base: Add a class which encapsulates Fibers.

This class encapsulates the idea of a Fiber in such a way that other
implementations can be substituted in in the future. This
implementation uses the ucontext family of functions.

This change also adds a new unit test which exercises the new class. It
creates three new fibers which accept a sequence of other fibers to
switch to, one after the other. The main test function switches to
the these fibers which switch with each other and occasionally back to
the main fiber. Each time a test fiber is activated, it checks against
a list which shows the correct order for the fibers to run in. When the
main fiber gets control, it makes sure that list has been progressed
through by the correct amount.

Change-Id: I1fc2afa414b51baaa91e350a4ebc791d989f0b8a
Reviewed-on: https://gem5-review.googlesource.com/10935
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Maintainer: Gabe Black <gabeblack@google.com>

1 files changed, 140 insertions, 0 deletions

diff --git a/src/base/fibertest.cc b/src/base/fibertest.cc
new file mode 100644
index 000000000..5ed13d425
--- /dev/null
+++ b/src/base/fibertest.cc
@@ -0,0 +1,140 @@
+/*
+ * Copyright 2018 Google, Inc.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met: redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer;
+ * redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution;
+ * neither the name of the copyright holders nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Authors: Gabe Black
+ */
+
+#include <gtest/gtest.h>
+
+#include <initializer_list>
+#include <iostream>
+#include <vector>
+
+#include "base/fiber.hh"
+
+class TestFiber : public Fiber
+{
+  public:
+    const char *name;
+    std::vector<Fiber *> next;
+
+    TestFiber(const char *name, std::initializer_list<Fiber *> l);
+
+    void checkExpected();
+    void main();
+};
+
+extern TestFiber a;
+extern TestFiber b;
+extern TestFiber c;
+
+TestFiber a("A", { &b, &a, Fiber::primaryFiber(), &b, &c });
+TestFiber b("B", { &a, &c });
+TestFiber c("C", { &a, Fiber::primaryFiber(), Fiber::primaryFiber() });
+
+std::vector<TestFiber *>::iterator expectedIt;
+std::vector<TestFiber *> expected({
+    &a, &b, &a, &a, /* main Fiber, */
+    &a, &b, &c, &a, &c,
+    /* main Fiber, */ &c, &c
+});
+
+TestFiber::TestFiber(
+        const char *name, std::initializer_list<Fiber *> l) :
+    name(name), next(l)
+{}
+
+void
+TestFiber::checkExpected()
+{
+    ASSERT_NE(expectedIt, expected.end());
+    TestFiber *e = *expectedIt++;
+    EXPECT_EQ(e, this) << "Expected " << e->name << ", got " << name;
+}
+
+void
+TestFiber::main()
+{
+    checkExpected();
+    for (auto &n : next) {
+        n->run();
+        checkExpected();
+    }
+}
+
+TEST(Fiber, Switching)
+{
+    expectedIt = expected.begin();
+
+    a.run();
+    EXPECT_EQ(expectedIt - expected.begin(), 4);
+
+    a.run();
+    EXPECT_EQ(expectedIt - expected.begin(), 9);
+
+    c.run();
+    EXPECT_EQ(expectedIt - expected.begin(), 10);
+
+    EXPECT_FALSE(a.finished());
+    EXPECT_FALSE(b.finished());
+    EXPECT_FALSE(c.finished());
+
+    c.run();
+    EXPECT_EQ(expected.end(), expectedIt) <<
+        "Didn't exactly use up the expected Fiber sequence";
+
+    EXPECT_TRUE(c.finished());
+}
+
+int currentIndex = 0;
+
+class LinkedFiber : public Fiber
+{
+  public:
+    const int index;
+    LinkedFiber(Fiber *link, int index) : Fiber(link), index(index) {}
+
+    void
+    main()
+    {
+        EXPECT_EQ(currentIndex, index);
+        currentIndex++;
+    }
+};
+
+TEST(Fiber, Linked)
+{
+    currentIndex = 0;
+
+    LinkedFiber lf3(Fiber::primaryFiber(), 3);
+    LinkedFiber lf2(&lf3, 2);
+    LinkedFiber lf1(&lf2, 1);
+    LinkedFiber lf0(&lf1, 0);
+
+    lf0.run();
+
+    EXPECT_EQ(currentIndex, 4);
+}