Fix latent bug with context locking in placer HeAP.

Signed-off-by: Keith Rothman <537074+litghost@users.noreply.github.com>

common/placer_heap.cc

@@ -49,6 +49,7 @@
 #include "nextpnr.h"
 #include "place_common.h"
 #include "placer1.h"
+#include "scope_lock.h"
 #include "timing.h"
 #include "util.h"
 
@@ -147,7 +148,7 @@ class HeAPPlacer
     {
         auto startt = std::chrono::high_resolution_clock::now();
 
-        ctx->lock();
+        nextpnr::ScopeLock<Context> lock(ctx);
         place_constraints();
         build_fast_bels();
         seed_placement();
@@ -312,15 +313,6 @@ class HeAPPlacer
                 log_info("AP soln: %s -> %s\n", cell.first.c_str(ctx), ctx->nameOfBel(cell.second->bel));
         }
 
-        ctx->unlock();
-        auto endtt = std::chrono::high_resolution_clock::now();
-        log_info("HeAP Placer Time: %.02fs\n", std::chrono::duration<double>(endtt - startt).count());
-        log_info("  of which solving equations: %.02fs\n", solve_time);
-        log_info("  of which spreading cells: %.02fs\n", cl_time);
-        log_info("  of which strict legalisation: %.02fs\n", sl_time);
-
-        ctx->check();
-
         bool any_bad_placements = false;
         for (auto bel : ctx->getBels()) {
             CellInfo *cell = ctx->getBoundBelCell(bel);
@@ -339,6 +331,16 @@ class HeAPPlacer
             return false;
         }
 
+        lock.unlock_early();
+
+        auto endtt = std::chrono::high_resolution_clock::now();
+        log_info("HeAP Placer Time: %.02fs\n", std::chrono::duration<double>(endtt - startt).count());
+        log_info("  of which solving equations: %.02fs\n", solve_time);
+        log_info("  of which spreading cells: %.02fs\n", cl_time);
+        log_info("  of which strict legalisation: %.02fs\n", sl_time);
+
+        ctx->check();
+
         if (!placer1_refine(ctx, Placer1Cfg(ctx))) {
             return false;
         }

common/scope_lock.h

@@ -0,0 +1,56 @@
+/*
+ *  nextpnr -- Next Generation Place and Route
+ *
+ *  Copyright (C) 2021 Symbiflow Authors.
+ *
+ *  Permission to use, copy, modify, and/or distribute this software for any
+ *  purpose with or without fee is hereby granted, provided that the above
+ *  copyright notice and this permission notice appear in all copies.
+ *
+ *  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ *  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ *  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ *  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ *  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ *  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ *  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ */
+
+#ifndef SCOPE_LOCK_H
+#define SCOPE_LOCK_H
+
+namespace nextpnr {
+
+// Provides a simple RIAA locking object.  ScopeLock takes a lock when
+// constructed, and releases the lock on destruction or if "unlock_early" is
+// called.
+//
+// LockingObject must have a method "void lock(void)" and "void unlock(void)".
+template<typename LockingObject>
+class ScopeLock {
+public:
+    ScopeLock(LockingObject * obj) : obj_(obj), locked_(false) {
+        obj_->lock();
+        locked_ = true;
+    }
+    ScopeLock(const ScopeLock &other) = delete;
+    ScopeLock(const ScopeLock &&other) = delete;
+
+    ~ScopeLock() {
+        if(locked_) {
+            obj_->unlock();
+        }
+    }
+    void unlock_early() {
+        locked_ = false;
+        obj_->unlock();
+    }
+private:
+    LockingObject *obj_;
+    bool locked_;
+};
+
+};
+
+#endif /* SCOPE_LOCK_H */