https://github.com/JuliaLang/julia
Tip revision: d35536bf454449e7487598bc6ecb5d305dbb597e authored by Jameson Nash on 06 January 2023, 16:45:54 UTC
incorporate gdtoa into julia
incorporate gdtoa into julia
Tip revision: d35536b
safepoint.c
// This file is a part of Julia. License is MIT: https://julialang.org/license
#include "julia.h"
#include "julia_internal.h"
#include "threading.h"
#ifndef _OS_WINDOWS_
#include <sys/mman.h>
#if defined(_OS_DARWIN_) && !defined(MAP_ANONYMOUS)
#define MAP_ANONYMOUS MAP_ANON
#endif
#endif
#include "julia_assert.h"
#ifdef __cplusplus
extern "C" {
#endif
// 0: no sigint is pending
// 1: at least one sigint is pending, only the sigint page is enabled.
// 2: at least one sigint is pending, both safepoint pages are enabled.
JL_DLLEXPORT sig_atomic_t jl_signal_pending = 0;
_Atomic(uint32_t) jl_gc_running = 0;
char *jl_safepoint_pages = NULL;
// The number of safepoints enabled on the three pages.
// The first page, is the SIGINT page, only used by the master thread.
// The second page, is the GC page for the master thread, this is where
// the `safepoint` tls pointer points to for the master thread.
// The third page is the GC page for the other threads. The thread's
// `safepoint` tls pointer points the beginning of this page + `sizeof(size_t)`
// so that both safepoint load and pending signal load falls in this page.
// The initialization of the `safepoint` pointer is done `ti_initthread`
// in `threading.c`.
uint8_t jl_safepoint_enable_cnt[3] = {0, 0, 0};
// This lock should be acquired before enabling/disabling the safepoint
// or accessing one of the following variables:
//
// * jl_gc_running
// * jl_signal_pending
// * jl_safepoint_enable_cnt
//
// Additionally accessing `jl_gc_running` should use acquire/release
// load/store so that threads waiting for the GC doesn't have to also
// fight on the safepoint lock...
uv_mutex_t safepoint_lock;
uv_cond_t safepoint_cond;
static void jl_safepoint_enable(int idx) JL_NOTSAFEPOINT
{
// safepoint_lock should be held
assert(0 <= idx && idx < 3);
if (jl_safepoint_enable_cnt[idx]++ != 0) {
// We expect this to be enabled at most twice
// one for the GC, one for SIGINT.
// Update this if this is not the case anymore in the future.
assert(jl_safepoint_enable_cnt[idx] <= 2);
return;
}
// Now that we are requested to mprotect the page and it wasn't already.
char *pageaddr = jl_safepoint_pages + jl_page_size * idx;
#ifdef _OS_WINDOWS_
DWORD old_prot;
VirtualProtect(pageaddr, jl_page_size, PAGE_NOACCESS, &old_prot);
#else
mprotect(pageaddr, jl_page_size, PROT_NONE);
#endif
}
static void jl_safepoint_disable(int idx) JL_NOTSAFEPOINT
{
// safepoint_lock should be held
assert(0 <= idx && idx < 3);
if (--jl_safepoint_enable_cnt[idx] != 0) {
assert(jl_safepoint_enable_cnt[idx] > 0);
return;
}
// Now that we are requested to un-mprotect the page and no one else
// want it to be kept protected.
char *pageaddr = jl_safepoint_pages + jl_page_size * idx;
#ifdef _OS_WINDOWS_
DWORD old_prot;
VirtualProtect(pageaddr, jl_page_size, PAGE_READONLY, &old_prot);
#else
mprotect(pageaddr, jl_page_size, PROT_READ);
#endif
}
void jl_safepoint_init(void)
{
uv_mutex_init(&safepoint_lock);
uv_cond_init(&safepoint_cond);
// jl_page_size isn't available yet.
size_t pgsz = jl_getpagesize();
#ifdef _OS_WINDOWS_
char *addr = (char*)VirtualAlloc(NULL, pgsz * 3, MEM_COMMIT, PAGE_READONLY);
#else
char *addr = (char*)mmap(0, pgsz * 3, PROT_READ,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
if (addr == MAP_FAILED)
addr = NULL;
#endif
if (addr == NULL) {
jl_printf(JL_STDERR, "could not allocate GC synchronization page\n");
jl_gc_debug_critical_error();
abort();
}
// The signal page is for the gc safepoint.
// The page before it is the sigint pending flag.
jl_safepoint_pages = addr;
}
int jl_safepoint_start_gc(void)
{
// The thread should have set this already
assert(jl_atomic_load_relaxed(&jl_current_task->ptls->gc_state) == JL_GC_STATE_WAITING);
uv_mutex_lock(&safepoint_lock);
// In case multiple threads enter the GC at the same time, only allow
// one of them to actually run the collection. We can't just let the
// master thread do the GC since it might be running unmanaged code
// and can take arbitrarily long time before hitting a safe point.
uint32_t running = 0;
if (!jl_atomic_cmpswap(&jl_gc_running, &running, 1)) {
uv_mutex_unlock(&safepoint_lock);
jl_safepoint_wait_gc();
return 0;
}
jl_safepoint_enable(1);
jl_safepoint_enable(2);
uv_mutex_unlock(&safepoint_lock);
return 1;
}
void jl_safepoint_end_gc(void)
{
assert(jl_atomic_load_relaxed(&jl_gc_running));
uv_mutex_lock(&safepoint_lock);
// Need to reset the page protection before resetting the flag since
// the thread will trigger a segfault immediately after returning from
// the signal handler.
jl_safepoint_disable(2);
jl_safepoint_disable(1);
jl_atomic_store_release(&jl_gc_running, 0);
# ifdef __APPLE__
// This wakes up other threads on mac.
jl_mach_gc_end();
# endif
uv_mutex_unlock(&safepoint_lock);
uv_cond_broadcast(&safepoint_cond);
}
void jl_safepoint_wait_gc(void)
{
// The thread should have set this is already
assert(jl_atomic_load_relaxed(&jl_current_task->ptls->gc_state) != 0);
// Use normal volatile load in the loop for speed until GC finishes.
// Then use an acquire load to make sure the GC result is visible on this thread.
while (jl_atomic_load_relaxed(&jl_gc_running) || jl_atomic_load_acquire(&jl_gc_running)) {
// Use system mutexes rather than spin locking to minimize wasted CPU
// time on the idle cores while we wait for the GC to finish.
// This is particularly important when run under rr.
uv_mutex_lock(&safepoint_lock);
if (jl_atomic_load_relaxed(&jl_gc_running))
uv_cond_wait(&safepoint_cond, &safepoint_lock);
uv_mutex_unlock(&safepoint_lock);
}
}
void jl_safepoint_enable_sigint(void)
{
uv_mutex_lock(&safepoint_lock);
// Make sure both safepoints are enabled exactly once for SIGINT.
switch (jl_signal_pending) {
default:
assert(0 && "Shouldn't happen.");
case 0:
// Enable SIGINT page
jl_safepoint_enable(0);
// fall through
case 1:
// SIGINT page is enabled, enable GC page
jl_safepoint_enable(1);
// fall through
case 2:
jl_signal_pending = 2;
}
uv_mutex_unlock(&safepoint_lock);
}
void jl_safepoint_defer_sigint(void)
{
uv_mutex_lock(&safepoint_lock);
// Make sure the GC safepoint is disabled for SIGINT.
if (jl_signal_pending == 2) {
jl_safepoint_disable(1);
jl_signal_pending = 1;
}
uv_mutex_unlock(&safepoint_lock);
}
int jl_safepoint_consume_sigint(void)
{
int has_signal = 0;
uv_mutex_lock(&safepoint_lock);
// Make sure both safepoints are disabled for SIGINT.
switch (jl_signal_pending) {
default:
assert(0 && "Shouldn't happen.");
case 2:
// Disable gc page
jl_safepoint_disable(1);
// fall through
case 1:
// GC page is disabled, disable SIGINT page
jl_safepoint_disable(0);
has_signal = 1;
// fall through
case 0:
jl_signal_pending = 0;
}
uv_mutex_unlock(&safepoint_lock);
return has_signal;
}
#ifdef __cplusplus
}
#endif