ENH: provide system() command with CStringList

- allows (for example) splitting a user string on whitespace and
  passing this to system as a list of arguments, thus bypassing any
  implicit use of 'sh'.

- system() with optional background, for spawning processes.

src/OSspecific/POSIX/POSIX.C

@@ -1406,7 +1406,11 @@ static int waitpid(const pid_t pid)
 }
 
 
-int Foam::system(const std::string& command)
+int Foam::system
+(
+    const std::string& command,
+    const bool background
+)
 {
     if (command.empty())
     {
@@ -1446,12 +1450,24 @@ int Foam::system(const std::string& command)
     }
 
 
-    // in parent - blocking wait
+    // In parent:
+
+    if (background)
+    {
+        // Started as background process
+        return 0;
+    }
+
+    // blocking wait for the child
     return waitpid(child_pid);
 }
 
 
-int Foam::system(const Foam::UList<Foam::string>& command)
+int Foam::system
+(
+    const CStringList& command,
+    const bool background
+)
 {
     const int argc = command.size();
 
@@ -1478,7 +1494,70 @@ int Foam::system(const Foam::UList<Foam::string>& command)
 
     if (child_pid == 0)
     {
-        // in child:
+        // In child:
+        // Need command and arguments separately.
+        // args is a nullptr-terminated list of c-strings
+
+        // execvp uses the current environ
+        (void) ::execvp(command[0], command.strings(1));
+
+        // obviously failed, since exec should not return at all
+        FatalErrorInFunction
+            << "exec(" << command[0] << ", ...) failed"
+            << exit(FatalError);
+    }
+
+
+    // In parent:
+
+    if (background)
+    {
+        // Started as background process
+        return 0;
+    }
+
+    // blocking wait for the child
+    return waitpid(child_pid);
+}
+
+
+int Foam::system
+(
+    const Foam::UList<Foam::string>& command,
+    const bool background
+)
+{
+    // In the future simply call the CStringList version:
+    //
+    //     const CStringList cmd(command);
+    //     return Foam::system(cmd, background);
+
+    const int argc = command.size();
+
+    if (!argc)
+    {
+        // Treat an empty command as a successful no-op.
+        // For consistency with POSIX (man sh) behaviour for (sh -c command),
+        // which is what is mostly being replicated here.
+        return 0;
+    }
+
+    // NB: use vfork, not fork!
+    // vfork behaves more like a thread and avoids copy-on-write problems
+    // triggered by fork.
+    // The normal system() command has a fork buried in it that causes
+    // issues with infiniband and openmpi etc.
+    pid_t child_pid = ::vfork();
+    if (child_pid == -1)
+    {
+        FatalErrorInFunction
+            << "vfork() failed for system command " << command[0]
+            << exit(FatalError);
+    }
+
+    if (child_pid == 0)
+    {
+        // In child:
         // Need command and arguments separately.
         // args is a nullptr-terminated list of c-strings
 
@@ -1498,7 +1577,15 @@ int Foam::system(const Foam::UList<Foam::string>& command)
     }
 
 
-    // in parent - blocking wait
+    // In parent:
+
+    if (background)
+    {
+        // Started as background process
+        return 0;
+    }
+
+    // blocking wait for the child
     return waitpid(child_pid);
 }
 

src/OpenFOAM/include/OSspecific.H

@@ -46,6 +46,10 @@ SourceFiles
 namespace Foam
 {
 
+// Forward declarations
+class CStringList;
+
+
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
 //- Return the PID of this process
@@ -206,14 +210,32 @@ bool ping(const std::string& host, const label timeOut=10);
 //  Uses vfork/execl internally.
 //  Where possible, use the list version instead.
 //
-//  Treats an empty command as a successful no-op.
-int system(const std::string& command);
+//  \param background return immediately to parent process instead of waiting
+//      for the child. Can be used (with moderation) to create background
+//      processes.
+//
+//  \note treats an empty command as a successful no-op.
+int system(const std::string& command, const bool background=false);
 
 //- Execute the specified command with arguments.
 //  Uses vfork/execvp internally
 //
-//  Treats an empty command as a successful no-op.
-int system(const UList<string>& command);
+//  \param background return immediately to parent process instead of waiting
+//      for the child. Can be used (with moderation) to create background
+//      processes.
+//
+//  \note treats an empty command as a successful no-op.
+int system(const UList<string>& command, const bool background=false);
+
+//- Execute the specified command with arguments.
+//  Uses vfork/execvp internally
+//
+//  \param background return immediately to parent process instead of waiting
+//      for the child. Can be used (with moderation) to create background
+//      processes.
+//
+//  \note treats an empty command as a successful no-op.
+int system(const CStringList& command, const bool background=false);
 
 //- Open a shared library and return handle to library.
 //  Print error message if library cannot be loaded (suppress with check=true)