Merge pull request #50083 from topolarity/fasttls-semaphore

Prevent registering static FASTTLS with multiple libjulias
JuliaLang · Jun 13, 2023 · 84fc130 · 84fc130
2 parents 9d839f9 + 97f445e
commit 84fc130
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Showing 2 changed files with 15 additions and 2 deletions.
diff --git a/cli/loader_lib.c b/cli/loader_lib.c
@@ -527,8 +527,13 @@ __attribute__((constructor)) void jl_load_libjulia_internal(void) {
     }
     void *fptr = lookup_symbol(RTLD_DEFAULT, "jl_get_pgcstack_static");
     void *(*key)(void) = lookup_symbol(RTLD_DEFAULT, "jl_pgcstack_addr_static");
-    if (fptr != NULL && key != NULL)
-        jl_pgcstack_setkey(fptr, key);
+    _Atomic(char) *semaphore = lookup_symbol(RTLD_DEFAULT, "jl_pgcstack_static_semaphore");
+    if (fptr != NULL && key != NULL && semaphore != NULL) {
+        char already_used = 0;
+        atomic_compare_exchange_strong(semaphore, &already_used, 1);
+        if (already_used == 0) // RMW succeeded - we have exclusive access
+            jl_pgcstack_setkey(fptr, key);
+    }
 #endif
 
     // jl_options must be initialized very early, in case an embedder sets some

diff --git a/src/julia_fasttls.h b/src/julia_fasttls.h
@@ -3,6 +3,13 @@
 #ifndef JL_FASTTLS_H
 #define JL_FASTTLS_H
 
+#ifdef __cplusplus
+#include <atomic>
+#define _Atomic(T) std::atomic<T>
+#else
+#include <stdatomic.h>
+#endif
+
 // Thread-local storage access
 
 #ifdef __cplusplus
@@ -25,6 +32,7 @@ typedef jl_gcframe_t **(jl_get_pgcstack_func)(void);
 #if !defined(_OS_DARWIN_) && !defined(_OS_WINDOWS_)
 #define JULIA_DEFINE_FAST_TLS                                                                   \
 static __attribute__((tls_model("local-exec"))) __thread jl_gcframe_t **jl_pgcstack_localexec;  \
+JL_DLLEXPORT _Atomic(char) jl_pgcstack_static_semaphore;                                        \
 JL_DLLEXPORT jl_gcframe_t **jl_get_pgcstack_static(void)                                        \
 {                                                                                               \
     return jl_pgcstack_localexec;                                                               \