fix(shm): race/deadlock in region locks

It is a valid use case to create the config programmatically at a later stage.

examples/region/keep-alive.cxx

@@ -6,10 +6,9 @@
  *                  copied verbatim in the file "LICENSE"                       *
  ********************************************************************************/
 #include <fairmq/shmem/Common.h>
-#include <fairmq/shmem/UnmanagedRegion.h>
-#include <fairmq/shmem/Segment.h>
 #include <fairmq/shmem/Monitor.h>
-
+#include <fairmq/shmem/Segment.h>
+#include <fairmq/shmem/UnmanagedRegion.h>
 #include <fairmq/tools/Unique.h>
 
 #include <fairlogger/Logger.h>
@@ -17,9 +16,8 @@
 #include <boost/algorithm/string.hpp>
 #include <boost/program_options.hpp>
 
-#include <csignal>
-
 #include <chrono>
+#include <csignal>
 #include <map>
 #include <string>
 #include <thread>
@@ -27,65 +25,117 @@
 using namespace std;
 using namespace boost::program_options;
 
-namespace
+namespace {
-{
+volatile sig_atomic_t gStopping = 0;
-    volatile sig_atomic_t gStopping = 0;
+volatile sig_atomic_t gResetContent = 0;
-}
+}   // namespace
 
-void signalHandler(int /* signal */)
+void signalHandler(int /* signal */) { gStopping = 1; }
-{
+
-    gStopping = 1;
+void resetContentHandler(int /* signal */) { gResetContent = 1; }
-}
 
 struct ShmManager
 {
-    ShmManager(uint64_t _shmId, const vector<string>& _segments, const vector<string>& _regions)
+    ShmManager(uint64_t _shmId, const vector<string>& _segments, const vector<string>& _regions, bool zero = true)
         : shmId(fair::mq::shmem::makeShmIdStr(_shmId))
+    {
+        LOG(info) << "Starting ShmManager for shmId: " << shmId;
+        LOG(info) << "Performing full reset...";
+        FullReset();
+        LOG(info) << "Done.";
+        LOG(info) << "Adding managed segments...";
+        AddSegments(_segments, zero);
+        LOG(info) << "Done.";
+        LOG(info) << "Adding unmanaged regions...";
+        AddRegions(_regions, zero);
+        LOG(info) << "Done.";
+        LOG(info) << "Shared memory is ready for use.";
+    }
+
+    void AddSegments(const vector<string>& _segments, bool zero)
     {
         for (const auto& s : _segments) {
-            vector<string> segmentConf;
+            vector<string> conf;
-            boost::algorithm::split(segmentConf, s, boost::algorithm::is_any_of(","));
+            boost::algorithm::split(conf, s, boost::algorithm::is_any_of(","));
-            if (segmentConf.size() != 2) {
+            if (conf.size() != 3) {
-                LOG(error) << "incorrect format for --segments. Expecting pairs of <id>,<size>.";
+                LOG(error) << "incorrect format for --segments. Expecting pairs of <id>,<size><numaid>.";
                 fair::mq::shmem::Monitor::Cleanup(fair::mq::shmem::ShmId{shmId});
-                throw runtime_error("incorrect format for --segments. Expecting pairs of <id>,<size>.");
+                throw runtime_error("incorrect format for --segments. Expecting pairs of <id>,<size>,<numaid>.");
             }
-            uint16_t id = stoi(segmentConf.at(0));
+            uint16_t id = stoi(conf.at(0));
-            uint64_t size = stoull(segmentConf.at(1));
+            uint64_t size = stoull(conf.at(1));
+            segmentCfgs.emplace_back(fair::mq::shmem::SegmentConfig{id, size, "rbtree_best_fit"});
+
             auto ret = segments.emplace(id, fair::mq::shmem::Segment(shmId, id, size, fair::mq::shmem::rbTreeBestFit));
             fair::mq::shmem::Segment& segment = ret.first->second;
-            LOG(info) << "Created segment " << id << " of size " << segment.GetSize() << ", starting at " << segment.GetData() << ". Locking...";
+            LOG(info) << "Created segment " << id << " of size " << segment.GetSize()
+                      << ", starting at " << segment.GetData() << ". Locking...";
             segment.Lock();
             LOG(info) << "Done.";
-            LOG(info) << "Zeroing...";
+            if (zero) {
-            segment.Zero();
+                LOG(info) << "Zeroing...";
-            LOG(info) << "Done.";
+                segment.Zero();
-        }
+                LOG(info) << "Done.";
-
-        for (const auto& r : _regions) {
-            vector<string> regionConf;
-            boost::algorithm::split(regionConf, r, boost::algorithm::is_any_of(","));
-            if (regionConf.size() != 2) {
-                LOG(error) << "incorrect format for --regions. Expecting pairs of <id>,<size>.";
-                fair::mq::shmem::Monitor::Cleanup(fair::mq::shmem::ShmId{shmId});
-                throw runtime_error("incorrect format for --regions. Expecting pairs of <id>,<size>.");
             }
-            uint16_t id = stoi(regionConf.at(0));
+        }
-            uint64_t size = stoull(regionConf.at(1));
+    }
+
+    void AddRegions(const vector<string>& _regions, bool zero)
+    {
+        for (const auto& r : _regions) {
+            vector<string> conf;
+            boost::algorithm::split(conf, r, boost::algorithm::is_any_of(","));
+            if (conf.size() != 3) {
+                LOG(error) << "incorrect format for --regions. Expecting pairs of <id>,<size>,<numaid>.";
+                fair::mq::shmem::Monitor::Cleanup(fair::mq::shmem::ShmId{shmId});
+                throw runtime_error("incorrect format for --regions. Expecting pairs of <id>,<size>,<numaid>.");
+            }
+            uint16_t id = stoi(conf.at(0));
+            uint64_t size = stoull(conf.at(1));
+            fair::mq::RegionConfig cfg;
+            cfg.id = id;
+            cfg.size = size;
+            regionCfgs.push_back(cfg);
+
             auto ret = regions.emplace(id, make_unique<fair::mq::shmem::UnmanagedRegion>(shmId, id, size));
             fair::mq::shmem::UnmanagedRegion& region = *(ret.first->second);
-            LOG(info) << "Created unamanged region " << id << " of size " << region.GetSize() << ", starting at " << region.GetData() << ". Locking...";
+            LOG(info) << "Created unamanged region " << id << " of size " << region.GetSize()
+                      << ", starting at " << region.GetData() << ". Locking...";
             region.Lock();
             LOG(info) << "Done.";
-            LOG(info) << "Zeroing...";
+            if (zero) {
-            region.Zero();
+                LOG(info) << "Zeroing...";
-            LOG(info) << "Done.";
+                region.Zero();
+                LOG(info) << "Done.";
+            }
         }
     }
 
+    bool CheckPresence()
+    {
+        for (const auto& sc : segmentCfgs) {
+            if (!(fair::mq::shmem::Monitor::SegmentIsPresent(fair::mq::shmem::ShmId{shmId}, sc.id))) {
+                return false;
+            }
+        }
+        for (const auto& rc : regionCfgs) {
+            if (!(fair::mq::shmem::Monitor::RegionIsPresent(fair::mq::shmem::ShmId{shmId}, rc.id.value()))) {
+                return false;
+            }
+        }
+        return true;
+    }
+
     void ResetContent()
     {
-        fair::mq::shmem::Monitor::ResetContent(fair::mq::shmem::ShmId{shmId});
+        fair::mq::shmem::Monitor::ResetContent(fair::mq::shmem::ShmId{shmId}, segmentCfgs, regionCfgs);
+    }
+
+    void FullReset()
+    {
+        segments.clear();
+        regions.clear();
+        fair::mq::shmem::Monitor::Cleanup(fair::mq::shmem::ShmId{shmId});
     }
 
     ~ShmManager()
@@ -97,6 +147,8 @@ struct ShmManager
     std::string shmId;
     map<uint16_t, fair::mq::shmem::Segment> segments;
     map<uint16_t, unique_ptr<fair::mq::shmem::UnmanagedRegion>> regions;
+    std::vector<fair::mq::shmem::SegmentConfig> segmentCfgs;
+    std::vector<fair::mq::RegionConfig> regionCfgs;
 };
 
 int main(int argc, char** argv)
@@ -105,8 +157,11 @@ int main(int argc, char** argv)
 
     signal(SIGINT, signalHandler);
     signal(SIGTERM, signalHandler);
+    signal(SIGUSR1, resetContentHandler);
 
     try {
+        bool nozero = false;
+        bool checkPresence = true;
         uint64_t shmId = 0;
         vector<string> segments;
         vector<string> regions;
@@ -114,8 +169,10 @@ int main(int argc, char** argv)
         options_description desc("Options");
         desc.add_options()
             ("shmid", value<uint64_t>(&shmId)->required(), "Shm id")
-            ("segments", value<vector<string>>(&segments)->multitoken()->composing(), "Segments, as <id>,<size> <id>,<size> <id>,<size> ...")
+            ("segments", value<vector<string>>(&segments)->multitoken()->composing(), "Segments, as <id>,<size>,<numaid> <id>,<size>,<numaid> <id>,<size>,<numaid> ... (numaid: -2 disabled, -1 interleave, >=0 node)")
-            ("regions",  value<vector<string>>(&regions)->multitoken()->composing(), "Regions, as <id>,<size> <id>,<size> <id>,<size> ...")
+            ("regions", value<vector<string>>(&regions)->multitoken()->composing(), "Regions, as <id>,<size> <id>,<size>,<numaid> <id>,<size>,<numaid> ...")
+            ("nozero", value<bool>(&nozero)->default_value(false)->implicit_value(true), "Do not zero segments after initialization")
+            ("check-presence", value<bool>(&checkPresence)->default_value(true)->implicit_value(true), "Check periodically if configured segments/regions are still present, and cleanup and leave if they are not")
             ("help,h", "Print help");
 
         variables_map vm;
@@ -128,15 +185,35 @@ int main(int argc, char** argv)
 
         notify(vm);
 
-        ShmManager shmManager(shmId, segments, regions);
+        ShmManager shmManager(shmId, segments, regions, !nozero);
 
-        while (!gStopping) {
+        std::thread resetContentThread([&shmManager]() {
-            std::this_thread::sleep_for(std::chrono::milliseconds(50));
+            while (!gStopping) {
+                std::this_thread::sleep_for(std::chrono::milliseconds(50));
+                if (gResetContent == 1) {
+                    LOG(info) << "Resetting content for shmId " << shmManager.shmId;
+                    shmManager.ResetContent();
+                    gResetContent = 0;
+                    LOG(info) << "Done resetting content for shmId " << shmManager.shmId;
+                }
+            }
+        });
+
+        if (checkPresence) {
+            while (!gStopping) {
+                if (shmManager.CheckPresence() == false) {
+                    LOG(error) << "Failed to find segments, exiting.";
+                    gStopping = true;
+                }
+                std::this_thread::sleep_for(std::chrono::milliseconds(500));
+            }
         }
 
+        resetContentThread.join();
+
         LOG(info) << "stopping.";
     } catch (exception& e) {
-        LOG(error) << "Unhandled Exception reached the top of main: " << e.what() << ", application will now exit";
+        LOG(error) << "Exception reached the top of main: " << e.what() << ", exiting";
         return 2;
     }
 

examples/region/sampler.cxx

@@ -76,6 +76,8 @@ struct Sampler : fair::mq::Device
 
     void ResetTask() override
     {
+        // give some time for acks to be received
+        std::this_thread::sleep_for(std::chrono::milliseconds(250));
         fRegion.reset();
         {
             std::lock_guard<std::mutex> lock(fMtx);

fairmq/plugins/config/Config.cxx

@@ -40,7 +40,7 @@ Config::Config(const string& name, Plugin::Version version, const string& mainta
                         LOG(debug) << "channel-config: Parsing channel configuration";
                         SetProperties(SuboptParser(GetProperty<vector<string>>("channel-config"), idForParser));
                     } else {
-                        LOG(warn) << "fair::mq::plugins::Config: no channels configuration provided via --mq-config or --channel-config";
+                        LOG(info) << "fair::mq::plugins::Config: no channels configuration provided via --mq-config or --channel-config";
                     }
                 } catch (exception& e) {
                     LOG(error) << e.what();

fairmq/shmem/Manager.h

@@ -397,12 +397,10 @@ class Manager
 
                 UnmanagedRegion* region = nullptr;
                 bool newRegionCreated = false;
-                {
+                std::lock_guard<std::mutex> lock(fLocalRegionsMtx);
-                    std::lock_guard<std::mutex> lock(fLocalRegionsMtx);
+                auto res = fRegions.emplace(id, std::make_unique<UnmanagedRegion>(fShmId, size, false, cfg));
-                    auto res = fRegions.emplace(id, std::make_unique<UnmanagedRegion>(fShmId, size, false, cfg));
+                newRegionCreated = res.second;
-                    newRegionCreated = res.second;
+                region = res.first->second.get();
-                    region = res.first->second.get();
-                }
                 // LOG(debug) << "Created region with id '" << id << "', path: '" << cfg.path << "', flags: '" << cfg.creationFlags << "'";
 
                 if (!newRegionCreated) {
@@ -429,7 +427,7 @@ class Manager
         }
     }
 
-    UnmanagedRegion* GetRegion(uint16_t id)
+    UnmanagedRegion* GetRegionFromCache(uint16_t id)
     {
         // NOTE: gcc optimizations. Prevent loading tls addresses many times in the fast path
         const auto &lTlCache = fTlRegionCache;
@@ -443,41 +441,40 @@ class Manager
             }
         }
 
-        boost::interprocess::scoped_lock<boost::interprocess::interprocess_mutex> shmLock(*fShmMtx);
         // slow path: check invalidation
         if (lTlCacheGen != fRegionsGen) {
             fTlRegionCache.fRegionsTLCache.clear();
         }
 
-        std::lock_guard<std::mutex> lock(fLocalRegionsMtx);
+        auto* lRegion = GetRegion(id);
-        auto* lRegion = GetRegionUnsafe(id, shmLock);
         fTlRegionCache.fRegionsTLCache.emplace_back(std::make_tuple(lRegion, id, fShmId64));
         fTlRegionCache.fRegionsTLCacheGen = fRegionsGen;
         return lRegion;
     }
 
-    UnmanagedRegion* GetRegionUnsafe(uint16_t id, boost::interprocess::scoped_lock<boost::interprocess::interprocess_mutex>& lockedShmLock)
+    UnmanagedRegion* GetRegion(uint16_t id)
     {
+        std::lock_guard<std::mutex> lock(fLocalRegionsMtx);
         // remote region could actually be a local one if a message originates from this device (has been sent out and returned)
         auto it = fRegions.find(id);
         if (it != fRegions.end()) {
             return it->second.get();
         } else {
             try {
-                // get region info
-                RegionInfo regionInfo = fShmRegions->at(id);
-                // safe to unlock now - no shm container accessed after this
-                lockedShmLock.unlock();
                 RegionConfig cfg;
-                cfg.id = id;
+                // get region info
-                cfg.creationFlags = regionInfo.fCreationFlags;
+                {
-                cfg.path = regionInfo.fPath.c_str();
+                    boost::interprocess::scoped_lock<boost::interprocess::interprocess_mutex> shmLock(*fShmMtx);
+                    RegionInfo regionInfo = fShmRegions->at(id);
+                    cfg.id = id;
+                    cfg.creationFlags = regionInfo.fCreationFlags;
+                    cfg.path = regionInfo.fPath.c_str();
+                }
                 // LOG(debug) << "Located remote region with id '" << id << "', path: '" << cfg.path << "', flags: '" << cfg.creationFlags << "'";
 
                 auto r = fRegions.emplace(id, std::make_unique<UnmanagedRegion>(fShmId, 0, true, std::move(cfg)));
                 r.first->second->InitializeQueues();
                 r.first->second->StartAckSender();
-                lockedShmLock.lock();
                 return r.first->second.get();
             } catch (std::out_of_range& oor) {
                 LOG(error) << "Could not get remote region with id '" << id << "'. Does the region creator run with the same session id?";
@@ -493,10 +490,10 @@ class Manager
     void RemoveRegion(uint16_t id)
     {
         try {
+            boost::interprocess::scoped_lock<boost::interprocess::interprocess_mutex> shmLock(*fShmMtx);
             std::lock_guard<std::mutex> lock(fLocalRegionsMtx);
             fRegions.at(id)->StopAcks();
             {
-                boost::interprocess::scoped_lock<boost::interprocess::interprocess_mutex> shmLock(*fShmMtx);
                 if (fRegions.at(id)->RemoveOnDestruction()) {
                     fShmRegions->at(id).fDestroyed = true;
                     (fEventCounter->fCount)++;
@@ -512,44 +509,73 @@ class Manager
     std::vector<fair::mq::RegionInfo> GetRegionInfo()
     {
         std::vector<fair::mq::RegionInfo> result;
-        boost::interprocess::scoped_lock<boost::interprocess::interprocess_mutex> shmLock(*fShmMtx);
+        std::map<uint64_t, RegionConfig> regionCfgs;
 
-        for (const auto& e : *fShmSegments) {
+        {
-            // make sure any segments in the session are found
+            boost::interprocess::scoped_lock<boost::interprocess::interprocess_mutex> shmLock(*fShmMtx);
-            GetSegment(e.first);
+
-            try {
+            for (const auto& [segmentId, segmentInfo] : *fShmSegments) {
+                // make sure any segments in the session are found
+                GetSegment(segmentId);
+                try {
+                    fair::mq::RegionInfo info;
+                    info.managed = true;
+                    info.id = segmentId;
+                    info.event = RegionEvent::created;
+                    info.ptr = boost::apply_visitor(SegmentAddress(), fSegments.at(segmentId));
+                    info.size = boost::apply_visitor(SegmentSize(), fSegments.at(segmentId));
+                    result.push_back(info);
+                } catch (const std::out_of_range& oor) {
+                    LOG(error) << "could not find segment with id " << segmentId;
+                    LOG(error) << oor.what();
+                }
+            }
+
+            for (const auto& [regionId, regionInfo] : *fShmRegions) {
                 fair::mq::RegionInfo info;
-                info.managed = true;
+                info.managed = false;
-                info.id = e.first;
+                info.id = regionId;
-                info.event = RegionEvent::created;
+                info.flags = regionInfo.fUserFlags;
-                info.ptr = boost::apply_visitor(SegmentAddress(), fSegments.at(e.first));
+                info.event = regionInfo.fDestroyed ? RegionEvent::destroyed : RegionEvent::created;
-                info.size = boost::apply_visitor(SegmentSize(), fSegments.at(e.first));
+                if (info.event == RegionEvent::created) {
+                    RegionConfig cfg;
+                    cfg.id = info.id;
+                    cfg.creationFlags = info.id;
+                    cfg.path = regionInfo.fPath.c_str();
+                    regionCfgs.emplace(info.id, cfg);
+                    // fill the ptr+size info after shmLock is released, to avoid constructing local region under it
+                } else {
+                    info.ptr = nullptr;
+                    info.size = 0;
+                }
                 result.push_back(info);
-            } catch (const std::out_of_range& oor) {
-                LOG(error) << "could not find segment with id " << e.first;
-                LOG(error) << oor.what();
             }
         }
 
-        for (const auto& e : *fShmRegions) {
+        // do another iteration outside of shm lock, to fill ptr+size of unmanaged regions
-            fair::mq::RegionInfo info;
+        for (auto& info : result) {
-            info.managed = false;
+            if (!info.managed && info.event == RegionEvent::created) {
-            info.id = e.first;
+                auto cfgIt = regionCfgs.find(info.id);
-            info.flags = e.second.fUserFlags;
+                if (cfgIt != regionCfgs.end()) {
-            info.event = e.second.fDestroyed ? RegionEvent::destroyed : RegionEvent::created;
+                    UnmanagedRegion* region = nullptr;
-            if (info.event == RegionEvent::created) {
+                    std::lock_guard<std::mutex> lock(fLocalRegionsMtx);
-                auto region = GetRegionUnsafe(info.id, shmLock);
+                    auto it = fRegions.find(info.id);
-                if (region) {
+                    if (it != fRegions.end()) {
+                        region = it->second.get();
+                    } else {
+                        auto r = fRegions.emplace(cfgIt->first, std::make_unique<UnmanagedRegion>(fShmId, 0, true, cfgIt->second));
+                        region = r.first->second.get();
+                        region->InitializeQueues();
+                        region->StartAckSender();
+                    }
+
                     info.ptr = region->GetData();
                     info.size = region->GetSize();
                 } else {
-                    throw std::runtime_error(tools::ToString("GetRegionInfo() could not get region with id '", info.id, "'"));
+                    info.ptr = nullptr;
+                    info.size = 0;
                 }
-            } else {
-                info.ptr = nullptr;
-                info.size = 0;
             }
-            result.push_back(info);
         }
 
         return result;

fairmq/shmem/Message.h

@@ -195,7 +195,7 @@ class Message final : public fair::mq::Message
                     fLocalPtr = nullptr;
                 }
             } else {
-                fRegionPtr = fManager.GetRegion(fMeta.fRegionId);
+                fRegionPtr = fManager.GetRegionFromCache(fMeta.fRegionId);
                 if (fRegionPtr) {
                     fLocalPtr = reinterpret_cast<char*>(fRegionPtr->GetData()) + fMeta.fHandle;
                 } else {
@@ -365,7 +365,7 @@ class Message final : public fair::mq::Message
     void ReleaseUnmanagedRegionBlock()
     {
         if (!fRegionPtr) {
-            fRegionPtr = fManager.GetRegion(fMeta.fRegionId);
+            fRegionPtr = fManager.GetRegionFromCache(fMeta.fRegionId);
         }
 
         if (fRegionPtr) {

fairmq/shmem/Monitor.cxx

@@ -23,6 +23,7 @@
 #include <boost/interprocess/ipc/message_queue.hpp>
 
 #include <csignal>
+#include <cstdio>
 #include <iostream>
 #include <iomanip>
 #include <chrono>
@@ -533,6 +534,88 @@ unsigned long Monitor::GetFreeMemory(const SessionId& sessionId, uint16_t segmen
     return GetFreeMemory(shmId, segmentId);
 }
 
+bool Monitor::SegmentIsPresent(const ShmId& shmId, uint16_t segmentId)
+{
+    using namespace boost::interprocess;
+    try {
+        bipc::managed_shared_memory managementSegment(bipc::open_read_only, std::string("fmq_" + shmId.shmId + "_mng").c_str());
+        Uint16SegmentInfoHashMap* shmSegments = managementSegment.find<Uint16SegmentInfoHashMap>(unique_instance).first;
+
+        if (!shmSegments) {
+            LOG(error) << "Found management segment, but could not locate segment info";
+            return false;
+        }
+
+        auto it = shmSegments->find(segmentId);
+        if (it != shmSegments->end()) {
+            try {
+                if (it->second.fAllocationAlgorithm == AllocationAlgorithm::rbtree_best_fit) {
+                    RBTreeBestFitSegment segment(open_read_only, std::string("fmq_" + shmId.shmId + "_m_" + std::to_string(segmentId)).c_str());
+                } else {
+                    SimpleSeqFitSegment segment(open_read_only, std::string("fmq_" + shmId.shmId + "_m_" + std::to_string(segmentId)).c_str());
+                }
+            } catch (bie&) {
+                LOG(error) << "Could not find segment with id '" << segmentId << "' for shmId '" << shmId.shmId << "'";
+                return false;
+            }
+        } else {
+            LOG(error) << "Could not find segment info for segment id '" << segmentId << "' for shmId '" << shmId.shmId << "'";
+            return false;
+        }
+    } catch (bie&) {
+        LOG(error) << "Could not find management segment for shmid '" << shmId.shmId << "'";
+        return false;
+    }
+
+    return true;
+}
+bool Monitor::SegmentIsPresent(const SessionId& sessionId, uint16_t segmentId)
+{
+    ShmId shmId{makeShmIdStr(sessionId.sessionId)};
+    return SegmentIsPresent(shmId, segmentId);
+}
+
+bool Monitor::RegionIsPresent(const ShmId& shmId, uint16_t regionId)
+{
+    using namespace boost::interprocess;
+    try {
+        bipc::managed_shared_memory managementSegment(bipc::open_read_only, std::string("fmq_" + shmId.shmId + "_mng").c_str());
+        Uint16RegionInfoHashMap* shmRegions = managementSegment.find<Uint16RegionInfoHashMap>(bipc::unique_instance).first;
+
+        if (!shmRegions) {
+            LOG(error) << "Found management segment, but could not locate region info";
+            return false;
+        }
+
+        std::string regionFileName("fmq_" + shmId.shmId + "_rg_" + to_string(regionId));
+
+        auto it = shmRegions->find(regionId);
+        if (it != shmRegions->end()) {
+            try {
+                if (it->second.fPath.empty()) {
+                    shared_memory_object object(open_only, regionFileName.c_str(), read_only);
+                }
+            } catch (bie&) {
+                LOG(error) << "Could not find region with id '" << regionId << "' for shmId '" << shmId.shmId << "'";
+                return false;
+            }
+        } else {
+            LOG(error) << "Could not find region info for region id '" << regionId << "' for shmId '" << shmId.shmId << "'";
+            return false;
+        }
+    } catch (bie&) {
+        LOG(error) << "Could not find management segment for shmid '" << shmId.shmId << "'";
+        return false;
+    }
+
+    return true;
+}
+bool Monitor::RegionIsPresent(const SessionId& sessionId, uint16_t regionId)
+{
+    ShmId shmId{makeShmIdStr(sessionId.sessionId)};
+    return RegionIsPresent(shmId, regionId);
+}
+
 void Monitor::PrintHelp()
 {
     LOG(info) << "controls: [x] close memory, "
@@ -574,7 +657,7 @@ std::vector<std::pair<std::string, bool>> Monitor::Cleanup(const ShmId& shmIdT,
 
     string managementSegmentName("fmq_" + shmId + "_mng");
     try {
-        bipc::managed_shared_memory managementSegment(bipc::open_only, managementSegmentName.c_str());
+        bipc::managed_shared_memory managementSegment(bipc::open_read_only, managementSegmentName.c_str());
 
         Uint16RegionInfoHashMap* shmRegions = managementSegment.find<Uint16RegionInfoHashMap>(bipc::unique_instance).first;
         if (shmRegions) {
@@ -660,27 +743,35 @@ void Monitor::ResetContent(const ShmId& shmIdT, bool verbose /* = true */)
         managed_shared_memory managementSegment(open_only, managementSegmentName.c_str());
 
         Uint16SegmentInfoHashMap* segmentInfos = managementSegment.find<Uint16SegmentInfoHashMap>(unique_instance).first;
-        for (const auto& s : *segmentInfos) {
+        if (segmentInfos) {
-            if (verbose) {
+            cout << "Found info for " << segmentInfos->size() << " managed segments" << endl;
-                cout << "Resetting content of segment '" << "fmq_" << shmId << "_m_" << s.first << "'..." << endl;
+            for (const auto& s : *segmentInfos) {
-            }
-            try {
-                if (s.second.fAllocationAlgorithm == AllocationAlgorithm::rbtree_best_fit) {
-                    RBTreeBestFitSegment segment(open_only, std::string("fmq_" + shmId + "_m_" + to_string(s.first)).c_str());
-                    void* ptr = segment.get_segment_manager();
-                    size_t size = segment.get_segment_manager()->get_size();
-                    new(ptr) segment_manager<char, rbtree_best_fit<mutex_family, offset_ptr<void>>, null_index>(size);
-                } else {
-                    SimpleSeqFitSegment segment(open_only, std::string("fmq_" + shmId + "_m_" + to_string(s.first)).c_str());
-                    void* ptr = segment.get_segment_manager();
-                    size_t size = segment.get_segment_manager()->get_size();
-                    new(ptr) segment_manager<char, simple_seq_fit<mutex_family, offset_ptr<void>>, null_index>(size);
-                }
-            } catch (bie& e) {
                 if (verbose) {
-                    cout << "Error resetting content of segment '" << std::string("fmq_" + shmId + "_m_" + to_string(s.first)) << "': " << e.what() << endl;
+                    cout << "Resetting content of segment '" << "fmq_" << shmId << "_m_" << s.first << "'..." << endl;
+                }
+                try {
+                    if (s.second.fAllocationAlgorithm == AllocationAlgorithm::rbtree_best_fit) {
+                        RBTreeBestFitSegment segment(open_only, std::string("fmq_" + shmId + "_m_" + to_string(s.first)).c_str());
+                        void* ptr = segment.get_segment_manager();
+                        size_t size = segment.get_segment_manager()->get_size();
+                        new(ptr) segment_manager<char, rbtree_best_fit<mutex_family, offset_ptr<void>>, null_index>(size);
+                    } else {
+                        SimpleSeqFitSegment segment(open_only, std::string("fmq_" + shmId + "_m_" + to_string(s.first)).c_str());
+                        void* ptr = segment.get_segment_manager();
+                        size_t size = segment.get_segment_manager()->get_size();
+                        new(ptr) segment_manager<char, simple_seq_fit<mutex_family, offset_ptr<void>>, null_index>(size);
+                    }
+                    if (verbose) {
+                        cout << "Done." << endl;
+                    }
+                } catch (bie& e) {
+                    if (verbose) {
+                        cout << "Error resetting content of segment '" << std::string("fmq_" + shmId + "_m_" + to_string(s.first)) << "': " << e.what() << endl;
+                    }
                 }
             }
+        } else {
+            cout << "Found management segment, but cannot locate segment info, something went wrong..." << endl;
         }
 
         Uint16RegionInfoHashMap* shmRegions = managementSegment.find<Uint16RegionInfoHashMap>(bipc::unique_instance).first;
@@ -717,13 +808,15 @@ void Monitor::ResetContent(const ShmId& shmIdT, const std::vector<SegmentConfig>
 
     std::string shmId = shmIdT.shmId;
     std::string managementSegmentName("fmq_" + shmId + "_mng");
-    // reset managed segments
-    ResetContent(shmIdT, verbose);
     // delete management segment
+    cout << "deleting management segment" << endl;
     Remove<bipc::shared_memory_object>(managementSegmentName, verbose);
     // recreate management segment
+    cout << "recreating management segment..." << endl;
     managed_shared_memory mngSegment(create_only, managementSegmentName.c_str(), kManagementSegmentSize);
+    cout << "done." << endl;
     // fill management segment with segment & region infos
+    cout << "filling management segment with managed segment configs..." << endl;
     for (const auto& s : segmentCfgs) {
         if (s.allocationAlgorithm == "rbtree_best_fit") {
             Segment::Register(shmId, s.id, AllocationAlgorithm::rbtree_best_fit);
@@ -734,9 +827,14 @@ void Monitor::ResetContent(const ShmId& shmIdT, const std::vector<SegmentConfig>
             throw MonitorError("Unknown allocation algorithm provided: " + s.allocationAlgorithm);
         }
     }
+    cout << "done." << endl;
+    cout << "filling management segment with unmanaged region configs..." << endl;
     for (const auto& r : regionCfgs) {
         fair::mq::shmem::UnmanagedRegion::Register(shmId, r);
     }
+    cout << "done." << endl;
+    // reset managed segments
+    ResetContent(shmIdT, verbose);
 }
 
 void Monitor::ResetContent(const SessionId& sessionId, const std::vector<SegmentConfig>& segmentCfgs, const std::vector<RegionConfig>& regionCfgs, bool verbose /* = true */)

fairmq/shmem/Monitor.h

@@ -119,7 +119,7 @@ class Monitor
     /// @param sessionId session id
     static std::unordered_map<uint16_t, std::vector<BufferDebugInfo>> GetDebugInfo(const SessionId& sessionId);
     /// @brief Returns the amount of free memory in the specified segment
-    /// @param sessionId shmem id
+    /// @param shmId shmem id
     /// @param segmentId segment id
     /// @throws MonitorError
     static unsigned long GetFreeMemory(const ShmId& shmId, uint16_t segmentId);
@@ -128,6 +128,23 @@ class Monitor
     /// @param segmentId segment id
     /// @throws MonitorError
     static unsigned long GetFreeMemory(const SessionId& sessionId, uint16_t segmentId);
+    /// @brief Checks if a given segment can be opened
+    /// @param shmId shmem id
+    /// @param segmentId segment id
+    static bool SegmentIsPresent(const ShmId& shmId, uint16_t segmentId);
+    /// @brief Checks if a given segment can be opened
+    /// @param sessionId session id
+    /// @param segmentId segment id
+    static bool SegmentIsPresent(const SessionId& sessionId, uint16_t segmentId);
+    /// @brief Checks if a given region can be opened
+    /// @param shmId shmem id
+    /// @param regionId region id
+    static bool RegionIsPresent(const ShmId& shmId, uint16_t regionId);
+    /// @brief Checks if a given region can be opened
+    /// @param sessionId session id
+    /// @param regionId region id
+    static bool RegionIsPresent(const SessionId& sessionId, uint16_t regionId);
+
 
     static bool PrintShm(const ShmId& shmId);
     static void ListAll(const std::string& path);