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Utilize bitshifts correctly in signals-mach.c when storing/reading the previous GC state #53868

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merged 2 commits into from
Mar 28, 2024
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Utilize bitshifts correctly in signals-mach.c when storing/reading the previous GC state #53868

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Utilize bitshifts correctly in signals-mach.c when storing/reading th…
gbaraldi Mar 26, 2024
4c5c6f5
Utilize bitshifts correctly in signals-mach.c when storing/reading th…
gbaraldi Mar 28, 2024
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28 changes: 23 additions & 5 deletions src/signals-mach.c
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,7 @@
#include <mach/task.h>
#include <mach/mig_errors.h>
#include <AvailabilityMacros.h>
#include <stdint.h>
#include "mach_excServer.c"

#ifdef MAC_OS_X_VERSION_10_9
Expand Down Expand Up @@ -47,14 +48,31 @@ static arraylist_t suspended_threads;
extern uv_mutex_t safepoint_lock;
extern uv_cond_t safepoint_cond_begin;

#define GC_STATE_SHIFT 8*sizeof(int16_t)
static inline int8_t decode_gc_state(uintptr_t item)
{
return (int8_t)(item >> GC_STATE_SHIFT);
}

static inline int16_t decode_tid(uintptr_t item)
{
return (int16_t)item;
}

static inline uintptr_t encode_item(int16_t tid, int8_t gc_state)
{
return (uintptr_t)tid | ((uintptr_t)gc_state << GC_STATE_SHIFT);
}

// see jl_safepoint_wait_thread_resume
void jl_safepoint_resume_thread_mach(jl_ptls_t ptls2, int16_t tid2)
{
// must be called with uv_mutex_lock(&safepoint_lock) and uv_mutex_lock(&ptls2->sleep_lock) held (in that order)
for (size_t i = 0; i < suspended_threads.len; i++) {
uintptr_t item = (uintptr_t)suspended_threads.items[i];
int16_t tid = (int16_t)item;
int8_t gc_state = (int8_t)(item >> 8);

int16_t tid = decode_tid(item);
int8_t gc_state = decode_gc_state(item);
if (tid != tid2)
continue;
jl_atomic_store_release(&ptls2->gc_state, gc_state);
Expand All @@ -71,8 +89,8 @@ void jl_mach_gc_end(void)
size_t j = 0;
for (size_t i = 0; i < suspended_threads.len; i++) {
uintptr_t item = (uintptr_t)suspended_threads.items[i];
int16_t tid = (int16_t)item;
int8_t gc_state = (int8_t)(item >> 8);
int16_t tid = decode_tid(item);
int8_t gc_state = decode_gc_state(item);
jl_ptls_t ptls2 = jl_atomic_load_relaxed(&jl_all_tls_states)[tid];
uv_mutex_lock(&ptls2->sleep_lock);
if (jl_atomic_load_relaxed(&ptls2->suspend_count) == 0) {
Expand Down Expand Up @@ -117,7 +135,7 @@ static void jl_mach_gc_wait(jl_ptls_t ptls2, mach_port_t thread, int16_t tid)
// triggers a SIGSEGV and gets handled by the usual codepath for unix.
int8_t gc_state = jl_atomic_load_acquire(&ptls2->gc_state);
jl_atomic_store_release(&ptls2->gc_state, JL_GC_STATE_WAITING);
uintptr_t item = tid | (((uintptr_t)gc_state) << 16);
uintptr_t item = encode_item(tid, gc_state);
arraylist_push(&suspended_threads, (void*)item);
thread_suspend(thread);
}
Expand Down
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