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Zero-initialize pthread struct only in debug builds. NFC #26857

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Merged
sbc100 merged 2 commits into from
May 10, 2026
+15 −11
Merged

Zero-initialize pthread struct only in debug builds. NFC #26857

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8623e10
Zero-initialize pthread struct only in debug builds. NFC
kleisauke Feb 27, 2021
879bd13
Automatic rebaseline of codesize expectations. NFC
kleisauke May 10, 2026
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8 changes: 7 additions & 1 deletion system/lib/pthread/pthread_create.c
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Original file line number Diff line number Diff line change
Expand Up @@ -279,14 +279,20 @@ void _emscripten_thread_free_data(pthread_t t) {
emscripten_builtin_free(t->profilerBlock);
}
#endif
// Clear the self-reference to prevent inadvertent use and
// inform functions that validate it that the thread is no
// longer available.
t->self = NULL;

// Free all the entire thread block (called map_base because
// Free the entire thread block (called map_base because
// musl normally allocates this using mmap). This region
// includes the pthread structure itself.
unsigned char* block = t->map_base;
dbg("_emscripten_thread_free_data thread=%p map_base=%p", t, block);
#ifndef NDEBUG
// To aid in debugging, set the entire region to zero.
memset(block, 0, sizeof(struct pthread));
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@sbc100 sbc100 May 5, 2026

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Is it not useful for debugging to reset this memory to something ? Maybe 0xfe ? Maybe only in debug builds?

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@kleisauke kleisauke May 6, 2026

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Commit e206e45 does this only for debug builds.

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@sbc100 sbc100 May 7, 2026

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Should we actually use 0xdd (or some other recognizable value) rather than zero?

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@kleisauke kleisauke May 7, 2026

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I'm not sure, but I think that would break the ->tid check in _emscripten_thread_is_valid().

#endif
emscripten_builtin_free(block);
}

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9 changes: 4 additions & 5 deletions test/codesize/test_codesize_minimal_pthreads.json
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Original file line number Diff line number Diff line change
@@ -1,10 +1,10 @@
{
"a.out.js": 7372,
"a.out.js.gz": 3593,
"a.out.nodebug.wasm": 19047,
"a.out.nodebug.wasm.gz": 8796,
"total": 26419,
"total_gz": 12389,
"a.out.nodebug.wasm": 19037,
"a.out.nodebug.wasm.gz": 8786,
"total": 26409,
"total_gz": 12379,
"sent": [
"a (memory)",
"b (exit)",
Expand Down Expand Up @@ -62,7 +62,6 @@
"funcs": [
"$__errno_location",
"$__memcpy",
"$__memset",
"$__pthread_getspecific",
"$__pthread_mutex_lock",
"$__pthread_mutex_trylock",
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9 changes: 4 additions & 5 deletions test/codesize/test_codesize_minimal_pthreads_memgrowth.json
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Original file line number Diff line number Diff line change
@@ -1,10 +1,10 @@
{
"a.out.js": 7781,
"a.out.js.gz": 3797,
"a.out.nodebug.wasm": 19048,
"a.out.nodebug.wasm.gz": 8797,
"total": 26829,
"total_gz": 12594,
"a.out.nodebug.wasm": 19038,
"a.out.nodebug.wasm.gz": 8787,
"total": 26819,
"total_gz": 12584,
"sent": [
"a (memory)",
"b (exit)",
Expand Down Expand Up @@ -62,7 +62,6 @@
"funcs": [
"$__errno_location",
"$__memcpy",
"$__memset",
"$__pthread_getspecific",
"$__pthread_mutex_lock",
"$__pthread_mutex_trylock",
Expand Down
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