[PATCH] D42742: [clangd] Use pthread instead of thread_local to support more runtimes.
Sam McCall via Phabricator via cfe-commits
cfe-commits at lists.llvm.org
Wed Jan 31 08:39:19 PST 2018
sammccall created this revision.
sammccall added reviewers: ilya-biryukov, bkramer.
Herald added subscribers: cfe-commits, ioeric, jkorous-apple, klimek.
thread_local has nice syntax and semantics, but requires __cxa_thread_atexit,
and some not-ancient runtime libraries don't provide it.
The clang-x86_64-linux-selfhost-modules buildbot is one example :-)
It works on windows, and the other platforms clang-tools-extra supports should
all have the relevant pthread API. So we just use that if it's available,
falling back to thread_local (so if a platform has neither, we'll fail to link).
The fallback should really be the other way, that would require cmake changes.
Repository:
rCTE Clang Tools Extra
https://reviews.llvm.org/D42742
Files:
clangd/Context.cpp
Index: clangd/Context.cpp
===================================================================
--- clangd/Context.cpp
+++ clangd/Context.cpp
@@ -8,8 +8,48 @@
//===---------------------------------------------------------------------===//
#include "Context.h"
+#include "llvm/Config/config.h"
#include <cassert>
+// The thread-local Context is scoped in a function to avoid init-order issues.
+// It's created by currentContext() when first needed.
+
+#ifdef HAVE_PTHREAD_GETSPECIFIC
+// We'd love to use thread_local everywhere.
+// It requires support from the runtime: __cxa_thread_atexit.
+// Rather than detect this, we use the pthread API where available.
+#include <pthread.h>
+static clang::clangd::Context ¤tContext() {
+ using clang::clangd::Context;
+ static pthread_key_t CtxKey;
+
+ // Once (across threads), set up pthread TLS for Context, and its destructor.
+ static int Dummy = [] { // Create key only once, for all threads.
+ if (auto Err = pthread_key_create(&CtxKey, /*destructor=*/+[](void *Ctx) {
+ delete reinterpret_cast<Context *>(Ctx);
+ }))
+ llvm_unreachable(strerror(Err));
+ return 0;
+ }();
+ (void)Dummy;
+
+ // Now grab the current context from TLS, and create it if it doesn't exist.
+ void *Ctx = pthread_getspecific(CtxKey);
+ if (!Ctx) {
+ Ctx = new Context();
+ if (auto Err = pthread_setspecific(CtxKey, Ctx))
+ llvm_unreachable(strerror(Err));
+ }
+ return *reinterpret_cast<Context *>(Ctx);
+}
+#else
+// Only supported platform without pthread is windows, and thread_local works.
+static clang::clangd::Context ¤tContext() {
+ static thread_local auto C = clang::clangd::Context::empty();
+ return C;
+}
+#endif
+
namespace clang {
namespace clangd {
@@ -20,13 +60,6 @@
Context Context::clone() const { return Context(DataPtr); }
-// The thread-local Context is scoped in a function to avoid
-// initialization-order issues. It's created when first needed.
-static Context ¤tContext() {
- static thread_local Context C = Context::empty();
- return C;
-}
-
const Context &Context::current() { return currentContext(); }
Context Context::swapCurrent(Context Replacement) {
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