Don't open the history file for enery entered line, to determine its number of lines.

Do it when we reach 50% of the difference between fPruneLength and fMaxDepth: this means the history file can contain more lines than fMaxDepth (if multiple processes write to it sort of synchronously), but not many (getting them to work synchronously over hundreds of lines is rare).


git-svn-id: http://root.cern.ch/svn/root/trunk@39533 27541ba8-7e3a-0410-8455-c3a389f83636

core/textinput/src/textinput/History.cpp

@@ -25,7 +25,7 @@
 namespace textinput {
   History::History(const char* filename):
     fHistFileName(filename ? filename : ""), fMaxDepth((size_t) -1),
-    fPruneLength(0) {
+    fPruneLength(0), fNumHistFileLines(0) {
     // Create a history object, initialize from filename if the file
     // exists. Append new lines to filename taking into account the
     // maximal number of lines allowed by SetMaxDepth().
@@ -37,6 +37,7 @@ namespace textinput {
   void
   History::AddLine(const std::string& line) {
     // Add a line to entries and file.
+    if (line.empty()) return;
     fEntries.push_back(line);
     AppendToFile();
   }
@@ -55,8 +56,11 @@ namespace textinput {
         if (c != '\n' && c != '\r') break;
         line.erase(len - 1);
       }
-      fEntries.push_back(line);
+      if (!line.empty()) {
+        fEntries.push_back(line);
+      }
     }
+    fNumHistFileLines = fEntries.size();
   }
 
   void
@@ -65,23 +69,32 @@ namespace textinput {
     // Prune if needed.
     if (fHistFileName.empty() || !fMaxDepth) return;
 
-    // Count lines:
-    size_t numLines = 0;
-    std::string line;
-    std::ifstream in(fHistFileName.c_str());
-    while (std::getline(in, line))
-      ++numLines;
-    if (numLines >= fMaxDepth) {
-      // Prune!
-      size_t nPrune = fPruneLength;
-      if (nPrune == (size_t)kPruneLengthDefault) {
-         nPrune = (size_t)(fMaxDepth * 0.8);
-      }
+    // Calculate prune length to use
+    size_t nPrune = fPruneLength;
+    if (nPrune == (size_t)kPruneLengthDefault) {
+      nPrune = (size_t)(fMaxDepth * 0.8);
+    } else if (nPrune > fMaxDepth) {
+      nPrune = fMaxDepth - 1; // fMaxDepth is guaranteed to be > 0.
+    }
+
+    // Don't check for the actual line count of the history file after every
+    // single line. Once every 50% on the way between nPrune and fMaxDepth is
+    // enough.
+    if (fNumHistFileLines < fMaxDepth
+        && (fNumHistFileLines % (fMaxDepth - nPrune)) == 0) {
+      fNumHistFileLines = 0;
+      std::string line;
+      std::ifstream in(fHistFileName.c_str());
+      while (std::getline(in, line))
+        ++fNumHistFileLines;
+    }
 
-      // Don't write our lines - other processes might have
+    size_t numLines = fNumHistFileLines;
+    if (numLines >= fMaxDepth) {
+      // Prune! But don't simply write our lines - other processes might have
       // added their own.
-      in.clear();
-      in.seekg(0);
+      std::string line;
+      std::ifstream in(fHistFileName.c_str());
       std::string pruneFileName = fHistFileName + "_prune";
       std::ofstream out(pruneFileName.c_str());
       if (out) {
@@ -103,10 +116,12 @@ namespace textinput {
         ::unlink(fHistFileName.c_str());
 #endif
         ::rename(pruneFileName.c_str(), fHistFileName.c_str());
+        fNumHistFileLines = nPrune;
       }
     } else {
       std::ofstream out(fHistFileName.c_str(), std::ios_base::app);
       out << fEntries.back() << '\n';
+      ++fNumHistFileLines;
     }
   }
 }

core/textinput/src/textinput/History.h

@@ -58,6 +58,7 @@ namespace textinput {
     std::string fHistFileName; // History file name
     size_t fMaxDepth; // Max number of entries before pruning
     size_t fPruneLength; // Remaining entries after pruning
+    size_t fNumHistFileLines; // Hist file's number of lines at previous access
     std::vector<std::string> fEntries; // Previous input lines
   };
 }