[libc++] Use Fuchsia futex operations #133571
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@llvm/pr-subscribers-libcxx Author: Roland McGrath (frobtech) ChangesThe basic futex operations have always been available on Fuchsia. Full diff: https://github.com/llvm/llvm-project/pull/133571.diff 3 Files Affected:
diff --git a/libcxx/include/__atomic/contention_t.h b/libcxx/include/__atomic/contention_t.h
index 5b42a0125f875..cd3a8e4b29094 100644
--- a/libcxx/include/__atomic/contention_t.h
+++ b/libcxx/include/__atomic/contention_t.h
@@ -19,7 +19,7 @@
_LIBCPP_BEGIN_NAMESPACE_STD
-#if defined(__linux__) || (defined(_AIX) && !defined(__64BIT__))
+#if defined(__linux__) || defined(__Fuchsia__) || (defined(_AIX) && !defined(__64BIT__))
using __cxx_contention_t _LIBCPP_NODEBUG = int32_t;
#else
using __cxx_contention_t _LIBCPP_NODEBUG = int64_t;
diff --git a/libcxx/include/__cxx03/__atomic/contention_t.h b/libcxx/include/__cxx03/__atomic/contention_t.h
index a97f0668da2fe..3fc3ccef78df5 100644
--- a/libcxx/include/__cxx03/__atomic/contention_t.h
+++ b/libcxx/include/__cxx03/__atomic/contention_t.h
@@ -19,7 +19,7 @@
_LIBCPP_BEGIN_NAMESPACE_STD
-#if defined(__linux__) || (defined(_AIX) && !defined(__64BIT__))
+#if defined(__linux__) || defined(__Fuchsia__) || (defined(_AIX) && !defined(__64BIT__))
using __cxx_contention_t = int32_t;
#else
using __cxx_contention_t = int64_t;
diff --git a/libcxx/src/atomic.cpp b/libcxx/src/atomic.cpp
index c1af8d6f95aae..6de355b534b08 100644
--- a/libcxx/src/atomic.cpp
+++ b/libcxx/src/atomic.cpp
@@ -41,6 +41,10 @@
// OpenBSD has no indirect syscalls
# define _LIBCPP_FUTEX(...) futex(__VA_ARGS__)
+#elif defined(__Fuchsia__)
+
+# include <zircon/syscalls.h>
+
#else // <- Add other operating systems here
// Baseline needs no new headers
@@ -101,6 +105,24 @@ static void __libcpp_platform_wake_by_address(__cxx_atomic_contention_t const vo
_umtx_op(const_cast<__cxx_atomic_contention_t*>(__ptr), UMTX_OP_WAKE, __notify_one ? 1 : INT_MAX, nullptr, nullptr);
}
+#elif defined(__Fuchsia__)
+
+static inline zx_futex_t const* __libcpp_zx_futex(__cxx_atomic_contention_t const volatile* ptr) {
+ // Implicitly link against the vDSO system call ABI without requiring the
+ // final link to specify -lzircon explicitly when statically linking libc++.
+# pragma comment(lib, "zircon")
+ return const_cast<zx_futex_t const*>(reinterpret_cast<zx_futex_t const volatile*>(&ptr->__a_value));
+}
+
+static void
+__libcpp_platform_wait_on_address(__cxx_atomic_contention_t const volatile* __ptr, __cxx_contention_t __val) {
+ _zx_futex_wait(__libcpp_zx_futex(__ptr), __val, ZX_HANDLE_INVALID, ZX_TIME_INFINITE);
+}
+
+static void __libcpp_platform_wake_by_address(__cxx_atomic_contention_t const volatile* __ptr, bool __notify_one) {
+ _zx_futex_wake(__libcpp_zx_futex(__ptr), __notify_one ? 1 : UINT32_MAX);
+}
+
#else // <- Add other operating systems here
// Baseline is just a timed backoff
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| _LIBCPP_BEGIN_NAMESPACE_STD | ||
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| #if defined(__linux__) || (defined(_AIX) && !defined(__64BIT__)) | ||
| #if defined(__linux__) || defined(__Fuchsia__) || (defined(_AIX) && !defined(__64BIT__)) |
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Please don't modify the C++03 headers for now.
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I think it's fine now. The large refactorings have been done and I don't think I'll touch contention_t.h.
| _LIBCPP_BEGIN_NAMESPACE_STD | ||
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| #if defined(__linux__) || (defined(_AIX) && !defined(__64BIT__)) | ||
| #if defined(__linux__) || defined(__Fuchsia__) || (defined(_AIX) && !defined(__64BIT__)) |
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Might be bit unfortunate, but isn’t this an ABI break for your platform ?
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That's not really an issue on Fuchsia.
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| #elif defined(__Fuchsia__) | ||
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| static inline zx_futex_t const* __libcpp_zx_futex(__cxx_atomic_contention_t const volatile* ptr) { |
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| static inline zx_futex_t const* __libcpp_zx_futex(__cxx_atomic_contention_t const volatile* ptr) { | |
| static inline zx_futex_t const* __get_zx_futex(__cxx_atomic_contention_t const volatile* ptr) { |
Let's move away from __libcpp_ prefixes everywhere. I know it's confusing because we have a lot of them, but they shouldn't exist in most cases.
| _LIBCPP_BEGIN_NAMESPACE_STD | ||
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| #if defined(__linux__) || (defined(_AIX) && !defined(__64BIT__)) | ||
| #if defined(__linux__) || defined(__Fuchsia__) || (defined(_AIX) && !defined(__64BIT__)) |
@
@petrhosek let me know your plan. There will be some merge conflicts. My patch basically allow more types to going directly to the platform api under the unstable ABI |
6 participants
The basic futex operations have always been available on Fuchsia.
Wire them up to properly support C++20 atomic notify_*/wait.