[lldb] Add new LLDB setting: use-source-cache

Summary:
LLDB memory-maps large source files, and at the same time, caches
all source files in the Source Cache.

On Windows, memory-mapped source files are not writeable, causing
bad user experience in IDEs (such as errors when saving edited files).
IDEs should have the ability to disable the Source Cache at LLDB
startup, so that users can edit source files while debugging.

Bug: llvm.org/PR45310

Reviewers: labath, JDevlieghere, jingham

Reviewed By: labath

Subscribers: lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D76804

lldb/include/lldb/API/SBDebugger.h

@@ -199,6 +199,10 @@ public:
 
   bool GetUseColor() const;
 
+  bool SetUseSourceCache(bool use_source_cache);
+
+  bool GetUseSourceCache() const;
+
   static bool GetDefaultArchitecture(char *arch_name, size_t arch_name_len);
 
   static bool SetDefaultArchitecture(const char *arch_name);

lldb/include/lldb/Core/Debugger.h

@@ -273,6 +273,10 @@ public:
 
   bool SetUseColor(bool use_color);
 
+  bool GetUseSourceCache() const;
+
+  bool SetUseSourceCache(bool use_source_cache);
+
   bool GetHighlightSource() const;
 
   lldb::StopShowColumn GetStopShowColumn() const;

lldb/include/lldb/Core/SourceManager.h

@@ -101,6 +101,9 @@ public:
     void AddSourceFile(const FileSP &file_sp);
     FileSP FindSourceFile(const FileSpec &file_spec) const;
 
+    // Removes all elements from the cache.
+    void Clear() { m_file_cache.clear(); }
+
   protected:
     typedef std::map<FileSpec, FileSP> FileCache;
     FileCache m_file_cache;

lldb/source/API/SBDebugger.cpp

@@ -1374,6 +1374,18 @@ bool SBDebugger::GetUseColor() const {
   return (m_opaque_sp ? m_opaque_sp->GetUseColor() : false);
 }
 
+bool SBDebugger::SetUseSourceCache(bool value) {
+  LLDB_RECORD_METHOD(bool, SBDebugger, SetUseSourceCache, (bool), value);
+
+  return (m_opaque_sp ? m_opaque_sp->SetUseSourceCache(value) : false);
+}
+
+bool SBDebugger::GetUseSourceCache() const {
+  LLDB_RECORD_METHOD_CONST_NO_ARGS(bool, SBDebugger, GetUseSourceCache);
+
+  return (m_opaque_sp ? m_opaque_sp->GetUseSourceCache() : false);
+}
+
 bool SBDebugger::GetDescription(SBStream &description) {
   LLDB_RECORD_METHOD(bool, SBDebugger, GetDescription, (lldb::SBStream &),
                      description);

lldb/source/Core/CoreProperties.td

@@ -103,6 +103,10 @@ let Definition = "debugger" in {
     Global,
     DefaultTrue,
     Desc<"Whether to use Ansi color codes or not.">;
+  def UseSourceCache: Property<"use-source-cache", "Boolean">,
+    Global,
+    DefaultTrue,
+    Desc<"Whether to cache source files in memory or not.">;
   def AutoOneLineSummaries: Property<"auto-one-line-summaries", "Boolean">,
     Global,
     DefaultTrue,

lldb/source/Core/Debugger.cpp

@@ -212,6 +212,11 @@ Status Debugger::SetPropertyValue(const ExecutionContext *exe_ctx,
       // use-color changed. Ping the prompt so it can reset the ansi terminal
       // codes.
       SetPrompt(GetPrompt());
+    } else if (property_path == g_debugger_properties[ePropertyUseSourceCache].name) {
+      // use-source-cache changed. Wipe out the cache contents if it was disabled.
+      if (!GetUseSourceCache()) {
+        m_source_file_cache.Clear();
+      }
     } else if (is_load_script && target_sp &&
                load_script_old_value == eLoadScriptFromSymFileWarn) {
       if (target_sp->TargetProperties::GetLoadScriptFromSymbolFile() ==
@@ -338,6 +343,20 @@ bool Debugger::SetUseColor(bool b) {
   return ret;
 }
 
+bool Debugger::GetUseSourceCache() const {
+  const uint32_t idx = ePropertyUseSourceCache;
+  return m_collection_sp->GetPropertyAtIndexAsBoolean(
+      nullptr, idx, g_debugger_properties[idx].default_uint_value != 0);
+}
+
+bool Debugger::SetUseSourceCache(bool b) {
+  const uint32_t idx = ePropertyUseSourceCache;
+  bool ret = m_collection_sp->SetPropertyAtIndexAsBoolean(nullptr, idx, b);
+  if (!ret) {
+    m_source_file_cache.Clear();
+  }
+  return ret;
+}
 bool Debugger::GetHighlightSource() const {
   const uint32_t idx = ePropertyHighlightSource;
   return m_collection_sp->GetPropertyAtIndexAsBoolean(

lldb/source/Core/SourceManager.cpp

@@ -72,7 +72,7 @@ SourceManager::FileSP SourceManager::GetFile(const FileSpec &file_spec) {
   FileSP file_sp;
   if (same_as_previous)
     file_sp = m_last_file_sp;
-  else if (debugger_sp)
+  else if (debugger_sp && debugger_sp->GetUseSourceCache())
     file_sp = debugger_sp->GetSourceFileCache().FindSourceFile(file_spec);
 
   TargetSP target_sp(m_target_wp.lock());
@@ -95,7 +95,7 @@ SourceManager::FileSP SourceManager::GetFile(const FileSpec &file_spec) {
     else
       file_sp = std::make_shared<File>(file_spec, debugger_sp);
 
-    if (debugger_sp)
+    if (debugger_sp && debugger_sp->GetUseSourceCache())
       debugger_sp->GetSourceFileCache().AddSourceFile(file_sp);
   }
   return file_sp;