Update to allow Alignment to run multithreaded

Modifications to allow running multithreaded:

• rewrote AlElementHistos to use Accumulator::Histogram
• changed from mutex to shared_mutex to profit from readonly locks
• create AlEquations object in each event call on the stack and add at end of event to minimize number of write locks
• AlignAlgorithm no longer derives from GaudiHistoAlg
• update gaudiiter to support running multi-threaded (works on MDF files only)

This addresses most of what is discussed in #30

This also fixes a crash in a test on clang that was due to a bug in the IO of the Al::Equations object.

@graven, @jcobbled

Alignment/TAlignment/include/TAlignment/AlElementHistos.h

@@ -12,31 +12,72 @@
 
 #include <cstddef>
 
-namespace AIDA {
-  class IHistogram1D;
-  class IHistogram2D;
-} // namespace AIDA
+#include "Gaudi/Accumulators/Histogram.h"
+#include "TAlignment/AlignmentElement.h"
 
-struct GaudiHistoAlg;
+// FIXME: temporarily disable a non-understood warning on gcc11
+#ifndef __clang__
+#  pragma GCC diagnostic ignored "-Wsubobject-linkage"
+#endif
 
 namespace LHCb::Alignment {
-  class Element;
 
   struct AlElementHistos {
-    AlElementHistos( GaudiHistoAlg& parent, const Alignment::Element& elem, std::size_t niter );
-    void                reset();
-    AIDA::IHistogram2D* m_resHisto;
-    AIDA::IHistogram2D* m_unbiasedResHisto;
-    AIDA::IHistogram2D* m_pullHisto;
-    AIDA::IHistogram1D* m_nHitsHisto;
-    //   AIDA::IHistogram1D* m_deltaTxHisto;
-    //   AIDA::IHistogram1D* m_deltaTyHisto;
-    //   AIDA::IHistogram1D* m_deltaTzHisto;
-    //   AIDA::IHistogram1D* m_deltaRxHisto;
-    //   AIDA::IHistogram1D* m_deltaRyHisto;
-    //   AIDA::IHistogram1D* m_deltaRzHisto;
-    AIDA::IHistogram2D* m_autoCorrHisto;
-    AIDA::IHistogram1D* m_residualPullHistos[6];
+    using Histogram2D = Gaudi::Accumulators::Histogram<2>;
+    using Histogram1D = Gaudi::Accumulators::Histogram<1>;
+
+    std::string m_name;
+    size_t      m_index;
+    std::string m_dir;
+    double      m_resmax;
+    Histogram2D m_resHisto;
+    Histogram2D m_unbiasedResHisto;
+    Histogram2D m_pullHisto;
+    Histogram1D m_nHitsHisto;
+    Histogram2D m_autoCorrHisto;
+    Histogram1D m_residualPullHistos[6];
+
+    template <typename OWNER>
+    AlElementHistos( const OWNER* owner, const Alignment::Element& elem, unsigned int numiter )
+        : m_name{elem.name()}
+        , m_index{elem.index()}
+        , m_dir{"element" + std::to_string( elem.index() ) + "/"}
+        , m_resmax{elem.histoResidualMax()}
+        , m_resHisto{owner,
+                     m_dir + std::to_string( 1000u ),
+                     "Residual vs iteration for " + m_name,
+                     {numiter, -0.5, numiter - 0.5},
+                     {100, -m_resmax, +m_resmax}}
+        , m_unbiasedResHisto{owner,
+                             m_dir + std::to_string( 1001u ),
+                             "Unbiased Residual vs iteration for " + m_name,
+                             {numiter, -0.5, numiter - 0.5},
+                             {100, -m_resmax, +m_resmax}}
+        , m_pullHisto{owner,
+                      m_dir + std::to_string( 2000u ),
+                      "Pull vs iteration for " + m_name,
+                      {numiter, -0.5, numiter - 0.5},
+                      {100, -5.0, 5.0}}
+        , m_nHitsHisto{owner,
+                       m_dir + std::to_string( 3000u ),
+                       "Number of hits vs iteration for " + m_name,
+                       {numiter, -0.5, numiter - 0.5}}
+        , m_autoCorrHisto{owner,
+                          m_dir + std::to_string( 4000u ),
+                          "hit residual scale factor in " + m_name + "  vs iteration ",
+                          {numiter, -0.5, numiter - 0.5},
+                          {100, -1, 1}}
+        , m_residualPullHistos{{owner, m_dir + "ResPullTx", "Residual pull Tx", {50, -5.0, 5.0}},
+                               {owner, m_dir + "ResPullTy", "Residual pull Ty", {50, -5.0, 5.0}},
+                               {owner, m_dir + "ResPullTz", "Residual pull Tz", {50, -5.0, 5.0}},
+                               {owner, m_dir + "ResPullRx", "Residual pull Rx", {50, -5.0, 5.0}},
+                               {owner, m_dir + "ResPullRy", "Residual pull Ry", {50, -5.0, 5.0}},
+                               {owner, m_dir + "ResPullRz", "Residual pull Rz", {50, -5.0, 5.0}}} {}
+
+    void reset() {
+      // only reset histograms that don't go by 'iteration'
+      for ( size_t ipar = 0; ipar < 6; ++ipar ) m_residualPullHistos[ipar].reset();
+    }
   };
 
 } // namespace LHCb::Alignment