TPluginManager.cxx

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// @(#)root/base:$Id$
// Author: Fons Rademakers   26/1/2002

/*************************************************************************
 * Copyright (C) 1995-2002, Rene Brun and Fons Rademakers.               *
 * All rights reserved.                                                  *
 *                                                                       *
 * For the licensing terms see $ROOTSYS/LICENSE.                         *
 * For the list of contributors see $ROOTSYS/README/CREDITS.             *
 *************************************************************************/

/** \class TPluginManager
\ingroup Base

This class implements a plugin library manager.

It keeps track of a list of plugin handlers. A plugin handler knows which plugin
library to load to get a specific class that is used to extend the
functionality of a specific base class and how to create an object
of this class. For example, to extend the base class TFile to be
able to read SQLite files one needs to load the plugin library
libRSQLite.so which defines the TRSQLiteServer class. This loading
should be triggered when a given URI contains a regular expression
defined by the handler.

Plugin handlers can be defined via macros in a list of plugin
directories. With $ROOTSYS/etc/plugins the default top plugin
directory specified in $ROOTSYS/etc/system.rootrc. Additional
directories can be specified by adding them to the end of the list.
Macros for identical plugin handlers in later directories will
override previous ones (the inverse of normal search path behavior).
The macros must have names like `<BaseClass>/PX0_<PluginClass>.C`,
e.g. TSQLServer/P20_TMySQLServer.C, to allow easy sorting and grouping.
If the BaseClass is in a namespace the directory must have the name
NameSpace@@BaseClass as `:` is a reserved pathname character on some
operating systems. Macros not beginning with 'P' and ending with ".C"
are ignored. These macros typically look like:
~~~ {.cpp}
  void P10_TDCacheFile()
  {
      gPluginMgr->AddHandler("TFile", "^dcache", "TDCacheFile",
         "DCache", "TDCacheFile(const char*,Option_t*)");
  }
~~~
Plugin handlers can also be defined via resources in the .rootrc
file. Although now deprecated this method still works for backward
compatibility, e.g.:
~~~ {.cpp}
  Plugin.TSQLServer:  ^mysql:  TMySQLServer MySQL  "<constructor>"
  +Plugin.TSQLServer: ^pgsql:  TPgSQLServer PgSQL  "<constructor>"
  Plugin.TVirtualFitter: *     TFitter      Minuit "TFitter(Int_t)"
~~~
Where the + in front of Plugin.TSQLServer says that it extends the
existing definition of TSQLServer, useful when there is more than
one plugin that can extend the same base class. The "<constructor>"
should be the constructor or a static method that generates an
instance of the specified class. Global methods should start with
"::" in their name, like "::CreateFitter()".
Instead of being a shared library a plugin can also be a CINT
script, so instead of libDialog.so one can have Dialog.C.
The * is a placeholder in case there is no need for a URI to
differentiate between different plugins for the same base class.
For the default plugins see $ROOTSYS/etc/system.rootrc.

Plugin handlers can also be registered at run time, e.g.:
~~~ {.cpp}
  gPluginMgr->AddHandler("TSQLServer", "^sqlite:",
                         "TSQLiteServer", "RSQLite",
            "TSQLiteServer(const char*,const char*,const char*)");
~~~
A list of currently defined handlers can be printed using:
~~~ {.cpp}
  gPluginMgr->Print(); // use option="a" to see ctors
~~~
The use of the plugin library manager removes all textual references
to hard-coded class and library names and the resulting dependencies
in the base classes. The plugin manager is used to extend a.o.
TFile, TSQLServer, TGrid, etc. functionality.
*/

#include "TPluginManager.h"
#include "Varargs.h"
#include "TEnv.h"
#include "TRegexp.h"
#include "TROOT.h"
#include "TSortedList.h"
#include "THashList.h"
#include "THashTable.h"
#include "Varargs.h"
#include "TClass.h"
#include "TInterpreter.h"
#include "TMethod.h"
#include "TMethodArg.h"
#include "TDataType.h"
#include "TMethodCall.h"
#include "TVirtualMutex.h"
#include "TSystem.h"
#include "TObjString.h"
#include "ThreadLocalStorage.h"

#include <memory>

TPluginManager *gPluginMgr;   // main plugin manager created in TROOT

static TVirtualMutex *gPluginManagerMutex;

static bool &TPH__IsReadingDirs() {
   TTHREAD_TLS(bool) readingDirs (false);
   return readingDirs;
}

ClassImp(TPluginHandler);

////////////////////////////////////////////////////////////////////////////////
/// Create a plugin handler. Called by TPluginManager.

TPluginHandler::TPluginHandler(const char *base, const char *regexp,
                               const char *className, const char *pluginName,
                               const char *ctor, const char *origin):
   fBase(base),
   fRegexp(regexp),
   fClass(className),
   fPlugin(pluginName),
   fCtor(ctor),
   fOrigin(origin),
   fCallEnv(0),
   fMethod(0),
   fCanCall(0),
   fIsMacro(kFALSE),
   fIsGlobal(kFALSE)
{
   TString aclicMode, arguments, io;
   TString fname = gSystem->SplitAclicMode(fPlugin, aclicMode, arguments, io);
   Bool_t validMacro = kFALSE;
   if (fname.EndsWith(".C") || fname.EndsWith(".cxx") || fname.EndsWith(".cpp") ||
       fname.EndsWith(".cc"))
      validMacro = kTRUE;

   if (validMacro && gROOT->LoadMacro(fPlugin, 0, kTRUE) == 0)
      fIsMacro = kTRUE;

   if (fCtor.BeginsWith("::")) {
      fIsGlobal = kTRUE;
      fCtor = fCtor.Strip(TString::kLeading, ':');
   }
}

////////////////////////////////////////////////////////////////////////////////
/// Cleanup plugin handler object.

TPluginHandler::~TPluginHandler()
{
   delete fCallEnv;
}

////////////////////////////////////////////////////////////////////////////////
/// Check if regular expression appears in the URI, if so return kTRUE.
/// If URI = 0 always return kTRUE.

Bool_t TPluginHandler::CanHandle(const char *base, const char *uri)
{
   if (fBase != base)
      return kFALSE;

   if (!uri || fRegexp == "*")
      return kTRUE;

   Bool_t wildcard = kFALSE;
   if (!fRegexp.MaybeRegexp())
      wildcard = kTRUE;

   TRegexp re(fRegexp, wildcard);
   TString ruri = uri;

   if (ruri.Index(re) != kNPOS)
      return kTRUE;
   return kFALSE;
}

////////////////////////////////////////////////////////////////////////////////
/// Setup ctor or static method call environment.

void TPluginHandler::SetupCallEnv()
{
   int setCanCall = -1;

   // Use a exit_scope guard, to insure that fCanCall is set (to the value of
   // result) as the last action of this function before returning.

   // When the standard supports it, we should use std::exit_code
   // See N4189 for example.
   //    auto guard = make_exit_scope( [...]() { ... } );
   using exit_scope = std::shared_ptr<void*>;
   exit_scope guard(nullptr,
                    [this,&setCanCall](void *) { this->fCanCall = setCanCall; } );

   // check if class exists
   TClass *cl = TClass::GetClass(fClass);
   if (!cl && !fIsGlobal) {
      Error("SetupCallEnv", "class %s not found in plugin %s", fClass.Data(),
            fPlugin.Data());
      return;
   }

   // split method and prototype strings
   TString method = fCtor(0, fCtor.Index("("));
   TString proto  = fCtor(fCtor.Index("(")+1, fCtor.Index(")")-fCtor.Index("(")-1);

   if (fIsGlobal) {
      cl = 0;
      fMethod = gROOT->GetGlobalFunctionWithPrototype(method, proto, kFALSE);
   } else {
      fMethod = cl->GetMethodWithPrototype(method, proto);
   }

   if (!fMethod) {
      if (fIsGlobal)
         Error("SetupCallEnv", "global function %s not found", method.Data());
      else
         Error("SetupCallEnv", "method %s not found in class %s", method.Data(),
               fClass.Data());
      return;
   }

   if (!fIsGlobal && !(fMethod->Property() & kIsPublic)) {
      Error("SetupCallEnv", "method %s is not public", method.Data());
      return;
   }

   fCallEnv = new TMethodCall;
   fCallEnv->Init(fMethod);

   setCanCall = 1;

   return;
}

////////////////////////////////////////////////////////////////////////////////
/// Check if the plugin library for this handler exits. Returns 0
/// when it exists and -1 in case the plugin does not exist.

Int_t TPluginHandler::CheckPlugin() const
{
   if (fIsMacro) {
      if (TClass::GetClass(fClass)) return 0;
      return gROOT->LoadMacro(fPlugin, 0, kTRUE);
   } else
      return gROOT->LoadClass(fClass, fPlugin, kTRUE);
}

////////////////////////////////////////////////////////////////////////////////
/// Load the plugin library for this handler. Returns 0 on successful loading
/// and -1 in case the library does not exist or in case of error.

Int_t TPluginHandler::LoadPlugin()
{
   if (fIsMacro) {
      if (TClass::GetClass(fClass)) return 0;
      return gROOT->LoadMacro(fPlugin);
   } else {
      // first call also loads dependent libraries declared via the rootmap file
      if (TClass::LoadClass(fClass, /* silent = */ kFALSE)) return 0;
      return gROOT->LoadClass(fClass, fPlugin);
   }
}

////////////////////////////////////////////////////////////////////////////////
/// Check that we can properly run ExecPlugin.

Bool_t TPluginHandler::CheckForExecPlugin(Int_t nargs)
{
   if (fCtor.IsNull()) {
      Error("ExecPlugin", "no ctor specified for this handler %s", fClass.Data());
      return kFALSE;
   }

   if (fCanCall == 0) {
      // Not initialized yet.
      // SetupCallEnv is likely to require/take the interpreter lock.
      // Grab it now to avoid dead-lock.  In particular TPluginHandler::ExecPluginImpl
      // takes the gInterpreterMutex and *then* call (indirectly) code that
      // take the gPluginManagerMutex.
      R__LOCKGUARD(gInterpreterMutex);
      R__LOCKGUARD2(gPluginManagerMutex);

      // Now check if another thread did not already do the work.
      if (fCanCall == 0)
         SetupCallEnv();
   }

   if (fCanCall == -1)
      return kFALSE;

   if (nargs < fMethod->GetNargs() - fMethod->GetNargsOpt() ||
       nargs > fMethod->GetNargs()) {
      Error("ExecPlugin", "nargs (%d) not consistent with expected number of arguments ([%d-%d])",
            nargs, fMethod->GetNargs() - fMethod->GetNargsOpt(),
            fMethod->GetNargs());
      return kFALSE;
   }

   return kTRUE;
}

////////////////////////////////////////////////////////////////////////////////
/// Print info about the plugin handler. If option is "a" print
/// also the ctor's that will be used.

void TPluginHandler::Print(Option_t *opt) const
{
   const char *exist = "";
   if (CheckPlugin() == -1)
      exist = " [*]";

   Printf("%-20s %-13s %-18s %s%s", fBase.Data(), fRegexp.Data(),
          fClass.Data(), fPlugin.Data(), exist);
   if (strchr(opt, 'a')) {
      if (!exist[0]) {
         TString lib = fPlugin;
         if (!lib.BeginsWith("lib"))
            lib = "lib" + lib;
         char *path = gSystem->DynamicPathName(lib, kTRUE);
         if (path) Printf("  [Lib:  %s]", path);
         delete [] path;
      }
      Printf("  [Ctor: %s]", fCtor.Data());
      Printf("  [origin: %s]", fOrigin.Data());
   }
}


ClassImp(TPluginManager);

////////////////////////////////////////////////////////////////////////////////
/// Clean up the plugin manager.

TPluginManager::~TPluginManager()
{
   delete fHandlers;
   delete fBasesLoaded;
}

////////////////////////////////////////////////////////////////////////////////
/// Load plugin handlers specified in config file, like:
/// ~~~ {.cpp}
///    Plugin.TSQLServer:  ^mysql:   TMySQLServer   MySQL "TMySQLServer(...)"
///    +Plugin.TSQLServer: ^pgsql:   TPgSQLServer   PgSQL "TPgSQLServer(...)"
/// ~~~
/// The + allows the extension of an already defined resource (see TEnv).

void TPluginManager::LoadHandlersFromEnv(TEnv *env)
{
   if (!env) return;

   TIter next(env->GetTable());
   TEnvRec *er;

   while ((er = (TEnvRec*) next())) {
      const char *s;
      if ((s = strstr(er->GetName(), "Plugin."))) {
         // use s, i.e. skip possible OS and application prefix to Plugin.
         // so that GetValue() takes properly care of returning the value
         // for the specified OS and/or application
         const char *val = env->GetValue(s, (const char*)0);
         if (val) {
            Int_t cnt = 0;
            char *v = StrDup(val);
            s += 7;
            while (1) {
               TString regexp = strtok(!cnt ? v : 0, "; "); // this method does not need to be reentrant
               if (regexp.IsNull()) break;
               TString clss   = strtok(0, "; ");
               if (clss.IsNull()) break;
               TString plugin = strtok(0, "; ");
               if (plugin.IsNull()) break;
               TString ctor = strtok(0, ";\"");
               if (!ctor.Contains("("))
                  ctor = strtok(0, ";\"");
               AddHandler(s, regexp, clss, plugin, ctor, "TEnv");
               cnt++;
            }
            delete [] v;
         }
      }
   }
}

////////////////////////////////////////////////////////////////////////////////
/// Load all plugin macros from the specified path/base directory.

void TPluginManager::LoadHandlerMacros(const char *path)
{
   void *dirp = gSystem->OpenDirectory(path);
   if (dirp) {
      if (gDebug > 0)
         Info("LoadHandlerMacros", "%s", path);
      TSortedList macros;
      macros.SetOwner();
      const char *f1;
      while ((f1 = gSystem->GetDirEntry(dirp))) {
         TString f = f1;
         if (f[0] == 'P' && f.EndsWith(".C")) {
            const char *p = gSystem->ConcatFileName(path, f);
            if (!gSystem->AccessPathName(p, kReadPermission)) {
               macros.Add(new TObjString(p));
            }
            delete [] p;
         }
      }
      // load macros in alphabetical order
      TIter next(&macros);
      TObjString *s;
      while ((s = (TObjString*)next())) {
         if (gDebug > 1)
            Info("LoadHandlerMacros", "   plugin macro: %s", s->String().Data());
         Long_t res;
         if ((res = gROOT->Macro(s->String(), 0, kFALSE)) < 0) {
            Error("LoadHandlerMacros", "pluging macro %s returned %ld",
                  s->String().Data(), res);
         }
      }
   }
   gSystem->FreeDirectory(dirp);
}

////////////////////////////////////////////////////////////////////////////////
/// Load plugin handlers specified via macros in a list of plugin
/// directories. The `$ROOTSYS/etc/plugins` is the default top plugin directory
/// specified in `$ROOTSYS/etc/system.rootrc`. The macros must have names
/// like `<BaseClass>/PX0_<PluginClass>.C`, e.g. //`TSQLServer/P20_TMySQLServer.C`,
/// to allow easy sorting and grouping. If the BaseClass is in a namespace
/// the directory must have the name NameSpace@@BaseClass as : is a reserved
/// pathname character on some operating systems. Macros not beginning with
/// 'P' and ending with ".C" are ignored. If base is specified only plugin
/// macros for that base class are loaded. The macros typically
/// should look like:
/// ~~~ {.cpp}
///   void P10_TDCacheFile()
///   {
///       gPluginMgr->AddHandler("TFile", "^dcache", "TDCacheFile",
///          "DCache", "TDCacheFile(const char*,Option_t*,const char*,Int_t)");
///   }
/// ~~~
/// In general these macros should not cause side effects, by changing global
/// ROOT state via, e.g. gSystem calls, etc. However, in specific cases
/// this might be useful, e.g. adding a library search path, adding a specific
/// dependency, check on some OS or ROOT capability or downloading
/// of the plugin.

void TPluginManager::LoadHandlersFromPluginDirs(const char *base)
{
   TString sbase = base;
   if (sbase.Length())
      sbase.ReplaceAll("::", "@@");

   R__READ_LOCKGUARD(ROOT::gCoreMutex);

   if (fBasesLoaded && fBasesLoaded->FindObject(sbase))
      return;

   R__WRITE_LOCKGUARD(ROOT::gCoreMutex);

   // While waiting for the lock, another thread may
   // have process the requested plugin.
   if (fBasesLoaded && fBasesLoaded->FindObject(sbase))
      return;

   if (!fBasesLoaded) {
      fBasesLoaded = new THashTable();
      fBasesLoaded->SetOwner();
   }
   fBasesLoaded->Add(new TObjString(sbase));

   TPH__IsReadingDirs() = kTRUE;

   TString plugindirs = gEnv->GetValue("Root.PluginPath", (char*)0);
   if (plugindirs.Length() == 0) {
      plugindirs = "plugins";
      gSystem->PrependPathName(TROOT::GetEtcDir(), plugindirs);
   }
#ifdef WIN32
   TObjArray *dirs = plugindirs.Tokenize(";");
#else
   TObjArray *dirs = plugindirs.Tokenize(":");
#endif
   TString d;
   for (Int_t i = 0; i < dirs->GetEntriesFast(); i++) {
      d = ((TObjString*)dirs->At(i))->GetString();
      // check if directory already scanned
      Int_t skip = 0;
      for (Int_t j = 0; j < i; j++) {
         TString pd = ((TObjString*)dirs->At(j))->GetString();
         if (pd == d) {
            skip++;
            break;
         }
      }
      if (!skip) {
         if (sbase != "") {
            const char *p = gSystem->ConcatFileName(d, sbase);
            LoadHandlerMacros(p);
            delete [] p;
         } else {
            void *dirp = gSystem->OpenDirectory(d);
            if (dirp) {
               if (gDebug > 0)
                  Info("LoadHandlersFromPluginDirs", "%s", d.Data());
               const char *f1;
               while ((f1 = gSystem->GetDirEntry(dirp))) {
                  TString f = f1;
                  const char *p = gSystem->ConcatFileName(d, f);
                  LoadHandlerMacros(p);
                  fBasesLoaded->Add(new TObjString(f));
                  delete [] p;
               }
            }
            gSystem->FreeDirectory(dirp);
         }
      }
   }
   TPH__IsReadingDirs() = kFALSE;
   delete dirs;
}

////////////////////////////////////////////////////////////////////////////////
/// Add plugin handler to the list of handlers. If there is already a
/// handler defined for the same base and regexp it will be replaced.

void TPluginManager::AddHandler(const char *base, const char *regexp,
                                const char *className, const char *pluginName,
                                const char *ctor, const char *origin)
{
   {
      R__LOCKGUARD2(gPluginManagerMutex);
      if (!fHandlers) {
         fHandlers = new TList;
         fHandlers->SetOwner();
      }
   }
   // make sure there is no previous handler for the same case
   RemoveHandler(base, regexp);

   if (TPH__IsReadingDirs())
      origin = gInterpreter->GetCurrentMacroName();

   TPluginHandler *h = new TPluginHandler(base, regexp, className,
                                          pluginName, ctor, origin);
   {
      R__LOCKGUARD2(gPluginManagerMutex);
      fHandlers->Add(h);
   }
}

////////////////////////////////////////////////////////////////////////////////
/// Remove handler for the specified base class and the specified
/// regexp. If regexp=0 remove all handlers for the specified base.

void TPluginManager::RemoveHandler(const char *base, const char *regexp)
{
   R__LOCKGUARD2(gPluginManagerMutex);
   if (!fHandlers) return;

   TIter next(fHandlers);
   TPluginHandler *h;

   while ((h = (TPluginHandler*) next())) {
      if (h->fBase == base) {
         if (!regexp || h->fRegexp == regexp) {
            fHandlers->Remove(h);
            delete h;
         }
      }
   }
}

////////////////////////////////////////////////////////////////////////////////
/// Returns the handler if there exists a handler for the specified URI.
/// The uri can be 0 in which case the first matching plugin handler
/// will be returned. Returns 0 in case handler is not found.

TPluginHandler *TPluginManager::FindHandler(const char *base, const char *uri)
{
   LoadHandlersFromPluginDirs(base);

   R__LOCKGUARD2(gPluginManagerMutex);
   TIter next(fHandlers);
   TPluginHandler *h;

   while ((h = (TPluginHandler*) next())) {
      if (h->CanHandle(base, uri)) {
         if (gDebug > 0)
            Info("FindHandler", "found plugin for %s", h->GetClass());
         return h;
      }
   }

   if (gDebug > 2) {
      if (uri)
         Info("FindHandler", "did not find plugin for class %s and uri %s", base, uri);
      else
         Info("FindHandler", "did not find plugin for class %s", base);
   }

   return 0;
}

////////////////////////////////////////////////////////////////////////////////
/// Print list of registered plugin handlers. If option is "a" print
/// also the ctor's that will be used.

void TPluginManager::Print(Option_t *opt) const
{
   if (!fHandlers) return;

   TIter next(fHandlers);
   TPluginHandler *h;
   Int_t cnt = 0, cntmiss = 0;

   Printf("=====================================================================");
   Printf("Base                 Regexp        Class              Plugin");
   Printf("=====================================================================");

   while ((h = (TPluginHandler*) next())) {
      cnt++;
      h->Print(opt);
      if (h->CheckPlugin() == -1)
         cntmiss++;
   }
   Printf("=====================================================================");
   Printf("%d plugin handlers registered", cnt);
   Printf("[*] %d %s not available", cntmiss, cntmiss==1 ? "plugin" : "plugins");
   Printf("=====================================================================\n");
}

////////////////////////////////////////////////////////////////////////////////
/// Write in the specified directory the plugin macros. If plugin is specified
/// and if it is a base class all macros for that base will be written. If it
/// is a plugin class name, only that one macro will be written. If plugin
/// is 0 all macros are written. Returns -1 if dir does not exist, 0 otherwise.

Int_t TPluginManager::WritePluginMacros(const char *dir, const char *plugin) const
{
   const_cast<TPluginManager*>(this)->LoadHandlersFromPluginDirs();

   if (!fHandlers) return 0;

   TString d;
   if (!dir || !dir[0])
      d = ".";
   else
      d = dir;

   if (gSystem->AccessPathName(d, kWritePermission)) {
      Error("WritePluginMacros", "cannot write in directory %s", d.Data());
      return -1;
   }

   TString base;
   Int_t   idx = 0;

   TObjLink *lnk = fHandlers->FirstLink();
   while (lnk) {
      TPluginHandler *h = (TPluginHandler *) lnk->GetObject();
      if (plugin && strcmp(plugin, h->fBase) && strcmp(plugin, h->fClass)) {
         lnk = lnk->Next();
         continue;
      }
      if (base != h->fBase) {
         idx = 10;
         base = h->fBase;
      } else
         idx += 10;
      const char *dd = gSystem->ConcatFileName(d, h->fBase);
      TString sdd = dd;
      sdd.ReplaceAll("::", "@@");
      delete [] dd;
      if (gSystem->AccessPathName(sdd, kWritePermission)) {
         if (gSystem->MakeDirectory(sdd) < 0) {
            Error("WritePluginMacros", "cannot create directory %s", sdd.Data());
            return -1;
         }
      }
      TString fn;
      fn.Form("P%03d_%s.C", idx, h->fClass.Data());
      const char *fd = gSystem->ConcatFileName(sdd, fn);
      FILE *f = fopen(fd, "w");
      if (f) {
         fprintf(f, "void P%03d_%s()\n{\n", idx, h->fClass.Data());
         fprintf(f, "   gPluginMgr->AddHandler(\"%s\", \"%s\", \"%s\",\n",
                 h->fBase.Data(), h->fRegexp.Data(), h->fClass.Data());
         fprintf(f, "      \"%s\", \"%s\");\n", h->fPlugin.Data(), h->fCtor.Data());

         // check for different regexps cases for the same base + class and
         // put them all in the same macro
         TObjLink *lnk2 = lnk->Next();
         while (lnk2) {
            TPluginHandler *h2 = (TPluginHandler *) lnk2->GetObject();
            if (h->fBase != h2->fBase || h->fClass != h2->fClass)
               break;

            fprintf(f, "   gPluginMgr->AddHandler(\"%s\", \"%s\", \"%s\",\n",
                    h2->fBase.Data(), h2->fRegexp.Data(), h2->fClass.Data());
            fprintf(f, "      \"%s\", \"%s\");\n", h2->fPlugin.Data(), h2->fCtor.Data());

            lnk  = lnk2;
            lnk2 = lnk2->Next();
         }
         fprintf(f, "}\n");
         fclose(f);
      }
      delete [] fd;
      lnk = lnk->Next();
   }
   return 0;
}

////////////////////////////////////////////////////////////////////////////////
/// Write in the specified environment config file the plugin records. If
/// plugin is specified and if it is a base class all records for that
/// base will be written. If it is a plugin class name, only that one
/// record will be written. If plugin is 0 all macros are written.
/// If envFile is 0 or "" the records are written to stdout.
/// Returns -1 if envFile cannot be created or opened, 0 otherwise.

Int_t TPluginManager::WritePluginRecords(const char *envFile, const char *plugin) const
{
   const_cast<TPluginManager*>(this)->LoadHandlersFromPluginDirs();

   if (!fHandlers) return 0;

   FILE *fd;
   if (!envFile || !envFile[0])
      fd = stdout;
   else
      fd = fopen(envFile, "w+");

   if (!fd) {
      Error("WritePluginRecords", "error opening file %s", envFile);
      return -1;
   }

   TString base, base2;
   Int_t   idx = 0;

   TObjLink *lnk = fHandlers->FirstLink();
   while (lnk) {
      TPluginHandler *h = (TPluginHandler *) lnk->GetObject();
      if (plugin && strcmp(plugin, h->fBase) && strcmp(plugin, h->fClass)) {
         lnk = lnk->Next();
         continue;
      }
      if (base != h->fBase) {
         idx = 1;
         base = h->fBase;
         base2 = base;
         base2.ReplaceAll("::", "@@");
      } else
         idx += 1;

      if (idx == 1)
         fprintf(fd, "Plugin.%s: %s %s %s \"%s\"\n", base2.Data(), h->fRegexp.Data(),
                 h->fClass.Data(), h->fPlugin.Data(), h->fCtor.Data());
      else
         fprintf(fd, "+Plugin.%s: %s %s %s \"%s\"\n", base2.Data(), h->fRegexp.Data(),
                 h->fClass.Data(), h->fPlugin.Data(), h->fCtor.Data());

      // check for different regexps cases for the same base + class and
      // put them all in the same macro
      TObjLink *lnk2 = lnk->Next();
      while (lnk2) {
         TPluginHandler *h2 = (TPluginHandler *) lnk2->GetObject();
         if (h->fBase != h2->fBase || h->fClass != h2->fClass)
            break;

         fprintf(fd, "+Plugin.%s: %s %s %s \"%s\"\n", base2.Data(), h2->fRegexp.Data(),
                 h2->fClass.Data(), h2->fPlugin.Data(), h2->fCtor.Data());

         lnk  = lnk2;
         lnk2 = lnk2->Next();
      }
      lnk = lnk->Next();
   }

   if (envFile && envFile[0])
      fclose(fd);

   return 0;
}