             return;
         }
         s_data->moduleCacheDirty = true;
     }
 
     void writeTimestamp()
     {
         if (!s_data || !s_data->out.canWrite()) {
             return;
         }
 
         auto elapsed = elapsedTime();
 
         debugLog<VeryVerboseOutput>("writeTimestamp(%" PRIx64 ")", elapsed.count());
 
         s_data->out.writeHexLine('c', static_cast<size_t>(elapsed.count()));
     }
 
     void writeRSS()
     {
         if (!s_data || !s_data->out.canWrite() || !s_data->procStatm) {
             return;
         }
 
         // read RSS in pages from statm, then rewind for next read
         size_t rss = 0;
         if (fscanf(s_data->procStatm, "%*x %zx", &rss) != 1) {
             fprintf(stderr, "WARNING: Failed to read RSS value from /proc/self/statm.\n");
             fclose(s_data->procStatm);
             s_data->procStatm = nullptr;
             return;
         }
         rewind(s_data->procStatm);
         // TODO: compare to rusage.ru_maxrss (getrusage) to find "real" peak?
         // TODO: use custom allocators with known page sizes to prevent tainting
         //       the RSS numbers with heaptrack-internal data
 
         s_data->out.writeHexLine('R', rss);
     }
 
     void writeVersion()
     {
         s_data->out.writeHexLine('v', static_cast<size_t>(HEAPTRACK_VERSION),
                                  static_cast<size_t>(HEAPTRACK_FILE_FORMAT_VERSION));
     }
 
     void writeExe()
     {
         const int BUF_SIZE = 1023;
         char buf[BUF_SIZE + 1];
         ssize_t size = readlink("/proc/self/exe", buf, BUF_SIZE);
         if (size > 0 && size < BUF_SIZE) {
             buf[size] = 0;
             s_data->out.write("x %s\n", buf);
         }
     }
 
     void writeCommandLine()
     {
         s_data->out.write("X");
         const int BUF_SIZE = 4096;
         char buf[BUF_SIZE + 1];
         auto fd = open("/proc/self/cmdline", O_RDONLY);
         int bytesRead = read(fd, buf, BUF_SIZE);
         char* end = buf + bytesRead;
         for (char* p = buf; p < end;) {
             s_data->out.write(" %s", p);
             while (*p++)
                 ; // skip until start of next 0-terminated section
         }
 
         close(fd);
         s_data->out.write("\n");
     }
 
     void writeSystemInfo()
     {
         s_data->out.writeHexLine('I', static_cast<size_t>(sysconf(_SC_PAGESIZE)),
                                  static_cast<size_t>(sysconf(_SC_PHYS_PAGES)));
     }
 
     void handleMalloc(void* ptr, size_t size, const Trace& trace)
     {
         if (!s_data || !s_data->out.canWrite()) {
             return;
         }
         updateModuleCache();
 
         const auto index = s_data->traceTree.index(
             trace, [](uintptr_t ip, uint32_t index) { return s_data->out.writeHexLine('t', ip, index); });
 
 #ifdef DEBUG_MALLOC_PTRS
         auto it = s_data->known.find(ptr);
         assert(it == s_data->known.end());
         s_data->known.insert(ptr);
 #endif
 
         s_data->out.writeHexLine('+', size, index, reinterpret_cast<uintptr_t>(ptr));
     }
 
     void handleFree(void* ptr)
     {
         if (!s_data || !s_data->out.canWrite()) {
             return;
         }
 
 #ifdef DEBUG_MALLOC_PTRS
         auto it = s_data->known.find(ptr);
         assert(it != s_data->known.end());
         s_data->known.erase(it);
 #endif
 
         s_data->out.writeHexLine('-', reinterpret_cast<uintptr_t>(ptr));
     }
 
 private:
     static int dl_iterate_phdr_callback(struct dl_phdr_info* info, size_t /*size*/, void* data)
     {
         auto heaptrack = reinterpret_cast<HeapTrack*>(data);
         const char* fileName = info->dlpi_name;
         if (!fileName || !fileName[0]) {
             fileName = "x";
         }
 
         debugLog<VerboseOutput>("dlopen_notify_callback: %s %zx", fileName, info->dlpi_addr);
 
         if (!heaptrack->s_data->out.write("m %s %zx", fileName, info->dlpi_addr)) {
             return 1;
         }
 
         for (int i = 0; i < info->dlpi_phnum; i++) {
             const auto& phdr = info->dlpi_phdr[i];
             if (phdr.p_type == PT_LOAD) {
                 if (!heaptrack->s_data->out.write(" %zx %zx", phdr.p_vaddr, phdr.p_memsz)) {
                     return 1;
                 }
             }
         }
 
         if (!heaptrack->s_data->out.write("\n")) {
             return 1;
         }
 
         return 0;
     }
 
     static void prepare_fork()
     {
         debugLog<MinimalOutput>("%s", "prepare_fork()");
         // don't do any custom malloc handling while inside fork
         RecursionGuard::isActive = true;
     }
 
     static void parent_fork()
     {
         debugLog<MinimalOutput>("%s", "parent_fork()");
         // the parent process can now continue its custom malloc tracking
         RecursionGuard::isActive = false;
     }
 
     static void child_fork()
     {
         debugLog<MinimalOutput>("%s", "child_fork()");
         // but the forked child process cleans up itself
         // this is important to prevent two processes writing to the same file
         s_data = nullptr;
         RecursionGuard::isActive = true;
     }
 
     void updateModuleCache()
     {
         if (!s_data || !s_data->out.canWrite() || !s_data->moduleCacheDirty) {
             return;
         }
         debugLog<MinimalOutput>("%s", "updateModuleCache()");
         if (!s_data->out.write("m -\n")) {
             return;
         }
         dl_iterate_phdr(&dl_iterate_phdr_callback, this);
         s_data->moduleCacheDirty = false;
     }
 
     void writeError()
     {
         debugLog<MinimalOutput>("write error %d/%s", errno, strerror(errno));
         printBacktrace();
         shutdown();
     }
 
     struct LockCheckFailed{};
 
     /**
      * To prevent deadlocks on shutdown, we try to lock from the timer thread
      * and throw an LockCheckFailed exception otherwise.
      */
     template <typename AdditionalLockCheck>
     HeapTrack(AdditionalLockCheck lockCheck)
     {
         debugLog<VeryVerboseOutput>("%s", "trying to acquire lock");
         while (!s_lock.try_lock()) {
             if (!lockCheck())
                 throw LockCheckFailed();
             this_thread::sleep_for(chrono::microseconds(1));
         }
         debugLog<VeryVerboseOutput>("%s", "lock acquired");
     }
 
     struct LockedData
     {
         LockedData(int out, heaptrack_callback_t stopCallback)
             : out(out)
             , stopCallback(stopCallback)
         {
 
             debugLog<MinimalOutput>("%s", "constructing LockedData");
             procStatm = fopen("/proc/self/statm", "r");
             if (!procStatm) {
                 fprintf(stderr, "WARNING: Failed to open /proc/self/statm for reading: %s.\n", strerror(errno));
             } else if (setvbuf(procStatm, nullptr, _IONBF, 0)) {
                 // disable buffering to ensure we read the latest values
                 fprintf(stderr, "WARNING: Failed to disable buffering for reading of /proc/self/statm: %s.\n",
                         strerror(errno));
             }
 
             // ensure this utility thread is not handling any signals
             // our host application may assume only one specific thread
             // will handle the threads, if that's not the case things
             // seemingly break in non-obvious ways.
             // see also: https://bugs.kde.org/show_bug.cgi?id=378494
             sigset_t previousMask;
             sigset_t newMask;
             sigfillset(&newMask);
             if (pthread_sigmask(SIG_SETMASK, &newMask, &previousMask) != 0) {
                 fprintf(stderr, "WARNING: Failed to block signals, disabling timer thread.\n");
                 return;
             }
 
             // the mask we set above will be inherited by the thread that we spawn below
             timerThread = thread([&]() {
                 RecursionGuard::isActive = true;
                 debugLog<MinimalOutput>("%s", "timer thread started");
 
                 // now loop and repeatedly print the timestamp and RSS usage to the data stream
                 while (!stopTimerThread) {
                     // TODO: make interval customizable
                     this_thread::sleep_for(chrono::milliseconds(10));
 
                     try {
                         HeapTrack heaptrack([&] { return !stopTimerThread.load(); });
                         heaptrack.writeTimestamp();
                         heaptrack.writeRSS();
                     } catch (LockCheckFailed) {
                         break;
                     }
                 }
             });
 
             // now restore the previous mask as if nothing ever happened
             if (pthread_sigmask(SIG_SETMASK, &previousMask, nullptr) != 0) {
                 fprintf(stderr, "WARNING: Failed to restore the signal mask.\n");
             }
         }
 
         ~LockedData()
         {
             debugLog<MinimalOutput>("%s", "destroying LockedData");
             stopTimerThread = true;
             if (timerThread.joinable()) {
                 try {
                     timerThread.join();
                 } catch (const std::system_error&) {
                 }
             }
 
             out.close();
 
             if (procStatm) {
                 fclose(procStatm);
             }
 
             if (stopCallback && (!s_atexit || s_forceCleanup)) {
                 stopCallback();
             }
             debugLog<MinimalOutput>("%s", "done destroying LockedData");
         }
 
         LineWriter out;
 
         /// /proc/self/statm file stream to read RSS value from
         FILE* procStatm = nullptr;
 
         /**
          * Calls to dlopen/dlclose mark the cache as dirty.
          * When this happened, all modules and their section addresses
          * must be found again via dl_iterate_phdr before we output the
          * next instruction pointer. Otherwise, heaptrack_interpret might
          * encounter IPs of an unknown/invalid module.
          */
         bool moduleCacheDirty = true;
 
         TraceTree traceTree;
 
         atomic<bool> stopTimerThread{false};
         thread timerThread;
 
         heaptrack_callback_t stopCallback = nullptr;
 
 #ifdef DEBUG_MALLOC_PTRS
         unordered_set<void*> known;
 #endif
     };
 
     static std::mutex s_lock;
     static LockedData* s_data;
 };
 
 std::mutex HeapTrack::s_lock;
 HeapTrack::LockedData* HeapTrack::s_data{nullptr};
 }
 extern "C" {
 
 void heaptrack_init(const char* outputFileName, heaptrack_callback_t initBeforeCallback,
                     heaptrack_callback_initialized_t initAfterCallback, heaptrack_callback_t stopCallback)
 {
     RecursionGuard guard;
     // initialize
     startTime();
 
     debugLog<MinimalOutput>("heaptrack_init(%s)", outputFileName);
 
     HeapTrack heaptrack(guard);
     heaptrack.initialize(outputFileName, initBeforeCallback, initAfterCallback, stopCallback);
 }
 
 void heaptrack_stop()
 {
     RecursionGuard guard;
 
     debugLog<MinimalOutput>("%s", "heaptrack_stop()");
 
     HeapTrack heaptrack(guard);
 
     if (!s_atexit) {
         s_forceCleanup.store(true);
     }
 
     heaptrack.shutdown();
 }
 
 void heaptrack_malloc(void* ptr, size_t size)
 {
     if (ptr && !RecursionGuard::isActive) {
         RecursionGuard guard;
 
         debugLog<VeryVerboseOutput>("heaptrack_malloc(%p, %zu)", ptr, size);
 
         Trace trace;
         trace.fill(2 + HEAPTRACK_DEBUG_BUILD);
 
         HeapTrack heaptrack(guard);
         heaptrack.handleMalloc(ptr, size, trace);
     }
 }
 
 void heaptrack_free(void* ptr)
 {
     if (ptr && !RecursionGuard::isActive) {
         RecursionGuard guard;
 
         debugLog<VeryVerboseOutput>("heaptrack_free(%p)", ptr);
 
         HeapTrack heaptrack(guard);
         heaptrack.handleFree(ptr);
     }
 }
 
 void heaptrack_realloc(void* ptr_in, size_t size, void* ptr_out)
 {
     if (ptr_out && !RecursionGuard::isActive) {
         RecursionGuard guard;
 
         debugLog<VeryVerboseOutput>("heaptrack_realloc(%p, %zu, %p)", ptr_in, size, ptr_out);
 
         Trace trace;
         trace.fill(2 + HEAPTRACK_DEBUG_BUILD);
 
         HeapTrack heaptrack(guard);
         if (ptr_in) {
             heaptrack.handleFree(ptr_in);
         }
         heaptrack.handleMalloc(ptr_out, size, trace);
     }
 }
 
 void heaptrack_invalidate_module_cache()
 {
     RecursionGuard guard;
 
     debugLog<VerboseOutput>("%s", "heaptrack_invalidate_module_cache()");
 
     HeapTrack heaptrack(guard);
     heaptrack.invalidateModuleCache();
 }
 }