Improve string cache footprint

Use "insert" to find or insert an entry, and tell us which happened, rather than a magic flag in the cache entry to say its new or not.
peadar · Jun 11, 2024 · a76b7ca · a76b7ca
1 parent e3144a2
commit a76b7ca
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Showing 2 changed files with 5 additions and 11 deletions.
diff --git a/libpstack/reader.h b/libpstack/reader.h
@@ -113,12 +113,8 @@ class FileReader : public Reader {
 // Reader implementations
 
 class CacheReader final : public Reader {
-    struct CacheEnt {
-        std::string value;
-        bool isNew = true;
-    };
     Reader::csptr upstream;
-    mutable std::unordered_map<Off, CacheEnt> stringCache;
+    mutable std::unordered_map<Off, std::string> stringCache;
     static const size_t PAGESIZE = 256;
     static const size_t MAXPAGES = 16;
     class Page {

diff --git a/reader.cc b/reader.cc
@@ -186,12 +186,10 @@ CacheReader::read(Off off, size_t count, char *ptr) const
 string
 CacheReader::readString(Off off) const
 {
-    auto &entry = stringCache[off];
-    if (entry.isNew) {
-        entry.value = Reader::readString(off);
-        entry.isNew = false;
-    }
-    return entry.value;
+    auto [it, neu] = stringCache.insert(std::make_pair(off, std::string{}));
+    if (neu)
+        it->second = Reader::readString(off);
+    return it->second;
 }
 
 Reader::csptr