c6e466911f
Summary: In some places in libc++ we need to use the `__atomic_*` builtins. This patch adds a header that provides access to those builtins in a uniform way from within the dylib source. If the compiler building the dylib does not support these builtins then a warning is issued. Only relaxed loads are needed within the headers. A singe function to do these relaxed loads has been added to `<memory>`. This patch applies the new atomic builtins to `__shared_count` and `call_once`. Reviewers: mclow.lists Subscribers: majnemer, jroelofs, cfe-commits Differential Revision: http://reviews.llvm.org/D10406 git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@241532 91177308-0d34-0410-b5e6-96231b3b80d8
95 lines
2.5 KiB
C++
95 lines
2.5 KiB
C++
//===----------------------------------------------------------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is dual licensed under the MIT and the University of Illinois Open
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// Source Licenses. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// UNSUPPORTED: libcpp-has-no-threads
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//
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// <memory>
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//
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// class shared_ptr
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//
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// This test attempts to create a race condition surrounding use_count()
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// with the hope that TSAN will diagnose it.
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#include <memory>
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#include <atomic>
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#include <thread>
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#include <cassert>
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typedef std::shared_ptr<int> Ptr;
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typedef std::weak_ptr<int> WeakPtr;
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std::atomic_bool Start;
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std::atomic_bool KeepRunning;
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struct TestRunner {
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TestRunner(Ptr xx) : x(xx) {}
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void operator()() {
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while (Start == false) {}
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while (KeepRunning) {
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// loop to prevent always checking the atomic.
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for (int i=0; i < 100000; ++i) {
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Ptr x2 = x; // increment shared count
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WeakPtr x3 = x; // increment weak count
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Ptr x4 = x3.lock(); // increment shared count via lock
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WeakPtr x5 = x3; // increment weak count
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}
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}
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}
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Ptr x;
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};
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void run_test(Ptr p) {
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Start = false;
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KeepRunning = true;
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assert(p.use_count() == 2);
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TestRunner r(p);
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assert(p.use_count() == 3);
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std::thread t1(r); // Start the test thread.
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assert(p.use_count() == 4);
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Start = true;
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// Run until we witness 25 use count changes via both
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// shared and weak pointer methods.
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WeakPtr w = p;
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int shared_changes_count = 0;
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int weak_changes_count = 0;
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while (shared_changes_count < 25 && weak_changes_count < 25) {
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// check use_count on the shared_ptr
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int last = p.use_count();
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int new_val = p.use_count();
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assert(last >= 4);
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assert(new_val >= 4);
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if (last != new_val) ++shared_changes_count;
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// Check use_count on the weak_ptr
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last = w.use_count();
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new_val = w.use_count();
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assert(last >= 4);
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assert(new_val >= 4);
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if (last != new_val) ++weak_changes_count;
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}
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// kill the test thread.
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KeepRunning = false;
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t1.join();
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assert(p.use_count() == 3);
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}
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int main() {
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{
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// Test with out-of-place shared_count.
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Ptr p(new int(42));
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run_test(p);
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assert(p.use_count() == 1);
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}
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{
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// Test with in-place shared_count.
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Ptr p = std::make_shared<int>(42);
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run_test(p);
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assert(p.use_count() == 1);
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}
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}
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