From d83568e568e73694ff15d94b035631d7846d58d2 Mon Sep 17 00:00:00 2001
From: Andrew Nelless <andrew@nelless.net>
Date: Mon, 22 Feb 2016 16:49:24 +0000
Subject: [PATCH] Initial stab at Boost context backend for MTasker

---
 pdns/mtasker_fcontext.cc              | 71 +++++++++++++++++++++++++++
 pdns/recursordist/Makefile.am         |  5 +-
 pdns/recursordist/configure.ac        |  1 +
 pdns/recursordist/mtasker_fcontext.cc |  1 +
 4 files changed, 76 insertions(+), 2 deletions(-)
 create mode 100644 pdns/mtasker_fcontext.cc
 create mode 120000 pdns/recursordist/mtasker_fcontext.cc

diff --git a/pdns/mtasker_fcontext.cc b/pdns/mtasker_fcontext.cc
new file mode 100644
index 000000000..dfe345529
--- /dev/null
+++ b/pdns/mtasker_fcontext.cc
@@ -0,0 +1,71 @@
+#include "mtasker_context.hh"
+#include <exception>
+#include <cassert>
+#include <boost/context/fcontext.hpp>
+
+using boost::context::fcontext_t;
+using boost::context::jump_fcontext;
+using boost::context::make_fcontext;
+
+struct args_t {
+    fcontext_t prev_ctx = nullptr;
+    pdns_ucontext_t* self = nullptr;
+    std::function<void(void)>* work = nullptr;
+};
+
+extern "C" {
+static
+void
+threadWrapper (intptr_t const xargs) {
+    auto args = reinterpret_cast<args_t*>(xargs);
+    auto ctx = args->self;
+    auto work = args->work;
+    jump_fcontext (&ctx->uc_mcontext, args->prev_ctx, 0);
+    args = nullptr;
+
+    try {
+        auto start = std::move (*work);
+        start();
+    } catch (...) {
+        ctx->exception = std::current_exception();
+    }
+
+    auto const next_ctx = ctx->uc_link->uc_mcontext;
+    jump_fcontext (&ctx->uc_mcontext, next_ctx,
+                   static_cast<bool>(ctx->exception));
+#ifdef NDEBUG
+    __builtin_unreachable();
+#endif
+}
+}
+
+pdns_ucontext_t::pdns_ucontext_t
+(): uc_mcontext(nullptr), uc_link(nullptr) {
+}
+
+pdns_ucontext_t::~pdns_ucontext_t
+() {
+}
+
+void
+pdns_swapcontext
+(pdns_ucontext_t& __restrict octx, pdns_ucontext_t const& __restrict ctx) {
+    if (jump_fcontext (&octx.uc_mcontext, ctx.uc_mcontext, 0)) {
+        std::rethrow_exception (ctx.exception);
+    }
+}
+
+void
+pdns_makecontext
+(pdns_ucontext_t& ctx, std::function<void(void)>& start) {
+    assert (ctx.uc_link);
+    assert (ctx.uc_stack.size() >= 8192);
+    assert (!ctx.uc_mcontext);
+    ctx.uc_mcontext = make_fcontext (&ctx.uc_stack[ctx.uc_stack.size()],
+                                     ctx.uc_stack.size(), &threadWrapper);
+    args_t args;
+    args.self = &ctx;
+    args.work = &start;
+    jump_fcontext (&args.prev_ctx, ctx.uc_mcontext,
+                   reinterpret_cast<intptr_t>(&args));
+}
diff --git a/pdns/recursordist/Makefile.am b/pdns/recursordist/Makefile.am
index 48b256030..c73e1d6a6 100644
--- a/pdns/recursordist/Makefile.am
+++ b/pdns/recursordist/Makefile.am
@@ -85,7 +85,7 @@ pdns_recursor_SOURCES = \
 	misc.hh misc.cc \
 	mplexer.hh \
 	mtasker.hh \
-	mtasker_context.hh mtasker_ucontext.cc \
+	mtasker_context.hh mtasker_fcontext.cc \
 	namespaces.hh \
 	nsecrecords.cc \
 	opensslsigners.cc opensslsigners.hh \
@@ -127,7 +127,8 @@ pdns_recursor_SOURCES = \
 pdns_recursor_LDADD = \
 	$(YAHTTP_LIBS) \
 	$(JSON11_LIBS) \
-	$(OPENSSL_LIBS)
+	$(OPENSSL_LIBS) \
+	$(BOOST_CONTEXT_LIBS)
 
 pdns_recursor_LDFLAGS = $(AM_LDFLAGS) \
 	$(OPENSSL_LDFLAGS)
diff --git a/pdns/recursordist/configure.ac b/pdns/recursordist/configure.ac
index 880a99345..72753c92d 100644
--- a/pdns/recursordist/configure.ac
+++ b/pdns/recursordist/configure.ac
@@ -34,6 +34,7 @@ AC_PROG_LIBTOOL
 PDNS_CHECK_OS
 
 BOOST_REQUIRE([1.35])
+BOOST_CONTEXT()
 PDNS_ENABLE_REPRODUCIBLE
 
 PDNS_WITH_LUAJIT
diff --git a/pdns/recursordist/mtasker_fcontext.cc b/pdns/recursordist/mtasker_fcontext.cc
new file mode 120000
index 000000000..cac593d9b
--- /dev/null
+++ b/pdns/recursordist/mtasker_fcontext.cc
@@ -0,0 +1 @@
+../mtasker_fcontext.cc
\ No newline at end of file
-- 
2.40.0