[review] [RFC] Don't block on finishing demangling msymbols

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

Christian Biesinger has posted comments on this change.

Change URL: https://gnutoolchain-gerrit.osci.io/r/c/binutils-gdb/+/463
......................................................................


Patch Set 1:

(1 comment)

| --- gdb/minsyms.c
| +++ gdb/minsyms.c
| @@ -335,18 +335,19 @@ lookup_minimal_symbol (const char *name, const char *sfile,
|  	{
|  	  if (symbol_lookup_debug)
|  	    {
|  	      fprintf_unfiltered (gdb_stdlog,
|  				  "lookup_minimal_symbol (%s, %s, %s)\n",
|  				  name, sfile != NULL ? sfile : "NULL",
|  				  objfile_debug_name (objfile));
|  	    }
|  
| +	  objfile->per_bfd->wait_for_msymbols ();

PS1, Line 344:

So the problem here is that the hash tables, at least
demangled_names_hash, isn't just an output, it's really an inout
parameter when you have multiple minsym readers installed for the same
bfd. There's also the issue that with the future you have to be
careful to std::move everywhere so as not to introduce extra copies.

I was thinking something like this:

 class BlockedOnFuture<T> {
   T contents;
   std::future<void> future;

   T& get() { if (future.valid()) future.wait(); return contents; }
   T& operator->() { return get(); }

   void set_future(std::future<void>& f) { future = f; }
 };

And T here would be a struct with the hashtables.

That way we'll set the future when we start the symbol reading and
everything will work in a straightforward way.

WDYT?

|  	  /* Do two passes: the first over the ordinary hash table,
|  	     and the second over the demangled hash table.  */
|  	  lookup_minimal_symbol_mangled (name, sfile, objfile,
|  					 objfile->per_bfd->msymbol_hash,
|  					 mangled_hash, mangled_cmp, found);
|  
|  	  /* If not found, try the demangled hash table.  */
|  	  if (found.external_symbol.minsym == NULL)
|  	    {

-- 
Gerrit-Project: binutils-gdb
Gerrit-Branch: master
Gerrit-Change-Id: I9d871917459ece0b41d31670b3c56600757aea66
Gerrit-Change-Number: 463
Gerrit-PatchSet: 1
Gerrit-Owner: Christian Biesinger <cbiesinger@google.com>
Gerrit-Reviewer: Christian Biesinger <cbiesinger@google.com>
Gerrit-CC: Tom Tromey <tromey@sourceware.org>
Gerrit-Comment-Date: Wed, 27 Nov 2019 23:07:13 +0000
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Comment-In-Reply-To: Christian Biesinger <cbiesinger@google.com>
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