[review] Turn off threaded minsym demangling by default

["Christian Biesinger (Code Review)" <gerrit@gnutoolchain-gerrit.osci.io>]

Change URL: https://gnutoolchain-gerrit.osci.io/r/c/binutils-gdb/+/687
......................................................................

Turn off threaded minsym demangling by default

Per discussion on gdb-patches with Joel, this patch turns off multihreaded
symbol loading by default. It can be turned on using:
  maint set worker-threads unlimited

To keep the behavior as close as possible to the old code, it still
calls symbol_set_names in the old place if n_worker_threads is 0.

gdb/ChangeLog:

2019-11-18  Christian Biesinger  <cbiesinger@google.com>

	* maint.c (n_worker_threads): Default to 0.
	(worker_threads_disabled): New function.
	* maint.h (worker_threads_disabled): New function.
	* minsyms.c (minimal_symbol_reader::record_full): Call symbol_set_names
	here if worker_threads_disabled () is true.
	(minimal_symbol_reader::install): Skip all threading if
	worker_threads_disabled () is true.

Change-Id: I92ba4f6bbf07363189666327cad452d6b9c8e01d
---
M gdb/maint.c
M gdb/maint.h
M gdb/minsyms.c
3 files changed, 47 insertions(+), 30 deletions(-)



diff --git a/gdb/maint.c b/gdb/maint.c
index fce1a1c..3e14c3e 100644
--- a/gdb/maint.c
+++ b/gdb/maint.c
@@ -845,7 +845,12 @@
 }
 #endif
 
-static int n_worker_threads = -1;
+static int n_worker_threads = 0;
+
+bool worker_threads_disabled ()
+{
+  return n_worker_threads == 0;
+}
 
 /* Update the thread pool for the desired number of threads.  */
 static void
diff --git a/gdb/maint.h b/gdb/maint.h
index 827964d..cbaf9de 100644
--- a/gdb/maint.h
+++ b/gdb/maint.h
@@ -26,6 +26,8 @@
 
 extern void set_per_command_space (int);
 
+extern bool worker_threads_disabled ();
+
 /* Records a run time and space usage to be used as a base for
    reporting elapsed time or change in space.  */
 
diff --git a/gdb/minsyms.c b/gdb/minsyms.c
index f9d1172..b59b96d 100644
--- a/gdb/minsyms.c
+++ b/gdb/minsyms.c
@@ -53,6 +53,7 @@
 #include "gdbsupport/symbol.h"
 #include <algorithm>
 #include "safe-ctype.h"
+#include "maint.h"
 #include "gdbsupport/parallel-for.h"
 
 #if CXX_STD_THREAD
@@ -1139,6 +1140,12 @@
   else
     msymbol->name = name.data ();
 
+  if (worker_threads_disabled ())
+    /* To keep our behavior as close as possible to the previous non-threaded
+       behavior for GDB 9.1, we call symbol_set_names here when threads
+       are disabled.  */
+    symbol_set_names (msymbol, msymbol->name, false, m_objfile->per_bfd);
+
   SET_MSYMBOL_VALUE_ADDRESS (msymbol, address);
   MSYMBOL_SECTION (msymbol) = section;
 
@@ -1364,43 +1371,46 @@
       m_objfile->per_bfd->minimal_symbol_count = mcount;
       m_objfile->per_bfd->msymbols = std::move (msym_holder);
 
+      if (!worker_threads_disabled ())
+	{
 #if CXX_STD_THREAD
-      /* Mutex that is used when modifying or accessing the demangled
-	 hash table.  */
-      std::mutex demangled_mutex;
+	  /* Mutex that is used when modifying or accessing the demangled
+	     hash table.  */
+	  std::mutex demangled_mutex;
 #endif
 
-      msymbols = m_objfile->per_bfd->msymbols.get ();
-      gdb::parallel_for_each
-	(&msymbols[0], &msymbols[mcount],
-	 [&] (minimal_symbol *start, minimal_symbol *end)
-	 {
-	   for (minimal_symbol *msym = start; msym < end; ++msym)
+	  msymbols = m_objfile->per_bfd->msymbols.get ();
+	  gdb::parallel_for_each
+	    (&msymbols[0], &msymbols[mcount],
+	     [&] (minimal_symbol *start, minimal_symbol *end)
 	     {
-	       if (!msym->name_set)
+	       for (minimal_symbol *msym = start; msym < end; ++msym)
 		 {
-		   /* This will be freed later, by symbol_set_names.  */
-		   char *demangled_name
-		     = symbol_find_demangled_name (msym, msym->name);
-		   symbol_set_demangled_name
-		     (msym, demangled_name,
-		      &m_objfile->per_bfd->storage_obstack);
-		   msym->name_set = 1;
+		   if (!msym->name_set)
+		     {
+		       /* This will be freed later, by symbol_set_names.  */
+		       char *demangled_name
+			 = symbol_find_demangled_name (msym, msym->name);
+		       symbol_set_demangled_name
+			 (msym, demangled_name,
+			  &m_objfile->per_bfd->storage_obstack);
+		       msym->name_set = 1;
+		     }
 		 }
-	     }
-	   {
-	     /* To limit how long we hold the lock, we only acquire it here
-	        and not while we demangle the names above.  */
-#if CXX_STD_THREAD
-	     std::lock_guard<std::mutex> guard (demangled_mutex);
-#endif
-	     for (minimal_symbol *msym = start; msym < end; ++msym)
 	       {
-		 symbol_set_names (msym, msym->name, false,
-				   m_objfile->per_bfd);
+		 /* To limit how long we hold the lock, we only acquire it here
+		    and not while we demangle the names above.  */
+#if CXX_STD_THREAD
+		 std::lock_guard<std::mutex> guard (demangled_mutex);
+#endif
+		 for (minimal_symbol *msym = start; msym < end; ++msym)
+		   {
+		     symbol_set_names (msym, msym->name, false,
+				       m_objfile->per_bfd);
+		   }
 	       }
-	   }
-	 });
+	     });
+	}
 
       build_minimal_symbol_hash_tables (m_objfile);
     }

-- 
Gerrit-Project: binutils-gdb
Gerrit-Branch: master
Gerrit-Change-Id: I92ba4f6bbf07363189666327cad452d6b9c8e01d
Gerrit-Change-Number: 687
Gerrit-PatchSet: 1
Gerrit-Owner: Christian Biesinger <cbiesinger@google.com>
Gerrit-MessageType: newchange