Bugfix: Temporary time zone switching not working correctly

- On Linux/glibc, must call tzset() explicitly to pick up change of TZ. - On macOS (possibly elsewhere), must save the return value from getenv(); the pointed-to string may change if the environment is updated. - Must check if time zone correction is needed at actual run date/time
JeffersonLab · Nov 29, 2023 · 5188881 · 5188881
1 parent c00260d
commit 5188881
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Showing 3 changed files with 77 additions and 52 deletions.
diff --git a/Database/Database.cxx b/Database/Database.cxx
@@ -78,52 +78,6 @@ const char* Here( const char* method, const char* prefix )
 //=============================================================================
 namespace Podd {
 
-namespace {
-
-const char* gDefaultTZString = "US/Eastern";
-
-//_____________________________________________________________________________
-Long64_t GetOffsetToLocal(const char* tz)
-{
-  // Returns the offset in seconds between the given time zone 'tz' and
-  // the time zone of the local machine
-  time_t tloc = time(nullptr);
-  struct tm tml{}, tmd{};
-  localtime_r(&tloc, &tml);
-
-  const char* cur_tz = gSystem->Getenv("TZ");
-  gSystem->Setenv("TZ", tz);
-  localtime_r(&tloc, &tmd);
-  if( cur_tz )
-    gSystem->Setenv("TZ", cur_tz);
-  else
-    gSystem->Unsetenv("TZ");
-
-  return tmd.tm_gmtoff - tml.tm_gmtoff;
-}
-
-//_____________________________________________________________________________
-TString MkDefaultTZ()
-{
-  gNeedTZCorrection = (GetOffsetToLocal(gDefaultTZString) != 0);
-  return gDefaultTZString;
-}
-
-} // namespace
-
-TString gDefaultTZ = MkDefaultTZ();
-Bool_t  gNeedTZCorrection = true;
-
-//_____________________________________________________________________________
-void SetDefaultTZ( const char* tz )
-{
-  if( !tz || !*tz ) {
-    tz = gDefaultTZString;
-  }
-  gNeedTZCorrection = (GetOffsetToLocal(tz) != 0);
-  gDefaultTZ = tz;
-}
-
 //_____________________________________________________________________________
 TString& GetObjArrayString( const TObjArray* array, Int_t i )
 {
@@ -1385,6 +1339,52 @@ Bool_t IsDBtimestamp( const string& line, TDatime& date )
   return IsDBdate(line, ldate, true);
 }
 
+//_____________________________________________________________________________
+// Timezone handling
+const char* const gDefaultTZString = "US/Eastern";
+
+TString gDefaultTZ = gDefaultTZString;
+Bool_t  gNeedTZCorrection = true;
+
+//_____________________________________________________________________________
+// Set time zone to assume for legacy database time stamps without time zone
+// offsets. The default is "US/Eastern".
+void SetDefaultTZ( const char* tz )
+{
+  if( !tz || !*tz ) {
+    tz = gDefaultTZString;
+  }
+  gDefaultTZ = tz;
+}
+
+//_____________________________________________________________________________
+// Helper function for time zone calculations. Determine offset between
+// the default time zone and the local time zone at Unix time 'tloc'.
+Long64_t GetTZOffsetToLocal( UInt_t tloc )
+{
+  // Returns the offset in seconds between the given time zone 'tz' and
+  // the time zone of the local machine
+  auto timet = static_cast<time_t>(tloc);
+  struct tm tml{}, tmd{};
+  localtime_r(&timet, &tml);
+
+  TString cur_tz = gSystem->Getenv("TZ");
+  gSystem->Setenv("TZ", gDefaultTZ);
+#ifdef __GLIBC__
+  tzset();
+#endif
+  localtime_r(&timet, &tmd);
+  if( !cur_tz.IsNull() )
+    gSystem->Setenv("TZ", cur_tz);
+  else
+    gSystem->Unsetenv("TZ");
+
+#ifdef __GLIBC__
+  tzset();
+#endif
+  return tmd.tm_gmtoff - tml.tm_gmtoff;
+}
+
 //_____________________________________________________________________________
 #ifdef __clang__
 // Clang appears to make implicitly instantiated template functions private

diff --git a/Database/Database.h b/Database/Database.h
@@ -17,10 +17,9 @@
 // For backward compatibility with existing client code
 #include "Textvars.h"
 #include "TDatime.h"
+#include "TString.h"
 
 class TObjArray;
-//class TDatime;
-class TString;
 
 // Helper function for error messages
 const char* Here( const char* here, const char* prefix = nullptr );
@@ -66,24 +65,46 @@ Bool_t   IsDBtimestamp( const std::string& line, TDatime& keydate );
 
 // Time zone to assume for legacy database time stamps without time zone offsets.
 // The default is "US/Eastern".
-void     SetDefaultTZ(const char* tz = nullptr);
+void     SetDefaultTZ( const char* tz = nullptr );
+Long64_t GetTZOffsetToLocal( UInt_t tloc );
 extern TString  gDefaultTZ;
 extern Bool_t   gNeedTZCorrection;
 
 }  // namespace Podd
 
+// Macro for running arbitrary code ("cmd") with TZ set to gDefaultTZ.
+#ifdef __GLIBC__
+// glibc seems to require an explicit call to tzset() to pick up a change of TZ
+#include <ctime>
 #define WithDefaultTZ(cmd)                   \
- const char* cur_tz = nullptr;               \
+ TString cur_tz;                             \
  if( Podd::gNeedTZCorrection ) {             \
    cur_tz = gSystem->Getenv("TZ");           \
    gSystem->Setenv("TZ", Podd::gDefaultTZ);  \
+   tzset();                                  \
  }                                           \
  cmd;                                        \
  if( Podd::gNeedTZCorrection ) {             \
-   if( cur_tz )                              \
+   if( !cur_tz.IsNull() )                    \
      gSystem->Setenv("TZ", cur_tz );         \
    else                                      \
      gSystem->Unsetenv("TZ");                \
+   tzset();                                  \
  }
+#else
+#define WithDefaultTZ(cmd)                   \
+ TString cur_tz;                             \
+ if( Podd::gNeedTZCorrection ) {             \
+   cur_tz = gSystem->Getenv("TZ");           \
+   gSystem->Setenv("TZ", Podd::gDefaultTZ);  \
+ }                                           \
+ cmd;                                        \
+ if( Podd::gNeedTZCorrection ) {             \
+   if( !cur_tz.IsNull() )                    \
+     gSystem->Setenv("TZ", cur_tz );         \
+   else                                      \
+     gSystem->Unsetenv("TZ");                \
+ }
+#endif
 
 #endif //Podd_Database_h_
diff --git a/Podd/THaRunBase.cxx b/Podd/THaRunBase.cxx
@@ -22,6 +22,7 @@
 #include <iterator>   // std::begin, std::end
 
 using namespace std;
+using namespace Podd;
 
 static const int UNDEFDATE = 19950101;
 static const char* NOTINIT = "uninitialized run";
@@ -144,7 +145,9 @@ Int_t THaRunBase::Update( const THaEvData* evdata )
   if( evdata->IsPrestartEvent() ) {
     fDataRead |= kDate|kRunNumber|kRunType;
     if( !fAssumeDate ) {
-      WithDefaultTZ(fDate.Set( evdata->GetRunTime() ));
+      UInt_t tloc = evdata->GetRunTime();
+      gNeedTZCorrection = (GetTZOffsetToLocal(tloc) != 0);
+      WithDefaultTZ(fDate.Set(tloc));
       fDataSet |= kDate;
     }
     SetNumber( evdata->GetRunNum() );
@@ -512,6 +515,7 @@ void THaRunBase::SetDate( UInt_t tloc )
   // Set timestamp of this run to 'tloc' which is in Unix time
   // format (number of seconds since 01 Jan 1970).
 
+  gNeedTZCorrection = (GetTZOffsetToLocal(tloc) != 0);
   WithDefaultTZ(TDatime date( tloc ));
   SetDate( date );
 }