[io] use UUIDv4 in TFile unconditionally

Author: jblomer

core/base/inc/TDirectory.h

@@ -140,7 +140,7 @@ can be replaced with the simpler and exception safe:
 
    TObject         *fMother{nullptr};   ///< pointer to mother of the directory
    TList           *fList{nullptr};     ///< List of objects in memory
-   TUUID            fUUID;              ///< Unique identifier
+   TUUID            fUUID{TUUID::UUIDv4()}; ///< Unique identifier
    mutable TString  fPathBuffer;        ///<! Buffer for GetPath() function
    TContext        *fContext{nullptr};  ///<! Pointer to a list of TContext object pointing to this TDirectory
 

core/base/src/TDirectory.cxx

@@ -52,10 +52,6 @@ Describe directory structure in memory.
 
 TDirectory::TDirectory() : TNamed()
 {
-   // In the context of rootcling, we don't have gSystem
-   if (gSystem)
-      fUUID = TUUID::UUIDv4();
-
    // MSVC doesn't support fSpinLock=ATOMIC_FLAG_INIT; in the class definition
    std::atomic_flag_clear( &fSpinLock );
 }
@@ -76,10 +72,6 @@ TDirectory::TDirectory() : TNamed()
 TDirectory::TDirectory(const char *name, const char *title, Option_t * /*classname*/, TDirectory* initMotherDir)
    : TNamed(name, title)
 {
-   // In the context of rootcling, we don't have gSystem
-   if (gSystem)
-      fUUID = TUUID::UUIDv4();
-
    // MSVC doesn't support fSpinLock=ATOMIC_FLAG_INIT; in the class definition
    std::atomic_flag_clear( &fSpinLock );
 

core/base/src/TUUID.cxx

@@ -113,6 +113,8 @@ system clock tick, the UUID generator will stall until the
 system clock catches up.
 */
 
+#include <ROOT/RCryptoRandom.hxx>
+
 #include "TROOT.h"
 #include "TDatime.h"
 #include "TUUID.h"
@@ -165,9 +167,8 @@ TUUID::TUUID(TV4Marker)
    // Ensure we can treat the memory starting at uuid.fTimeLow as an array of 16 octets
    assert(&fNode[5] - reinterpret_cast<unsigned char *>(&fTimeLow) + 1 == 16);
 
-   R__ASSERT(gSystem);
-   const auto rv = gSystem->GetCryptoRandom(&fTimeLow, 16);
-   R__ASSERT(rv == 16);
+   const auto rv = ROOT::Internal::GetCryptoRandom(&fTimeLow, 16);
+   R__ASSERT(rv);
    // Fix up variant
    fClockSeqHiAndReserved = (fClockSeqHiAndReserved & 0x3F) | (2 << 6);
    // Fix up version