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Remove hacks to support evaluation from coroutines

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Since we're not doing this anymore.
This commit is contained in:
Eelco Dolstra 2024-07-22 15:28:21 +02:00
parent 609df83c01
commit ca0f7db843
4 changed files with 2 additions and 213 deletions
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132
src/libexpr/eval-gc.cc
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@ -30,120 +30,6 @@ static void * oomHandler(size_t requested)
throw std::bad_alloc();
}
class BoehmGCStackAllocator : public StackAllocator
{
boost::coroutines2::protected_fixedsize_stack stack{
// We allocate 8 MB, the default max stack size on NixOS.
// A smaller stack might be quicker to allocate but reduces the stack
// depth available for source filter expressions etc.
std::max(boost::context::stack_traits::default_size(), static_cast<std::size_t>(8 * 1024 * 1024))};
// This is specific to boost::coroutines2::protected_fixedsize_stack.
// The stack protection page is included in sctx.size, so we have to
// subtract one page size from the stack size.
std::size_t pfss_usable_stack_size(boost::context::stack_context & sctx)
{
return sctx.size - boost::context::stack_traits::page_size();
}
public:
boost::context::stack_context allocate() override
{
auto sctx = stack.allocate();
// Stacks generally start at a high address and grow to lower addresses.
// Architectures that do the opposite are rare; in fact so rare that
// boost_routine does not implement it.
// So we subtract the stack size.
GC_add_roots(static_cast<char *>(sctx.sp) - pfss_usable_stack_size(sctx), sctx.sp);
return sctx;
}
void deallocate(boost::context::stack_context sctx) override
{
GC_remove_roots(static_cast<char *>(sctx.sp) - pfss_usable_stack_size(sctx), sctx.sp);
stack.deallocate(sctx);
}
};
static BoehmGCStackAllocator boehmGCStackAllocator;
/**
* When a thread goes into a coroutine, we lose its original sp until
* control flow returns to the thread.
* While in the coroutine, the sp points outside the thread stack,
* so we can detect this and push the entire thread stack instead,
* as an approximation.
* The coroutine's stack is covered by `BoehmGCStackAllocator`.
* This is not an optimal solution, because the garbage is scanned when a
* coroutine is active, for both the coroutine and the original thread stack.
* However, the implementation is quite lean, and usually we don't have active
* coroutines during evaluation, so this is acceptable.
*/
void fixupBoehmStackPointer(void ** sp_ptr, void * _pthread_id)
{
void *& sp = *sp_ptr;
auto pthread_id = reinterpret_cast<pthread_t>(_pthread_id);
pthread_attr_t pattr;
size_t osStackSize;
// The low address of the stack, which grows down.
void * osStackLimit;
void * osStackBase;
# ifdef __APPLE__
osStackSize = pthread_get_stacksize_np(pthread_id);
osStackLimit = pthread_get_stackaddr_np(pthread_id);
# else
if (pthread_attr_init(&pattr)) {
throw Error("fixupBoehmStackPointer: pthread_attr_init failed");
}
# ifdef HAVE_PTHREAD_GETATTR_NP
if (pthread_getattr_np(pthread_id, &pattr)) {
throw Error("fixupBoehmStackPointer: pthread_getattr_np failed");
}
# elif HAVE_PTHREAD_ATTR_GET_NP
if (!pthread_attr_init(&pattr)) {
throw Error("fixupBoehmStackPointer: pthread_attr_init failed");
}
if (!pthread_attr_get_np(pthread_id, &pattr)) {
throw Error("fixupBoehmStackPointer: pthread_attr_get_np failed");
}
# else
# error "Need one of `pthread_attr_get_np` or `pthread_getattr_np`"
# endif
if (pthread_attr_getstack(&pattr, &osStackLimit, &osStackSize)) {
throw Error("fixupBoehmStackPointer: pthread_attr_getstack failed");
}
if (pthread_attr_destroy(&pattr)) {
throw Error("fixupBoehmStackPointer: pthread_attr_destroy failed");
}
# endif
osStackBase = (char *) osStackLimit + osStackSize;
// NOTE: We assume the stack grows down, as it does on all architectures we support.
// Architectures that grow the stack up are rare.
if (sp >= osStackBase || sp < osStackLimit) { // sp is outside the os stack
sp = osStackLimit;
}
}
/* Disable GC while this object lives. Used by CoroutineContext.
*
* Boehm keeps a count of GC_disable() and GC_enable() calls,
* and only enables GC when the count matches.
*/
class BoehmDisableGC
{
public:
BoehmDisableGC()
{
GC_disable();
};
~BoehmDisableGC()
{
GC_enable();
};
};
static inline void initGCReal()
{
/* Initialise the Boehm garbage collector. */
@ -164,24 +50,6 @@ static inline void initGCReal()
GC_set_oom_fn(oomHandler);
StackAllocator::defaultAllocator = &boehmGCStackAllocator;
// TODO: Remove __APPLE__ condition.
// Comment suggests an implementation that works on darwin and windows
// https://github.com/ivmai/bdwgc/issues/362#issuecomment-1936672196
# if GC_VERSION_MAJOR >= 8 && GC_VERSION_MINOR >= 2 && GC_VERSION_MICRO >= 4 && !defined(__APPLE__)
GC_set_sp_corrector(&fixupBoehmStackPointer);
if (!GC_get_sp_corrector()) {
printTalkative("BoehmGC on this platform does not support sp_corrector; will disable GC inside coroutines");
/* Used to disable GC when entering coroutines on macOS */
create_coro_gc_hook = []() -> std::shared_ptr<void> { return std::make_shared<BoehmDisableGC>(); };
}
# else
# warning \
"BoehmGC version does not support GC while coroutine exists. GC will be disabled inside coroutines. Consider updating bdw-gc to 8.2.4 or later."
# endif
/* Set the initial heap size to something fairly big (25% of
physical RAM, up to a maximum of 384 MiB) so that in most cases
we don't need to garbage collect at all. (Collection has a