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/*
* This file is part of PowerDNS or dnsdist.
* Copyright -- PowerDNS.COM B.V. and its contributors
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of version 2 of the GNU General Public License as
* published by the Free Software Foundation.
*
* In addition, for the avoidance of any doubt, permission is granted to
* link this program with OpenSSL and to (re)distribute the binaries
* produced as the result of such linking.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#include "mtasker_context.hh"
#include <exception>
#include <cassert>
#include <type_traits>
#include <boost/version.hpp>
#if BOOST_VERSION < 106100
#include <boost/context/fcontext.hpp>
using boost::context::make_fcontext;
#else
#include <boost/context/detail/fcontext.hpp>
using boost::context::detail::make_fcontext;
#endif /* BOOST_VERSION < 106100 */
#if BOOST_VERSION < 105600
/* Note: This typedef means functions taking fcontext_t*, like jump_fcontext(),
* now require a reinterpret_cast rather than a static_cast, since we're
* casting from pdns_context_t->uc_mcontext, which is void**, to
* some_opaque_struct**. In later versions fcontext_t is already void*. So if
* you remove this, then fix the ugly.
*/
using fcontext_t = boost::context::fcontext_t*;
/* Emulate the >= 1.56 API for Boost 1.52 through 1.55 */
static inline intptr_t
jump_fcontext (fcontext_t* const ofc, fcontext_t const nfc,
intptr_t const arg) {
/* If the fcontext_t is preallocated then use it, otherwise allocate one
* on the stack ('self') and stash a pointer away in *ofc so the returning
* MThread can access it. This is safe because we're suspended, so the
* context object always outlives the jump.
*/
if (*ofc) {
return boost::context::jump_fcontext (*ofc, nfc, arg);
} else {
boost::context::fcontext_t self;
*ofc = &self;
auto ret = boost::context::jump_fcontext (*ofc, nfc, arg);
*ofc = nullptr;
return ret;
}
}
#else
#if BOOST_VERSION < 106100
using boost::context::fcontext_t;
using boost::context::jump_fcontext;
#else
using boost::context::detail::fcontext_t;
using boost::context::detail::jump_fcontext;
using boost::context::detail::transfer_t;
#endif /* BOOST_VERSION < 106100 */
static_assert (std::is_pointer<fcontext_t>::value,
"Boost Context has changed the fcontext_t type again :-(");
#endif
/* Boost context only provides a means of passing a single argument across a
* jump. args_t simply provides a way to pass more by reference.
*/
struct args_t {
#if BOOST_VERSION < 106100
fcontext_t prev_ctx = nullptr;
#endif
pdns_ucontext_t* self = nullptr;
boost::function<void(void)>* work = nullptr;
};
extern "C" {
static
void
#if BOOST_VERSION < 106100
threadWrapper (intptr_t const xargs) {
#else
threadWrapper (transfer_t const t) {
#endif
/* Access the args passed from pdns_makecontext, and copy them directly from
* the calling stack on to ours (we're now using the MThreads stack).
* This saves heap allocating an args object, at the cost of an extra
* context switch to fashion this constructor-like init phase. The work
* function object is still only moved after we're (re)started, so may
* still be set or changed after a call to pdns_makecontext. This matches
* the behaviour of the System V implementation, which can inherently only
* be passed ints and pointers.
*/
#if BOOST_VERSION < 106100
auto args = reinterpret_cast<args_t*>(xargs);
#else
auto args = reinterpret_cast<args_t*>(t.data);
#endif
auto ctx = args->self;
auto work = args->work;
/* we switch back to pdns_makecontext() */
#if BOOST_VERSION < 106100
jump_fcontext (reinterpret_cast<fcontext_t*>(&ctx->uc_mcontext),
static_cast<fcontext_t>(args->prev_ctx), 0);
#else
transfer_t res = jump_fcontext (t.fctx, 0);
/* we got switched back from pdns_swapcontext() */
if (res.data) {
/* if res.data is not a nullptr, it holds a pointer to the context
we just switched from, and we need to fill it to be able to
switch back to it later. */
fcontext_t* ptr = static_cast<fcontext_t*>(res.data);
*ptr = res.fctx;
}
#endif
args = nullptr;
try {
auto start = std::move (*work);
start();
} catch (...) {
ctx->exception = std::current_exception();
}
/* Emulate the System V uc_link feature. */
auto const next_ctx = ctx->uc_link->uc_mcontext;
#if BOOST_VERSION < 106100
jump_fcontext (reinterpret_cast<fcontext_t*>(&ctx->uc_mcontext),
static_cast<fcontext_t>(next_ctx),
static_cast<bool>(ctx->exception));
#else
jump_fcontext (static_cast<fcontext_t>(next_ctx), 0);
#endif
#ifdef NDEBUG
__builtin_unreachable();
#endif
}
}
pdns_ucontext_t::pdns_ucontext_t
(): uc_mcontext(nullptr), uc_link(nullptr) {
}
pdns_ucontext_t::~pdns_ucontext_t
() {
/* There's nothing to delete here since fcontext doesn't require anything
* to be heap allocated.
*/
}
void
pdns_swapcontext
(pdns_ucontext_t& __restrict octx, pdns_ucontext_t const& __restrict ctx) {
/* we either switch back to threadwrapper() if it's the first time,
or we switch back to pdns_swapcontext(),
in both case we will be returning from a call to jump_fcontext(). */
#if BOOST_VERSION < 106100
if (jump_fcontext (reinterpret_cast<fcontext_t*>(&octx.uc_mcontext),
static_cast<fcontext_t>(ctx.uc_mcontext), 0)) {
std::rethrow_exception (ctx.exception);
}
#else
transfer_t res = jump_fcontext (static_cast<fcontext_t>(ctx.uc_mcontext), &octx.uc_mcontext);
if (res.data) {
/* if res.data is not a nullptr, it holds a pointer to the context
we just switched from, and we need to fill it to be able to
switch back to it later. */
fcontext_t* ptr = static_cast<fcontext_t*>(res.data);
*ptr = res.fctx;
}
if (ctx.exception) {
std::rethrow_exception (ctx.exception);
}
#endif
}
void
pdns_makecontext
(pdns_ucontext_t& ctx, boost::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;
/* jumping to threadwrapper */
#if BOOST_VERSION < 106100
jump_fcontext (reinterpret_cast<fcontext_t*>(&args.prev_ctx),
static_cast<fcontext_t>(ctx.uc_mcontext),
reinterpret_cast<intptr_t>(&args));
#else
transfer_t res = jump_fcontext (static_cast<fcontext_t>(ctx.uc_mcontext),
&args);
/* back from threadwrapper, updating the context */
ctx.uc_mcontext = res.fctx;
#endif
}
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