Adds static tape functions to control tape activation

docs/ref/tape.md

@@ -116,6 +116,19 @@ or `!c++ nullptr` if no active tape has been set.
 Note that this is a thread-local pointer - calling this function in different
 threads gives different results.
 
+#### `setActive`
+
+`#!c++ static void setActive(Tape* t)` static function that sets the given tape as the
+globally active one. This is equivalent to `t.activate()`. 
+
+It may throw [`TapeAlreadyActive`](exceptions.md) if another tape is
+already active for the current thread.
+
+#### `deactivateAll`
+
+`#!c++ static void deactivateAll()` deactivates any currently active tapes. 
+Equivalent to `auto t = Tape::getActive(); if (t) t->deactivate();`.
+
 #### `registerInput`
 
 `#!c++ void registerInput(active_type& inp)` registers the given variable with the tape and start recording dependents of it. A call to this function or its overloads is required in order to calculate adjoints.

src/XAD/Tape.hpp

@@ -91,13 +91,8 @@ class Tape
     Tape& operator=(const Tape&) = delete;
 
     // recording control
-    XAD_INLINE void activate()
-    {
-        if (active_tape_ != nullptr)
-            throw TapeAlreadyActive();
-        else
-            active_tape_ = this;
-    }
+    XAD_INLINE void activate() { setActive(this); }
+
     XAD_INLINE void deactivate()
     {
         if (active_tape_ == this)
@@ -106,6 +101,16 @@ class Tape
     XAD_INLINE bool isActive() const { return active_tape_ == this; }
     XAD_INLINE static Tape* getActive() { return active_tape_; }
 
+    XAD_INLINE static void setActive(Tape* t)
+    {
+        if (active_tape_ != nullptr)
+            throw TapeAlreadyActive();
+        else
+            active_tape_ = t;
+    }
+
+    XAD_INLINE static void deactivateAll() { active_tape_ = nullptr; }
+
     XAD_INLINE void registerInput(active_type& inp)
     {
         if (!inp.shouldRecord())  // already registered

test/Tape_test.cpp

@@ -62,6 +62,33 @@ TEST(Tape, canInitializeDeactivated)
     EXPECT_NE(nullptr, Tape<float>::getActive());
 }
 
+TEST(Tape, canActivateStatically)
+{
+    using xad::Tape;
+    Tape<float> s(false);
+
+    EXPECT_FALSE(s.isActive());
+    EXPECT_EQ(nullptr, Tape<float>::getActive());
+
+    xad::Tape<float>::setActive(&s);
+
+    EXPECT_TRUE(s.isActive());
+    EXPECT_NE(nullptr, Tape<float>::getActive());
+}
+
+TEST(Tape, canDeactivateGlobally)
+{
+    using xad::Tape;
+
+    EXPECT_EQ(nullptr, Tape<double>::getActive());
+
+    Tape<double> s;
+
+    EXPECT_TRUE(s.isActive());
+    Tape<double>::deactivateAll();
+    EXPECT_FALSE(s.isActive());
+}
+
 TEST(Tape, isMovable)
 {
     xad::Tape<double> s(false);