Cache loaded source signatures safely

src/lib/compiler.cpp

@@ -6,7 +6,9 @@
 #include <cctype>
 #include <filesystem>
 #include <fcntl.h>
+#include <mutex>
 #include <sys/file.h>
+#include <sys/stat.h>
 #include <unistd.h>
 
 namespace {
@@ -43,6 +45,19 @@ struct SharedUnitCompileCheck
 	bool needs_compile = false;
 };
 
+struct UnitSourceSignatureEntry
+{
+	u64 modified_ns = 0;
+	u64 changed_ns = 0;
+	u64 size = 0;
+	String content_hash;
+	StringList loaded_paths;
+};
+
+const u64 UCE_UNIT_SOURCE_SIGNATURE_CACHE_MAX = 4096;
+std::mutex unit_source_signature_cache_mutex;
+std::map<String, UnitSourceSignatureEntry> unit_source_signature_cache;
+
 bool compiler_jit_compile_on_request_enabled(Request* context)
 {
 	if(!context || !context->server)
@@ -113,6 +128,33 @@ StringList compiler_unit_load_paths(String file_name, String content)
 	return(paths);
 }
 
+UnitSourceSignatureEntry compiler_unit_source_entry(String file_name)
+{
+	struct stat info;
+	UnitSourceSignatureEntry entry;
+	if(stat(file_name.c_str(), &info) != 0)
+		return(entry);
+	entry.modified_ns = (u64)info.st_mtim.tv_sec * 1000000000ull + (u64)info.st_mtim.tv_nsec;
+	entry.changed_ns = (u64)info.st_ctim.tv_sec * 1000000000ull + (u64)info.st_ctim.tv_nsec;
+	entry.size = (u64)info.st_size;
+	{
+		std::lock_guard<std::mutex> lock(unit_source_signature_cache_mutex);
+		auto cached = unit_source_signature_cache.find(file_name);
+		if(cached != unit_source_signature_cache.end() && cached->second.modified_ns == entry.modified_ns && cached->second.changed_ns == entry.changed_ns && cached->second.size == entry.size)
+			return(cached->second);
+	}
+	String content = file_get_contents(file_name);
+	entry.content_hash = gen_sha1(content);
+	entry.loaded_paths = compiler_unit_load_paths(file_name, content);
+	{
+		std::lock_guard<std::mutex> lock(unit_source_signature_cache_mutex);
+		if(unit_source_signature_cache.size() >= UCE_UNIT_SOURCE_SIGNATURE_CACHE_MAX)
+			unit_source_signature_cache.clear();
+		unit_source_signature_cache[file_name] = entry;
+	}
+	return(entry);
+}
+
 void compiler_append_unit_source_signature(String file_name, std::set<String>& visited, String& signature)
 {
 	String normalized = path_real(file_name);
@@ -122,9 +164,9 @@ void compiler_append_unit_source_signature(String file_name, std::set<String>& v
 		return;
 	visited.insert(normalized);
 
-	String content = file_get_contents(file_name);
-	signature += normalized + ":" + gen_sha1(content) + "\n";
-	for(String loaded : compiler_unit_load_paths(file_name, content))
+	UnitSourceSignatureEntry entry = compiler_unit_source_entry(normalized);
+	signature += normalized + ":" + entry.content_hash + "\n";
+	for(String loaded : entry.loaded_paths)
 		compiler_append_unit_source_signature(loaded, visited, signature);
 }