Re: why does gccgit require pthread?

[Jonathan Wakely <jwakely.gcc@gmail.com>]

On Mon, 7 Nov 2022 at 06:51, LIU Hao via Gcc <gcc@gcc.gnu.org> wrote:
>
> 在 2022-11-07 12:37, Andrew Pinski 写道:
> >
> > The original code which used pthread was added in GCC 5 way before GCC
> > moved to being written in C++11 which was only in the last 3 years.
> > pthread_* functions were the best choice at the time (2014) but now
> > GCC is written in C++11, I don't see any reason not to move them over
> > to using C++11 threading code.
> >
> >
>
> Attached is the proposed patch.

It would be a lot nicer if playback::context met the C++ Lockable
requirements, and playback::context::compile () could just take a
scoped lock on *this:


--- a/gcc/jit/jit-playback.cc
+++ b/gcc/jit/jit-playback.cc
@@ -2353,15 +2353,12 @@ compile ()
  m_recording_ctxt->get_all_requested_dumps (&requested_dumps);

  /* Acquire the JIT mutex and set "this" as the active playback ctxt.  */
-  acquire_mutex ();
+  std::lock_guard<context> lock(*this);

  auto_string_vec fake_args;
  make_fake_args (&fake_args, ctxt_progname, &requested_dumps);
  if (errors_occurred ())
-    {
-      release_mutex ();
-      return;
-    }
+    return;

  /* This runs the compiler.  */
  toplev toplev (get_timer (), /* external_timer */
@@ -2388,10 +2385,7 @@ compile ()
     followup activities use timevars, which are global state.  */

  if (errors_occurred ())
-    {
-      release_mutex ();
-      return;
-    }
+    return;

  if (get_bool_option (GCC_JIT_BOOL_OPTION_DUMP_GENERATED_CODE))
    dump_generated_code ();
@@ -2403,8 +2397,6 @@ compile ()
     convert the .s file to the requested output format, and copy it to a
     given file (playback::compile_to_file).  */
  postprocess (ctxt_progname);
-
-  release_mutex ();
}

/* Implementation of class gcc::jit::playback::compile_to_memory,
@@ -2662,18 +2654,18 @@ playback::compile_to_file::copy_file (const
char *src_path,
/* This mutex guards gcc::jit::recording::context::compile, so that only
   one thread can be accessing the bulk of GCC's state at once.  */

-static pthread_mutex_t jit_mutex = PTHREAD_MUTEX_INITIALIZER;
+static std::mutex jit_mutex;

/* Acquire jit_mutex and set "this" as the active playback ctxt.  */

void
-playback::context::acquire_mutex ()
+playback::context::lock ()
{
  auto_timevar tv (get_timer (), TV_JIT_ACQUIRING_MUTEX);

  /* Acquire the big GCC mutex. */
  JIT_LOG_SCOPE (get_logger ());
-  pthread_mutex_lock (&jit_mutex);
+  jit_mutex.lock();
  gcc_assert (active_playback_ctxt == NULL);
  active_playback_ctxt = this;
}
@@ -2681,13 +2673,13 @@ playback::context::acquire_mutex ()
/* Release jit_mutex and clear the active playback ctxt.  */

void
-playback::context::release_mutex ()
+playback::context::unlock ()
{
  /* Release the big GCC mutex. */
  JIT_LOG_SCOPE (get_logger ());
  gcc_assert (active_playback_ctxt == this);
  active_playback_ctxt = NULL;
-  pthread_mutex_unlock (&jit_mutex);
+  jit_mutex.unlock();
}

/* Callback used by gcc::jit::playback::context::make_fake_args when
diff --git a/gcc/jit/jit-playback.h b/gcc/jit/jit-playback.h
index 3ba02a0451a..bd2bc389f53 100644
--- a/gcc/jit/jit-playback.h
+++ b/gcc/jit/jit-playback.h
@@ -314,8 +314,8 @@ private:

  /* Functions for implementing "compile".  */

-  void acquire_mutex ();
-  void release_mutex ();
+  void lock ();
+  void unlock ();

  void
  make_fake_args (vec <char *> *argvec,