Fix rx arping socket bind (#646)

* first tries with a process intead of thread for rx_arping

* Moving delete pointer of udp socket to stopReciever,so rx_arping can only be set when udp socket is closed

* refactoring and formatting

* unused variable processId

* ignore sigchild to prevent zombie from child processes being killed

python/slsdet/detector.py

@@ -267,7 +267,7 @@ class Detector(CppDetectorApi):
     @element
     def rx_threads(self):
         """
-        Get thread ids from the receiver in order of [parent, tcp, listener 0, processor 0, streamer 0, listener 1, processor 1, streamer 1, arping]. 
+        Get kernel thread ids from the receiver in order of [parent, tcp, listener 0, processor 0, streamer 0, listener 1, processor 1, streamer 1, arping]. 
         
         Note
         -----

slsDetectorSoftware/include/sls/Detector.h

@@ -943,9 +943,10 @@ class Detector {
     /** Client IP Address that last communicated with the receiver */
     Result<IpAddr> getRxLastClientIP(Positions pos = {}) const;
 
-    /** Get thread ids from the receiver in order of [parent, tcp, listener 0,
-     * processor 0, streamer 0, listener 1, processor 1, streamer 1, arping]. If
-     * no streamer yet or there is no second interface, it gives 0 in its place.
+    /** Get kernel thread ids from the receiver in order of [parent, tcp,
+     * listener 0, processor 0, streamer 0, listener 1, processor 1, streamer 1,
+     * arping]. If no streamer yet or there is no second interface, it gives 0
+     * in its place.
      */
     Result<std::array<pid_t, NUM_RX_THREAD_IDS>>
     getRxThreadIds(Positions pos = {}) const;

slsDetectorSoftware/src/CmdProxy.h

@@ -1767,11 +1767,12 @@ class CmdProxy {
         rx_lastclient, getRxLastClientIP,
         "\n\tClient IP Address that last communicated with the receiver.");
 
-    GET_COMMAND(rx_threads, getRxThreadIds,
-                "\n\tGet thread ids from the receiver in order of [parent, "
-                "tcp, listener 0, processor 0, streamer 0, listener 1, "
-                "processor 1, streamer 1, arping]. If no streamer yet or there "
-                "is no second interface, it gives 0 in its place.");
+    GET_COMMAND(
+        rx_threads, getRxThreadIds,
+        "\n\tGet kernel thread ids from the receiver in order of [parent, "
+        "tcp, listener 0, processor 0, streamer 0, listener 1, "
+        "processor 1, streamer 1, arping]. If no streamer yet or there "
+        "is no second interface, it gives 0 in its place.");
 
     INTEGER_COMMAND_VEC_ID(rx_arping, getRxArping, setRxArping, StringTo<int>,
                            "[0, 1]\n\tStarts a thread in slsReceiver to arping "

slsReceiverSoftware/src/Arping.cpp

@@ -4,6 +4,8 @@
 #include "Arping.h"
 
 #include <chrono>
+#include <signal.h>
+#include <thread>
 #include <unistd.h>
 
 namespace sls {
@@ -18,7 +20,7 @@ Arping::Arping() {}
 
 Arping::~Arping() {
     if (IsRunning()) {
-        StopThread();
+        StopProcess();
     }
 }
 
@@ -33,59 +35,66 @@ void Arping::SetInterfacesAndIps(const int index, const std::string &interface,
     // create commands to arping
     std::ostringstream os;
     os << "arping -c 1 -U -I " << interface << " " << ip;
-    // to read error messages
-    os << " 2>&1";
     std::string cmd = os.str();
     commands[index] = cmd;
 }
 
-pid_t Arping::GetThreadId() const { return threadId; }
+pid_t Arping::GetProcessId() const { return childPid; }
 
 bool Arping::IsRunning() const { return runningFlag; }
 
-void Arping::StartThread() {
+void Arping::StartProcess() {
     TestCommands();
-    try {
-        t = std::thread(&Arping::ThreadExecution, this);
-    } catch (...) {
-        throw RuntimeError("Could not start arping thread");
+
+    // to prevent zombies from child processes being killed
+    signal(SIGCHLD, SIG_IGN);
+
+    // Needs to be a fork and udp socket deleted after Listening threads
+    // done running to prevent udp socket cannot bind because of popen
+    // that forks
+    childPid = fork();
+    // child process
+    if (childPid == 0) {
+        LOG(logINFOBLUE) << "Created [ Arping Process, Tid: " << gettid()
+                         << " ]";
+        ProcessExecution();
+    }
+    // parent process
+    else if (childPid > 0) {
+        runningFlag = true;
+    }
+    // error
+    else {
+        throw RuntimeError("Could not start arping Process");
     }
-    runningFlag = true;
 }
 
-void Arping::StopThread() {
+void Arping::StopProcess() {
+    LOG(logINFOBLUE) << "Exiting [ Arping Process ]";
+
+    if (kill(childPid, SIGTERM)) {
+        throw RuntimeError("Could not kill the arping Process");
+    }
     runningFlag = false;
-    t.join();
 }
 
-void Arping::ThreadExecution() {
-    threadId = gettid();
-    LOG(logINFOBLUE) << "Created [ Arping Thread, Tid: " << threadId << " ]";
-
-    while (runningFlag) {
+void Arping::ProcessExecution() {
+    while (true) {
         std::string error = ExecuteCommands();
-        // just print (was already tested at thread start)
+        // just print (was already tested at Process start)
         if (!error.empty()) {
             LOG(logERROR) << error;
         }
 
-        // wait for 60s as long as thread not killed
-        int nsecs = 0;
-        while (runningFlag && nsecs != 60) {
-            std::this_thread::sleep_for(std::chrono::seconds(1));
-            ++nsecs;
-        }
+        std::this_thread::sleep_for(std::chrono::seconds(timeIntervalSeconds));
     }
-
-    LOG(logINFOBLUE) << "Exiting [ Arping Thread, Tid: " << threadId << " ]";
-    threadId = 0;
 }
 
 void Arping::TestCommands() {
     // atleast one interface must be set up
     if (commands[0].empty()) {
         throw RuntimeError(
-            "Could not arping. Interface not set up in apring thread");
+            "Could not arping. Interface not set up in arping Process");
     }
     // test if arping commands throw an error
     std::string error = ExecuteCommands();
@@ -101,7 +110,7 @@ std::string Arping::ExecuteCommands() {
         if (cmd.empty())
             continue;
 
-        LOG(logDEBUG) << "Executing Arping Command: " << cmd;
+        LOG(logDEBUG1) << "Executing Arping Command: " << cmd;
 
         // execute command
         FILE *sysFile = popen(cmd.c_str(), "r");

slsReceiverSoftware/src/Arping.h

@@ -2,15 +2,15 @@
 // Copyright (C) 2021 Contributors to the SLS Detector Package
 #pragma once
 /**
- *@short creates/destroys an ARPing thread to arping the interfaces slsReceiver
-is listening to.
+ *@short creates/destroys an ARPing child process to arping the interfaces
+slsReceiver is listening to.
  */
 
 #include "receiver_defs.h"
 #include "sls/logger.h"
 
 #include <atomic>
-#include <thread>
+#include <unistd.h>
 
 namespace sls {
 
@@ -22,21 +22,21 @@ class Arping {
 
     void SetInterfacesAndIps(const int index, const std::string &interface,
                              const std::string &ip);
-    pid_t GetThreadId() const;
+    pid_t GetProcessId() const;
     bool IsRunning() const;
-    void StartThread();
-    void StopThread();
+    void StartProcess();
+    void StopProcess();
 
   private:
     void TestCommands();
     std::string ExecuteCommands();
-    void ThreadExecution();
+    void ProcessExecution();
 
     std::vector<std::string> commands =
         std::vector<std::string>(MAX_NUMBER_OF_LISTENING_THREADS);
     std::atomic<bool> runningFlag{false};
-    std::thread t;
-    std::atomic<pid_t> threadId{0};
+    std::atomic<pid_t> childPid{0};
+    static const int timeIntervalSeconds = 60;
 };
 
 } // namespace sls

slsReceiverSoftware/src/Implementation.cpp

@@ -351,19 +351,19 @@ std::array<pid_t, NUM_RX_THREAD_IDS> Implementation::getThreadIds() const {
             retval[id++] = 0;
         }
     }
-    retval[NUM_RX_THREAD_IDS - 1] = arping.GetThreadId();
+    retval[NUM_RX_THREAD_IDS - 1] = arping.GetProcessId();
     return retval;
 }
 
 bool Implementation::getArping() const { return arping.IsRunning(); }
 
-pid_t Implementation::getArpingThreadId() const { return arping.GetThreadId(); }
+pid_t Implementation::getArpingProcessId() const { return arping.GetProcessId(); }
 
 void Implementation::setArping(const bool i,
                                const std::vector<std::string> ips) {
     if (i != arping.IsRunning()) {
         if (!i) {
-            arping.StopThread();
+            arping.StopProcess();
         } else {
             // setup interface
             for (int i = 0; i != generalData->numUDPInterfaces; ++i) {
@@ -374,7 +374,7 @@ void Implementation::setArping(const bool i,
                 }
                 arping.SetInterfacesAndIps(i, eth[i], ips[i]);
             }
-            arping.StartThread();
+            arping.StartProcess();
         }
     }
 }
@@ -713,6 +713,10 @@ void Implementation::stopReceiver() {
         std::this_thread::sleep_for(std::chrono::milliseconds(5));
     }
 
+    // delete the udp sockets
+    for (const auto &it : listener)
+        it->DeleteUDPSocket();
+
     if (fileWriteEnable && modulePos == 0) {
         // master and virtual file (hdf5)
         StartMasterWriter();

slsReceiverSoftware/src/Implementation.h

@@ -54,7 +54,7 @@ class Implementation : private virtual slsDetectorDefs {
     void setThreadIds(const pid_t parentTid, const pid_t tcpTid);
     std::array<pid_t, NUM_RX_THREAD_IDS> getThreadIds() const;
     bool getArping() const;
-    pid_t getArpingThreadId() const;
+    pid_t getArpingProcessId() const;
     void setArping(const bool i, const std::vector<std::string> ips);
     ROI getReceiverROI() const;
     void setReceiverROI(const ROI arg);

slsReceiverSoftware/src/Listener.cpp

@@ -184,6 +184,13 @@ void Listener::ShutDownUDPSocket() {
     }
 }
 
+void Listener::DeleteUDPSocket() {
+    if (udpSocket) {
+        udpSocket.reset();
+        LOG(logINFO) << "Closed UDP port " << udpPortNumber;
+    }
+}
+
 void Listener::CreateDummySocketForUDPSocketBufferSize(int s, int &actualSize) {
     // custom setup (s != 0)
     // default setup at startup (s = 0)

slsReceiverSoftware/src/Listener.h

@@ -50,6 +50,7 @@ class Listener : private virtual slsDetectorDefs, public ThreadObject {
     void ResetParametersforNewAcquisition();
     void CreateUDPSocket(int &actualSize);
     void ShutDownUDPSocket();
+    void DeleteUDPSocket();
     /** to set & get actual buffer size */
     void CreateDummySocketForUDPSocketBufferSize(int s, int &actualSize);