Fix for subjob spawning with FIFOs

Generators/include/Generators/GeneratorFileOrCmd.h

@@ -46,6 +46,12 @@ struct GeneratorFileOrCmd {
    *   execute, but should not include pipes.
    */
   void setCmd(const std::string& cmd) { mCmd = cmd; }
+  /**
+   * Set command child process PID
+   *
+   * @param cmdPid child process PID.
+   */
+  void setCmdPid(const pid_t cmdPid) { mCmdPid = cmdPid; }
   /**
    * Set the number of events that a background command should
    * generate. This should come from @c SimConfig::getNEents.
@@ -132,7 +138,14 @@ struct GeneratorFileOrCmd {
    * @return true if the background command line was executed, false
    * otherwise.
    */
-  virtual bool executeCmdLine(const std::string& cmd) const;
+  virtual bool executeCmdLine(const std::string& cmd);
+  /**
+   * Terminates the background command using PID of the child
+   * process generated by fork.
+   *
+   * @return true if the process was terminated successfully
+   */
+  virtual bool terminateCmd();
   /**
    * Create a temporary file (and close it immediately).  On success,
    * the list of file names is cleared and the name of the temporary
@@ -236,6 +249,10 @@ struct GeneratorFileOrCmd {
    * Time in miliseconds between each wait for data
    */
   int mWait = 500;
+  /**
+   * PID of the background command
+   */
+  int mCmdPid = -1;
 };
 
 } // namespace eventgen

Generators/src/GeneratorFileOrCmd.cxx

@@ -16,7 +16,9 @@
 // For fifo's and system call
 #include <cstdlib>
 #include <sys/types.h> // POSIX only
-#include <sys/stat.h>  // POISX only
+#include <sys/stat.h>  // POSIX only
+#include <csignal>
+#include <sys/wait.h>
 #include <cstdio>
 // For filesystem operations
 #include <filesystem>
@@ -115,14 +117,52 @@ std::string GeneratorFileOrCmd::makeCmdLine() const
   return s.str();
 }
 // -----------------------------------------------------------------
-bool GeneratorFileOrCmd::executeCmdLine(const std::string& cmd) const
+bool GeneratorFileOrCmd::executeCmdLine(const std::string& cmd)
 {
   LOG(info) << "Command line to execute: \"" << cmd << "\"";
-  int ret = std::system(cmd.c_str());
-  if (ret != 0) {
-    LOG(fatal) << "Failed to spawn \"" << cmd << "\"";
+  // Fork a new process
+  pid_t pid = fork();
+  if (pid == -1) {
+    LOG(fatal) << "Failed to fork process: " << std::strerror(errno);
     return false;
   }
+
+  if (pid == 0) {
+    // Child process
+    setsid();
+    execl("/bin/sh", "sh", "-c", cmd.c_str(), (char*)nullptr);
+    // If execl returns, there was an error, otherwise following lines will not be executed
+    LOG(fatal) << "Failed to execute command: " << std::strerror(errno);
+    _exit(EXIT_FAILURE);
+  } else {
+    // Parent process
+    setCmdPid(pid);
+    LOG(info) << "Child spawned process group is running with PID: " << mCmdPid;
+  }
+  return true;
+}
+// -----------------------------------------------------------------
+bool GeneratorFileOrCmd::terminateCmd()
+{
+  if (mCmdPid == -1) {
+    LOG(info) << "No command is currently running";
+    return false;
+  }
+
+  LOG(info) << "Terminating process ID group " << mCmdPid;
+  if (kill(-mCmdPid, SIGKILL) == -1) {
+    LOG(fatal) << "Failed to kill process: " << std::strerror(errno);
+    return false;
+  }
+
+  // Wait for the process to terminate
+  int status;
+  if (waitpid(mCmdPid, &status, 0) == -1) {
+    LOG(fatal) << "Failed to wait for process termination: " << std::strerror(errno);
+    return false;
+  }
+
+  mCmdPid = -1; // Reset the process ID
   return true;
 }
 // -----------------------------------------------------------------

Generators/src/GeneratorHepMC.cxx

@@ -65,6 +65,12 @@ GeneratorHepMC::~GeneratorHepMC()
   if (mEvent) {
     delete mEvent;
   }
+  if (not mCmd.empty()) {
+    // Must be executed before removing the temporary file
+    // otherwise the current child process might still be writing on it
+    // causing unwanted stdout messages which could slow down the system
+    terminateCmd();
+  }
   removeTemp();
 }