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Runtime: emulate TLS with a map for WASI target #31694

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Runtime: emulate TLS with a map for WASI target #31694

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5 changes: 4 additions & 1 deletion stdlib/public/runtime/ThreadLocalStorage.h
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Original file line number Diff line number Diff line change
Expand Up @@ -90,7 +90,10 @@ static_assert(std::is_same<__swift_thread_key_t, DWORD>::value,
# define SWIFT_THREAD_KEY_CREATE _stdlib_thread_key_create
# define SWIFT_THREAD_GETSPECIFIC FlsGetValue
# define SWIFT_THREAD_SETSPECIFIC(key, value) (FlsSetValue(key, value) == FALSE)

# elif defined(__wasi__)
# define SWIFT_THREAD_KEY_CREATE _stdlib_thread_key_create
# define SWIFT_THREAD_GETSPECIFIC _stdlib_thread_getspecific
# define SWIFT_THREAD_SETSPECIFIC _stdlib_thread_setspecific
# else
// Otherwise use the pthread API.
# include <pthread.h>
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38 changes: 38 additions & 0 deletions stdlib/public/stubs/ThreadLocalStorage.cpp
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Expand Up @@ -54,6 +54,44 @@ _stdlib_thread_key_create(__swift_thread_key_t * _Nonnull key,

#endif

#if defined(__wasi__)
// WebAssembly doesn't have threading standardized yet, so TLS is emulated
// here, see https://bugs.swift.org/browse/SR-12774.
#include <map>
using __swift_thread_key_destructor = void (*)(void *);

struct _stdlib_tls_element_t {
const void *value;
__swift_thread_key_destructor destructor;
};

using _stdlib_tls_map_t = std::map<__swift_thread_key_t, _stdlib_tls_element_t>;
static void *_stdlib_tls_map;

static inline int _stdlib_thread_key_create(__swift_thread_key_t *key,
__swift_thread_key_destructor destructor) {
if (!_stdlib_tls_map)
_stdlib_tls_map = new _stdlib_tls_map_t();
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Suggested change
_stdlib_tls_map = new _stdlib_tls_map_t();
_stdlib_tls_map = new _stdlib_tls_map_t();

Nit: if still pursuing this PR, would you mind running the changes through the clang-format tool?

auto *map = (_stdlib_tls_map_t *)_stdlib_tls_map;
*key = map->size();
_stdlib_tls_element_t element = { nullptr, destructor };
map->insert(std::make_pair(*key, element));
return 0;
}

static inline void *_stdlib_thread_getspecific(__swift_thread_key_t key) {
auto *map = (_stdlib_tls_map_t *)_stdlib_tls_map;
return const_cast<void *>(map->operator[](key).value);
}

static inline int _stdlib_thread_setspecific(__swift_thread_key_t key, const void *value) {
auto *map = (_stdlib_tls_map_t *)_stdlib_tls_map;
map->operator[](key).value = value;
return 0;
}

#endif

#if SWIFT_TLS_HAS_RESERVED_PTHREAD_SPECIFIC

SWIFT_RUNTIME_STDLIB_INTERNAL
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