Reduce memory use for simulations that run in zero time.

The fix for pr1830834 causes vvp to only delete a completed thread
when the simulation time next advances. If a procedural model is
being simulated which makes many task or function calls within a
single time step, this can lead to excessive memory use. This patch
modifies the behaviour so that thread deletion is only delayed if
that thread has caused a sync event to be placed in the event queue.
This should catch all cases where the thread private data can be
accessed after a thread has terminated.
(cherry picked from commit c7b0aef414)

vvp/schedule.cc

@@ -669,6 +669,9 @@ void schedule_generic(vvp_gen_event_t obj, vvp_time64_t delay,
       cur->delete_obj_when_done = delete_when_done;
       schedule_event_(cur, delay,
 		      sync_flag? (ro_flag?SEQ_ROSYNC:SEQ_RWSYNC) : SEQ_ACTIVE);
+
+      if (sync_flag)
+	    vthread_delay_delete();
 }
 
 void schedule_at_start_of_simtime(vvp_gen_event_t obj, vvp_time64_t delay)

vvp/vthread.cc

@@ -111,6 +111,7 @@ struct vthread_s {
       unsigned i_have_ended      :1;
       unsigned waiting_for_event :1;
       unsigned is_scheduled      :1;
+      unsigned delay_delete      :1;
       unsigned fork_count        :8;
 	/* This points to the sole child of the thread. */
       struct vthread_s*child;
@@ -411,6 +412,7 @@ vthread_t vthread_new(vvp_code_t pc, struct __vpiScope*scope)
       thr->schedule_parent_on_end = 0;
       thr->is_scheduled = 0;
       thr->i_have_ended = 0;
+      thr->delay_delete = 0;
       thr->waiting_for_event = 0;
       thr->fork_count   = 0;
       thr->event  = 0;
@@ -498,7 +500,10 @@ static void vthread_reap(vthread_t thr)
       if ((thr->is_scheduled == 0) && (thr->waiting_for_event == 0)) {
 	    assert(thr->fork_count == 0);
 	    assert(thr->wait_next == 0);
-	    schedule_del_thr(thr);
+	    if (thr->delay_delete)
+		  schedule_del_thr(thr);
+	    else
+		  vthread_delete(thr);
       }
 }
 
@@ -517,6 +522,12 @@ void vthread_mark_scheduled(vthread_t thr)
       }
 }
 
+void vthread_delay_delete()
+{
+      if (running_thread)
+	    running_thread->delay_delete = 1;
+}
+
 /*
  * This function runs each thread by fetching an instruction,
  * incrementing the PC, and executing the instruction. The thread may
@@ -4541,9 +4552,12 @@ bool of_XOR(vthread_t thr, vvp_code_t cp)
 bool of_ZOMBIE(vthread_t thr, vvp_code_t)
 {
       thr->pc = codespace_null();
-      if ((thr->parent == 0) && (thr->child == 0))
+      if ((thr->parent == 0) && (thr->child == 0)) {
-	    schedule_del_thr(thr);
+	    if (thr->delay_delete)
-
+		  schedule_del_thr(thr);
+	    else
+		  vthread_delete(thr);
+      }
       return false;
 }
 

vvp/vthread.h

@@ -1,7 +1,7 @@
 #ifndef __vthread_H
 #define __vthread_H
 /*
- * Copyright (c) 2001-2008 Stephen Williams (steve@icarus.com)
+ * Copyright (c) 2001-2009 Stephen Williams (steve@icarus.com)
  *
  *    This source code is free software; you can redistribute it
  *    and/or modify it in source code form under the terms of the GNU
@@ -48,6 +48,14 @@ extern vthread_t vthread_new(vvp_code_t sa, struct __vpiScope*scope);
  */
 extern void vthread_mark_scheduled(vthread_t thr);
 
+/*
+ * This function causes deletion of the currently running thread to
+ * be delayed until after all sync events have been processed for the
+ * time step in which the thread terminates. It is only used by the
+ * schedule_generic function.
+ */
+extern void vthread_delay_delete();
+
 /*
  * Cause this thread to execute instructions until in is put to sleep
  * by executing some sort of delay or wait instruction.