libstdc++: Make pmr::synchronized_pool_resource work without libpthread (PR 94936)
I implicitly assumed that programs using pmr::synchronized_pool_resource would also be using multiple threads, and so the weak symbols in gthr-posix.h would be resolved by linking to libpthread. If that isn't true then it crashes when trying to use pthread_key_create. This commit makes the pool resource check __gthread_active_p() before using thread-specific data, and just use a single set of memory pools when there's only a single thread. PR libstdc++/94936 * src/c++17/memory_resource.cc (synchronized_pool_resource::_TPools): Add comment about single-threaded behaviour. (synchronized_pool_resource::_TPools::move_nonempty_chunks()): Hoist class member access out of loop. (synchronized_pool_resource::synchronized_pool_resource()) (synchronized_pool_resource::~synchronized_pool_resource()) (synchronized_pool_resource::release()): Check __gthread_active_p before creating and/or deleting the thread-specific data key. (synchronized_pool_resource::_M_thread_specific_pools()): Adjust assertions. (synchronized_pool_resource::do_allocate(size_t, size_t)): Add fast path for single-threaded case. (synchronized_pool_resource::do_deallocate(void*, size_t, size_t)): Likewise. Return if unable to find a pool that owns the allocation. * testsuite/20_util/synchronized_pool_resource/allocate_single.cc: New test. * testsuite/20_util/synchronized_pool_resource/cons_single.cc: New test. * testsuite/20_util/synchronized_pool_resource/release_single.cc: New test.
This commit is contained in:
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@ -1,3 +1,27 @@
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2020-05-04 Jonathan Wakely <jwakely@redhat.com>
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PR libstdc++/94936
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* src/c++17/memory_resource.cc (synchronized_pool_resource::_TPools):
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Add comment about single-threaded behaviour.
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(synchronized_pool_resource::_TPools::move_nonempty_chunks()): Hoist
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class member access out of loop.
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(synchronized_pool_resource::synchronized_pool_resource())
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(synchronized_pool_resource::~synchronized_pool_resource())
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(synchronized_pool_resource::release()): Check __gthread_active_p
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before creating and/or deleting the thread-specific data key.
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(synchronized_pool_resource::_M_thread_specific_pools()): Adjust
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assertions.
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(synchronized_pool_resource::do_allocate(size_t, size_t)): Add fast
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path for single-threaded case.
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(synchronized_pool_resource::do_deallocate(void*, size_t, size_t)):
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Likewise. Return if unable to find a pool that owns the allocation.
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* testsuite/20_util/synchronized_pool_resource/allocate_single.cc:
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New test.
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* testsuite/20_util/synchronized_pool_resource/cons_single.cc: New
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test.
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* testsuite/20_util/synchronized_pool_resource/release_single.cc: New
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test.
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2020-05-03 Jonathan Wakely <jwakely@redhat.com>
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PR libstdc++/94933
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@ -1043,7 +1043,8 @@ namespace pmr
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* exposition as _M_tpools[_M_key]).
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* The first element, _M_tpools[0], contains "orphaned chunks" which were
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* allocated by a thread which has since exited, and so there is no
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* _M_tpools[_M_key] for that thread.
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* _M_tpools[_M_key] for that thread. Orphaned chunks are never reused,
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* they're only held in _M_tpools[0] so they can be deallocated.
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* A thread can access its own thread-specific set of pools via _M_key
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* while holding a shared lock on _M_mx. Accessing _M_impl._M_unpooled
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* or _M_tpools[0] or any other thread's _M_tpools[_M_key] requires an
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@ -1052,6 +1053,10 @@ namespace pmr
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* any dereference of that pointer requires an exclusive lock.
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* The _M_impl._M_opts and _M_impl._M_npools members are immutable,
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* and can safely be accessed concurrently.
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*
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* In a single-threaded program (i.e. __gthread_active_p() == false)
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* the pool resource only needs one set of pools and never has orphaned
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* chunks, so just uses _M_tpools[0] directly, and _M_tpools->next is null.
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*/
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extern "C" {
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@ -1092,14 +1097,16 @@ namespace pmr
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void move_nonempty_chunks()
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{
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__glibcxx_assert(pools);
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__glibcxx_assert(__gthread_active_p());
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if (!pools)
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return;
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memory_resource* r = owner.upstream_resource();
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memory_resource* const r = owner.upstream_resource();
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auto* const shared = owner._M_tpools->pools;
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// move all non-empty chunks to the shared _TPools
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for (int i = 0; i < owner._M_impl._M_npools; ++i)
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for (auto& c : pools[i]._M_chunks)
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if (!c.empty())
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owner._M_tpools->pools[i]._M_chunks.insert(std::move(c), r);
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shared[i]._M_chunks.insert(std::move(c), r);
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}
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synchronized_pool_resource& owner;
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@ -1133,8 +1140,9 @@ namespace pmr
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memory_resource* upstream)
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: _M_impl(opts, upstream)
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{
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if (int err = __gthread_key_create(&_M_key, destroy_TPools))
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__throw_system_error(err);
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if (__gthread_active_p())
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if (int err = __gthread_key_create(&_M_key, destroy_TPools))
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__throw_system_error(err);
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exclusive_lock l(_M_mx);
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_M_tpools = _M_alloc_shared_tpools(l);
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}
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@ -1143,7 +1151,8 @@ namespace pmr
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synchronized_pool_resource::~synchronized_pool_resource()
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{
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release();
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__gthread_key_delete(_M_key); // does not run destroy_TPools
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if (__gthread_active_p())
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__gthread_key_delete(_M_key); // does not run destroy_TPools
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}
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void
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@ -1152,8 +1161,11 @@ namespace pmr
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exclusive_lock l(_M_mx);
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if (_M_tpools)
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{
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__gthread_key_delete(_M_key); // does not run destroy_TPools
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__gthread_key_create(&_M_key, destroy_TPools);
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if (__gthread_active_p())
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{
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__gthread_key_delete(_M_key); // does not run destroy_TPools
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__gthread_key_create(&_M_key, destroy_TPools);
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}
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polymorphic_allocator<_TPools> a(upstream_resource());
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// destroy+deallocate each _TPools
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do
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@ -1175,10 +1187,11 @@ namespace pmr
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synchronized_pool_resource::_M_thread_specific_pools() noexcept
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{
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__pool_resource::_Pool* pools = nullptr;
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__glibcxx_assert(__gthread_active_p());
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if (auto tp = static_cast<_TPools*>(__gthread_getspecific(_M_key)))
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{
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pools = tp->pools;
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__glibcxx_assert(tp->pools);
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pools = tp->pools;
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// __glibcxx_assert(tp->pools);
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}
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return pools;
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}
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@ -1189,24 +1202,34 @@ namespace pmr
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do_allocate(size_t bytes, size_t alignment)
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{
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const auto block_size = std::max(bytes, alignment);
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if (block_size <= _M_impl._M_opts.largest_required_pool_block)
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const pool_options opts = _M_impl._M_opts;
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if (block_size <= opts.largest_required_pool_block)
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{
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const ptrdiff_t index = pool_index(block_size, _M_impl._M_npools);
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memory_resource* const r = upstream_resource();
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const pool_options opts = _M_impl._M_opts;
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{
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// Try to allocate from the thread-specific pool
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shared_lock l(_M_mx);
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if (auto pools = _M_thread_specific_pools()) // [[likely]]
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{
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// Need exclusive lock to replenish so use try_allocate:
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if (void* p = pools[index].try_allocate())
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return p;
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// Need to take exclusive lock and replenish pool.
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}
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// Need to allocate or replenish thread-specific pools using
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// upstream resource, so need to hold exclusive lock.
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}
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if (__gthread_active_p())
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{
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// Try to allocate from the thread-specific pool.
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shared_lock l(_M_mx);
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if (auto pools = _M_thread_specific_pools()) // [[likely]]
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{
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// Need exclusive lock to replenish so use try_allocate:
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if (void* p = pools[index].try_allocate())
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return p;
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// Need to take exclusive lock and replenish pool.
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}
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// Need to allocate or replenish thread-specific pools using
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// upstream resource, so need to hold exclusive lock.
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}
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else // single-threaded
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{
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if (!_M_tpools) // [[unlikely]]
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{
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exclusive_lock dummy(_M_mx);
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_M_tpools = _M_alloc_shared_tpools(dummy);
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}
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return _M_tpools->pools[index].allocate(upstream_resource(), opts);
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}
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// N.B. Another thread could call release() now lock is not held.
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exclusive_lock excl(_M_mx);
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if (!_M_tpools) // [[unlikely]]
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@ -1214,7 +1237,7 @@ namespace pmr
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auto pools = _M_thread_specific_pools();
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if (!pools)
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pools = _M_alloc_tpools(excl)->pools;
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return pools[index].allocate(r, opts);
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return pools[index].allocate(upstream_resource(), opts);
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}
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exclusive_lock l(_M_mx);
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return _M_impl.allocate(bytes, alignment); // unpooled allocation
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@ -1230,30 +1253,45 @@ namespace pmr
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{
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const ptrdiff_t index = pool_index(block_size, _M_impl._M_npools);
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__glibcxx_assert(index != -1);
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{
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shared_lock l(_M_mx);
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auto pools = _M_thread_specific_pools();
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if (pools)
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{
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// No need to lock here, no other thread is accessing this pool.
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if (pools[index].deallocate(upstream_resource(), p))
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return;
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}
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// Block might have come from a different thread's pool,
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// take exclusive lock and check every pool.
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}
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if (__gthread_active_p())
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{
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shared_lock l(_M_mx);
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if (auto pools = _M_thread_specific_pools())
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{
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// No need to lock here, no other thread is accessing this pool.
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if (pools[index].deallocate(upstream_resource(), p))
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return;
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}
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// Block might have come from a different thread's pool,
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// take exclusive lock and check every pool.
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}
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else // single-threaded
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{
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__glibcxx_assert(_M_tpools != nullptr);
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if (_M_tpools) // [[likely]]
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_M_tpools->pools[index].deallocate(upstream_resource(), p);
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return;
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}
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// TODO store {p, bytes, alignment} somewhere and defer returning
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// the block to the correct thread-specific pool until we next
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// take the exclusive lock.
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exclusive_lock excl(_M_mx);
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auto my_pools = _M_thread_specific_pools();
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for (_TPools* t = _M_tpools; t != nullptr; t = t->next)
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{
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if (t->pools) // [[likely]]
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{
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if (t->pools[index].deallocate(upstream_resource(), p))
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return;
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}
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if (t->pools != my_pools)
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if (t->pools) // [[likely]]
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{
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if (t->pools[index].deallocate(upstream_resource(), p))
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return;
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}
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}
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// Not necessarily an error to reach here, release() could have been
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// called on another thread between releasing the shared lock and
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// acquiring the exclusive lock.
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return;
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}
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exclusive_lock l(_M_mx);
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_M_impl.deallocate(p, bytes, alignment);
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@ -1265,6 +1303,7 @@ namespace pmr
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-> _TPools*
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{
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__glibcxx_assert(_M_tpools != nullptr);
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__glibcxx_assert(__gthread_active_p());
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// dump_list(_M_tpools);
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polymorphic_allocator<_TPools> a(upstream_resource());
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_TPools* p = a.allocate(1);
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@ -0,0 +1,24 @@
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// Copyright (C) 2018-2020 Free Software Foundation, Inc.
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//
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// This file is part of the GNU ISO C++ Library. This library is free
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// software; you can redistribute it and/or modify it under the
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// terms of the GNU General Public License as published by the
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// Free Software Foundation; either version 3, or (at your option)
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// any later version.
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// This library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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// You should have received a copy of the GNU General Public License along
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// with this library; see the file COPYING3. If not see
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// <http://www.gnu.org/licenses/>.
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// { dg-do run }
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// { dg-options "-std=gnu++17" }
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// { dg-require-effective-target c++17 }
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// { dg-require-gthreads "" }
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// This runs the same tests as allocate.cc but without -pthread
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#include "./allocate.cc"
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// Copyright (C) 2018-2020 Free Software Foundation, Inc.
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//
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// This file is part of the GNU ISO C++ Library. This library is free
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// software; you can redistribute it and/or modify it under the
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// terms of the GNU General Public License as published by the
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// Free Software Foundation; either version 3, or (at your option)
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// any later version.
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// This library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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// You should have received a copy of the GNU General Public License along
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// with this library; see the file COPYING3. If not see
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// <http://www.gnu.org/licenses/>.
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// { dg-do run }
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// { dg-options "-std=gnu++17" }
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// { dg-require-effective-target c++17 }
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// { dg-require-gthreads "" }
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// This runs the same tests as cons.cc but without -pthread
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#include "./cons.cc"
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// Copyright (C) 2018-2020 Free Software Foundation, Inc.
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//
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// This file is part of the GNU ISO C++ Library. This library is free
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// software; you can redistribute it and/or modify it under the
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// terms of the GNU General Public License as published by the
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// Free Software Foundation; either version 3, or (at your option)
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// any later version.
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// This library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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// You should have received a copy of the GNU General Public License along
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// with this library; see the file COPYING3. If not see
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// <http://www.gnu.org/licenses/>.
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// { dg-do run }
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// { dg-options "-std=gnu++17" }
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// { dg-require-effective-target c++17 }
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// { dg-require-gthreads "" }
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// This runs the same tests as release.cc but without -pthread
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#include "./release.cc"
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