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products/Sources/formale Sprachen/GAP/src/hpc/ (Algebra von RWTH Aachen Version 4.15.1^©) Datei vom 18.9.2025 mit Größe 38 kB

SSL thread.c Sprache: C

/****************************************************************************
**
**  This file is part of GAP, a system for computational discrete algebra.
**
**  Copyright of GAP belongs to its developers, whose names are too numerous
**  to list here. Please refer to the COPYRIGHT file for details.
**
**  SPDX-License-Identifier: GPL-2.0-or-later
*/

#include "thread.h"

#include "../code.h"
#include "../error.h"
#include "../fibhash.h"
#include "../gapstate.h"
#include "../gvars.h"
#include "../modules.h"
#include "../plist.h"
#include "../stats.h"
#include "../stringobj.h"
#include "../vars.h"

#include "guards.h"
#include "misc.h"
#include "threadapi.h"

#include <errno.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <unistd.h>

#ifdef USE_BOEHM_GC
# ifdef HPCGAP
#  define GC_THREADS
# endif
# include <gc/gc.h>
#endif

#define LOG2_NUM_LOCKS 11
#define NUM_LOCKS (1 << LOG2_NUM_LOCKS)

#ifndef WARD_ENABLED

typedef struct ThreadData {
    pthread_t         pthread_id;
    pthread_mutex_t * lock;
    pthread_cond_t *  cond;
    int               joined;
    int               system;
    AtomicUInt        state;
    void *            tls;
    void (*start)(void *);
    void *              arg;
    Obj                 thread_object;
    Obj                 region_name;
    struct ThreadData * next;
} ThreadData;

Region *LimboRegion, *ReadOnlyRegion;
Obj     PublicRegionName;

static int        GlobalPauseInProgress;
static AtomicUInt ThreadCounter = 1;

static inline void IncThreadCounter(void)
{
    ATOMIC_INC(&ThreadCounter);
}

static inline void DecThreadCounter(void)
{
    ATOMIC_DEC(&ThreadCounter);
}

static ThreadData   thread_data[MAX_THREADS];
static ThreadData * paused_threads[MAX_THREADS];
static ThreadData * thread_free_list;
static int          num_paused_threads;

static pthread_rwlock_t master_lock;

static pthread_rwlock_t ObjLock[NUM_LOCKS];

int PreThreadCreation = 1;

void LockThreadControl(int modify)
{
    if (modify)
        pthread_rwlock_wrlock(&master_lock);
    else
        pthread_rwlock_rdlock(&master_lock);
}

void UnlockThreadControl(void)
{
    pthread_rwlock_unlock(&master_lock);
}

#ifndef MAP_ANONYMOUS
#define MAP_ANONYMOUS MAP_ANON
#endif

#ifndef USE_NATIVE_TLS

#ifdef USE_PTHREAD_TLS
static int InitTLSKey;
static pthread_key_t TLSKey;
#ifdef USE_MACOS_PTHREAD_TLS_ASM
static UInt TLSOffset;

// The following code also occurs in configure.ac, and both need to be
// kept in sync.

#define OFFS 0x100
#define END (-1)

int cmpOpCode(unsigned char *code, int *with) {
    int result = 0;
    while (*with >= 0) {
        if (*with == OFFS) {
            result = *code;
        } else {
            if (*code != *with)
                return -1;
        }
        code++;
        with++;
    }
    return result;
}

void FindTLSOffset() {
    // This is an idea borrowed from Mono. We test if the implementation
    // of pthread_getspecific() uses the assembly code below. If that is
    // true, we can replace calls to pthread_getspecific() with the
    // matching inline assembly, allowing a significant performance boost.
    // There are two possible implementations.
    static int asm_code[] = {
        // movq %gs:[OFFS](,%rdi,8), %rax
        // retq
        0x65, 0x48, 0x8b, 0x04, 0xfd, OFFS, 0x00, 0x00, 0x00, 0xc3, END
    };
    static int asm_code2[] = {
        // pushq  %rbp
        // movq   %rsp, %rbp
        // movq   %gs:[OFFS](,%rdi,8),%rax
        // popq   %rbp
        // retq
        0x55, 0x48, 0x89, 0xe5, 0x65, 0x48, 0x8b, 0x04, 0xfd, OFFS,
        0x00, 0x00, 0x00, 0x5d, 0xc3, END
    };
    TLSOffset = cmpOpCode((unsigned char *)pthread_getspecific, asm_code);
    if (TLSOffset >= 0)
        return;
    TLSOffset = cmpOpCode((unsigned char *)pthread_getspecific, asm_code2);
    if (TLSOffset >= 0)
        return;
    Panic("Unable to find macOS thread-local storage offset");
}
#endif

static void CreateTLSKey(void)
{
    pthread_key_create(&TLSKey, NULL);
#ifdef USE_MACOS_PTHREAD_TLS_ASM
    FindTLSOffset();
#endif
    InitTLSKey = 1;
}

#ifdef USE_MACOS_PTHREAD_TLS_ASM
UInt GetTLSOffset(void)
{
    if (!InitTLSKey) {
        CreateTLSKey();
    }
    return (UInt)TLSKey * sizeof(void *) + TLSOffset;
}
#endif
pthread_key_t GetTLSKey(void)
{
    if (!InitTLSKey) {
        CreateTLSKey();
    }
    return TLSKey;
}
#endif // USE_PTHREAD_TLS

void * AllocateTLS(void)
{
#ifndef USE_PTHREAD_TLS
    void * addr;
    void * result;
    size_t pagesize = getpagesize();
    size_t tlssize =
        (sizeof(GAPState) + pagesize - 1) & ~(pagesize - 1);
    addr = mmap(0, 2 * TLS_SIZE, PROT_READ | PROT_WRITE,
                MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
    result = (void *)((((uintptr_t)addr) + (TLS_SIZE - 1)) & TLS_MASK);
    munmap(addr, (char *)result - (char *)addr);
    munmap((char *)result + TLS_SIZE,
           (char *)addr - (char *)result + TLS_SIZE);
// generate a stack overflow protection area
#ifdef STACK_GROWS_UP
    mprotect((char *)result + TLS_SIZE - tlssize - pagesize, pagesize,
             PROT_NONE);
#else
    mprotect((char *)result + tlssize, pagesize, PROT_NONE);
#endif
    return result;
#else
    void * result = pthread_getspecific(GetTLSKey());
    if (!result) {
        result = malloc(sizeof(GAPState));
        pthread_setspecific(GetTLSKey(), result);
    }
    return result;
#endif // USE_PTHREAD_TLS
}

void FreeTLS(void * address)
{
/* We currently cannot free this memory because of garbage collector
* issues. Instead, it will be reused */
#if 0
  munmap(address, TLS_STACK_SIZE);
#endif
}

#endif // USE_NATIVE_TLS

#ifndef DISABLE_GC
void AddGCRoots(void)
{
    void * p = ActiveGAPState();
    GC_add_roots(p, (char *)p + sizeof(GAPState));
}

static void RemoveGCRoots(void)
{
    void * p = ActiveGAPState();
#if defined(__CYGWIN__) || defined(__CYGWIN32__)
    memset(p, '\0', sizeof(GAPState));
#else
    GC_remove_roots(p, (char *)p + sizeof(GAPState));
#endif
}
#endif // DISABLE_GC

#if !defined(USE_NATIVE_TLS) && !defined(USE_PTHREAD_TLS)

/* In order to safely use thread-local memory on the main stack, we have
* to work around an idiosyncrasy in some virtual memory systems. These
* VM implementations do not allow fully random access within the stack
* segment, but only quasi-linear access: a page can only be accessed if
* a nearby page was accessed before. If this pattern is not observed,
* but if we access memory within the stack segment randomly -- as in
* our TLS implementation, but also with very large stack frames -- a
* segmentation fault can arise. To avoid such segmentation faults, we
* traverse the stack segment of the main stack, touching each page in
* turn.
*
* Note that this is not necessary for thread stacks, which are
* allocated in private memory-mapped storage.
*/

static NOINLINE void GrowStack(void)
{
    char * tls = (char *)GetTLS();
    size_t pagesize = getpagesize();
    /* p needs to be a volatile pointer so that the memory writes are not
     * removed by the optimizer */
    volatile char * p = alloca(pagesize);
    while (p > tls) {
        // touch memory
        *p = '\0';
        p = alloca(pagesize);
    }
}
#endif

static NOINLINE void SetupTLS(void)
{
#if !defined(USE_NATIVE_TLS) && !defined(USE_PTHREAD_TLS)
    GrowStack();
#endif
    InitializeTLS();
    TLS(threadID) = 0;
}

void InitMainThread(void)
{
    TLS(threadObject) = NewThreadObject(0);
    TLS(CountActive) = 1;
}

static NOINLINE void RunThreadedMain2(int (*mainFunction)(int, const char **),
                             int     argc,
                             const char ** argv);

void RunThreadedMain(int (*mainFunction)(int, const char **),
                     int     argc,
                     const char ** argv)
{
#ifndef USE_NATIVE_TLS
#ifdef STACK_GROWS_UP
#error Upward growing stack not yet supported
#else
    /* We need to ensure that the stack pointer and frame pointer
     * of the called function begin at the top end of a memory
     * segment whose beginning and end address are a multiple of
     * TLS_SIZE (which is a power of 2). To that end, we look at
     * an approximation of the current stack pointer by taking
     * the address of a local variable, then mask out the lowest
     * bits and use alloca() to allocate at least that many bytes
     * on the stack. We also need to touch the pages in that area;
     * see the comments on GrowStack() for the reason why.
     */
    volatile int dummy[1];
    size_t       amount;
    amount = ((uintptr_t)dummy) & ~TLS_MASK;
    volatile char * p = alloca(((uintptr_t)dummy) & ~TLS_MASK);
    volatile char * q;
    for (q = p + amount - 1; (void *)q >= (void *)p; q -= 1024) {
        // touch memory
        *q = '\0';
    }
#endif
#endif
    RunThreadedMain2(mainFunction, argc, argv);
}

static void RunThreadedMain2(int (*mainFunction)(int, const char **),
                             int     argc,
                             const char ** argv)
{
    int                    i;
    static pthread_mutex_t main_thread_mutex;
    static pthread_cond_t  main_thread_cond;
    SetupTLS();
    for (i = 1; i < MAX_THREADS - 1; i++)
        thread_data[i].next = thread_data + i + 1;
    thread_data[0].next = NULL;
    for (i = 0; i < NUM_LOCKS; i++)
        pthread_rwlock_init(&ObjLock[i], 0);
    thread_data[MAX_THREADS - 1].next = NULL;
    for (i = 0; i < MAX_THREADS; i++) {
        thread_data[i].tls = 0;
        thread_data[i].state = TSTATE_TERMINATED;
        thread_data[i].system = 0;
    }
    thread_free_list = thread_data + 1;
    pthread_rwlock_init(&master_lock, 0);
    pthread_mutex_init(&main_thread_mutex, 0);
    pthread_cond_init(&main_thread_cond, 0);
    TLS(threadLock) = &main_thread_mutex;
    TLS(threadSignal) = &main_thread_cond;
    thread_data[0].lock = TLS(threadLock);
    thread_data[0].cond = TLS(threadSignal);
    thread_data[0].state = TSTATE_RUNNING;
    thread_data[0].tls = GetTLS();
    InitSignals();
    if (setjmp(TLS(threadExit)))
        exit(0);
    exit((*mainFunction)(argc, argv));
}

void CreateMainRegion(void)
{
    int i;
    TLS(currentRegion) = NewRegion();
    TLS(threadRegion) = TLS(currentRegion);
    TLS(currentRegion)->fixed_owner = 1;
    RegionWriteLock(TLS(currentRegion));
    TLS(currentRegion)->name = MakeImmString("thread region #0");
    PublicRegionName = MakeImmString("public region");
    LimboRegion = NewRegion();
    LimboRegion->fixed_owner = 1;
    LimboRegion->name = MakeImmString("limbo region");
    ReadOnlyRegion = NewRegion();
    ReadOnlyRegion->name = MakeImmString("read-only region");
    ReadOnlyRegion->fixed_owner = 1;
    for (i = 0; i <= MAX_THREADS; i++) {
        ReadOnlyRegion->readers[i] = 1;
    }
}

static Obj MakeImmString2(const Char * cstr1, const Char * cstr2)
{
    Obj    result;
    size_t len1 = strlen(cstr1), len2 = strlen(cstr2);
    result = NEW_STRING(len1 + len2);
    memcpy(CSTR_STRING(result), cstr1, len1);
    memcpy(CSTR_STRING(result) + len1, cstr2, len2);
    MakeImmutableNoRecurse(result);
    return result;
}

static void * DispatchThread(void * arg)
{
    ThreadData * this_thread = arg;
    Region *     region;
    InitializeTLS();
    TLS(threadID) = this_thread - thread_data;
#ifndef DISABLE_GC
    AddGCRoots();
#endif
    ModulesInitModuleState();
    TLS(CountActive) = 1;
    region = NewRegion();
    TLS(currentRegion) = region;
    TLS(threadRegion) = region;
    TLS(threadLock) = this_thread->lock;
    TLS(threadSignal) = this_thread->cond;
    region->fixed_owner = 1;
    region->name = this_thread->region_name;
    RegionWriteLock(region);
    if (!this_thread->region_name) {
        char buf[8];
        sprintf(buf, "%d", TLS(threadID));
        this_thread->region_name = MakeImmString2("thread #", buf);
    }
    SetRegionName(region, this_thread->region_name);
    TLS(threadObject) = this_thread->thread_object;
    pthread_mutex_lock(this_thread->lock);

    ThreadObject *thread = (ThreadObject *)ADDR_OBJ(TLS(threadObject));
    thread->tls = GetTLS();
    pthread_cond_broadcast(this_thread->cond);
    pthread_mutex_unlock(this_thread->lock);
    this_thread->start(this_thread->arg);
    thread->status |= THREAD_TERMINATED;
    region->fixed_owner = 0;
    RegionWriteUnlock(region);
    ModulesDestroyModuleState();
    memset(ActiveGAPState(), 0, sizeof(GAPState));
#ifndef DISABLE_GC
    RemoveGCRoots();
#endif
    this_thread->state = TSTATE_TERMINATED;
    DecThreadCounter();
    return 0;
}

Obj RunThread(void (*start)(void *), void * arg)
{
    ThreadData * result;
#ifndef USE_NATIVE_TLS
    void * tls;
#endif
    pthread_attr_t thread_attr;
    LockThreadControl(1);
    PreThreadCreation = 0;
    // allocate a new thread id
    if (thread_free_list == NULL) {
        UnlockThreadControl();
        errno = ENOMEM;
        return (Obj)0;
    }
    result = thread_free_list;
    thread_free_list = thread_free_list->next;
#ifndef USE_NATIVE_TLS
    if (!result->tls)
        result->tls = AllocateTLS();
    tls = result->tls;
#endif
    if (!result->lock) {
        result->lock = AllocateMemoryBlock(sizeof(pthread_mutex_t));
        result->cond = AllocateMemoryBlock(sizeof(pthread_cond_t));
        pthread_mutex_init(result->lock, 0);
        pthread_cond_init(result->cond, 0);
    }
    result->arg = arg;
    result->start = start;
    result->joined = 0;
    if (GlobalPauseInProgress) {
        // New threads will be automatically paused
        result->state = TSTATE_PAUSED;
        HandleInterrupts(0, 0);
    }
    else {
        result->state = TSTATE_RUNNING;
    }
    result->thread_object = NewThreadObject(result - thread_data);
    // set up the thread attribute to support a custom stack in our TLS
    pthread_attr_init(&thread_attr);
#if !defined(USE_NATIVE_TLS) && !defined(USE_PTHREAD_TLS)
    size_t         pagesize = getpagesize();
    pthread_attr_setstack(&thread_attr, (char *)tls + pagesize * 2,
                          TLS_SIZE - pagesize * 2);
#endif
    UnlockThreadControl();
    // fork the thread
    IncThreadCounter();
    if (pthread_create(&result->pthread_id, &thread_attr, DispatchThread,
                       result) < 0) {
        // No more threads available
        DecThreadCounter();
        LockThreadControl(1);
        result->next = thread_free_list;
        thread_free_list = result;
        UnlockThreadControl();
        pthread_attr_destroy(&thread_attr);
#ifndef USE_NATIVE_TLS
        FreeTLS(tls);
#endif
        return (Obj)0;
    }
    pthread_attr_destroy(&thread_attr);
    return result->thread_object;
}

int JoinThread(int id)
{
    pthread_t pthread_id;
    void (*start)(void *);
#ifndef USE_NATIVE_TLS
    void * tls;
#endif
    if (id < 0 || id >= MAX_THREADS)
        return 0;
    LockThreadControl(1);
    pthread_id = thread_data[id].pthread_id;
    start = thread_data[id].start;
#ifndef USE_NATIVE_TLS
    tls = thread_data[id].tls;
#endif
    if (thread_data[id].joined || start == NULL) {
        UnlockThreadControl();
        return 0;
    }
    thread_data[id].joined = 1;
    UnlockThreadControl();
    pthread_join(pthread_id, NULL);
    LockThreadControl(1);
    thread_data[id].next = thread_free_list;
    thread_free_list = thread_data + id;
    /*
    FreeTLS(thread_data[id].tls);
    thread_data[id].tls = NULL;
    */
    thread_data[id].start = NULL;
    UnlockThreadControl();
#ifndef USE_NATIVE_TLS
    FreeTLS(tls);
#endif
    return 1;
}

static UInt LockID(void * object)
{
#ifdef CUSTOM_OBJECT_HASH
    UInt p = (UInt)object;
    if (sizeof(void *) == 4)
        return ((p >> 2) ^ (p >> (2 + LOG2_NUM_LOCKS)) ^
                (p << (LOG2_NUM_LOCKS - 2))) %
               NUM_LOCKS;
    else
        return ((p >> 3) ^ (p >> (3 + LOG2_NUM_LOCKS)) ^
                (p << (LOG2_NUM_LOCKS - 3))) %
               NUM_LOCKS;
#else
    return FibHash((UInt)object, LOG2_NUM_LOCKS);
#endif
}

void HashLock(void * object)
{
    if (TLS(CurrentHashLock))
        ErrorQuit("Nested hash locks", 0, 0);
    TLS(CurrentHashLock) = object;
    pthread_rwlock_wrlock(&ObjLock[LockID(object)]);
}

void HashLockShared(void * object)
{
    if (TLS(CurrentHashLock))
        ErrorQuit("Nested hash locks", 0, 0);
    TLS(CurrentHashLock) = object;
    pthread_rwlock_rdlock(&ObjLock[LockID(object)]);
}

void HashUnlock(void * object)
{
    if (TLS(CurrentHashLock) != object)
        ErrorQuit("Improperly matched hash lock/unlock calls", 0, 0);
    TLS(CurrentHashLock) = 0;
    pthread_rwlock_unlock(&ObjLock[LockID(object)]);
}

void HashUnlockShared(void * object)
{
    if (TLS(CurrentHashLock) != object)
        ErrorQuit("Improperly matched hash lock/unlock calls", 0, 0);
    TLS(CurrentHashLock) = 0;
    pthread_rwlock_unlock(&ObjLock[LockID(object)]);
}

void RegionWriteLock(Region * region)
{
    int result = 0;
    assert(region->owner != GetTLS());

    if (region->count_active || TLS(CountActive)) {
        result = !pthread_rwlock_trywrlock(region->lock);

        if (result) {
            if (region->count_active)
                region->locks_acquired++;
            if (TLS(CountActive))
                TLS(LocksAcquired)++;
        }
        else {
            if (region->count_active)
                region->locks_contended++;
            if (TLS(CountActive))
                TLS(LocksContended)++;
            pthread_rwlock_wrlock(region->lock);
        }
    }
    else {
        pthread_rwlock_wrlock(region->lock);
    }

    region->owner = GetTLS();
}

int RegionTryWriteLock(Region * region)
{
    int result;
    assert(region->owner != GetTLS());
    result = !pthread_rwlock_trywrlock(region->lock);

    if (result) {
        if (region->count_active)
            region->locks_acquired++;
        if (TLS(CountActive))
            TLS(LocksAcquired)++;
        region->owner = GetTLS();
    }
    else {
        if (region->count_active)
            region->locks_contended++;
        if (TLS(CountActive))
            TLS(LocksContended)++;
    }
    return result;
}

void RegionWriteUnlock(Region * region)
{
    assert(region->owner == GetTLS());
    region->owner = NULL;
    pthread_rwlock_unlock(region->lock);
}

void RegionReadLock(Region * region)
{
    int result = 0;
    assert(region->owner != GetTLS());
    assert(region->readers[TLS(threadID)] == 0);

    if (region->count_active || TLS(CountActive)) {
        result = !pthread_rwlock_rdlock(region->lock);

        if (result) {
            if (region->count_active)
                ATOMIC_INC(®ion->locks_acquired);
            if (TLS(CountActive))
                TLS(LocksAcquired)++;
        }
        else {
            if (region->count_active)
                ATOMIC_INC(®ion->locks_contended);
            if (TLS(CountActive))
                TLS(LocksAcquired)++;
            pthread_rwlock_rdlock(region->lock);
        }
    }
    else {
        pthread_rwlock_rdlock(region->lock);
    }
    region->readers[TLS(threadID)] = 1;
}

int RegionTryReadLock(Region * region)
{
    int result = !pthread_rwlock_rdlock(region->lock);
    assert(region->owner != GetTLS());
    assert(region->readers[TLS(threadID)] == 0);

    if (result) {
        if (region->count_active)
            ATOMIC_INC(®ion->locks_acquired);
        if (TLS(CountActive))
            TLS(LocksAcquired)++;
        region->readers[TLS(threadID)] = 1;
    }
    else {
        if (region->count_active)
            ATOMIC_INC(®ion->locks_contended);
        if (TLS(CountActive))
            TLS(LocksContended)++;
    }
    return result;
}

void RegionReadUnlock(Region * region)
{
    assert(region->readers[TLS(threadID)]);
    region->readers[TLS(threadID)] = 0;
    pthread_rwlock_unlock(region->lock);
}

void RegionUnlock(Region * region)
{
    assert(region->owner == GetTLS() || region->readers[TLS(threadID)]);
    if (region->owner == GetTLS())
        region->owner = NULL;
    region->readers[TLS(threadID)] = 0;
    pthread_rwlock_unlock(region->lock);
}

LockStatus IsLocked(Region * region)
{
    if (!region)
        return LOCK_STATUS_UNLOCKED; // public region
    if (region->owner == GetTLS())
        return LOCK_STATUS_READWRITE_LOCKED;
    if (region->readers[TLS(threadID)])
        return LOCK_STATUS_READONLY_LOCKED;
    return LOCK_STATUS_UNLOCKED;
}

Region * GetRegionOf(Obj obj)
{
    if (!IS_BAG_REF(obj))
        return NULL;
    if (TNUM_OBJ(obj) == T_REGION)
        return *(Region **)(ADDR_OBJ(obj));
    return REGION(obj);
}

void SetRegionName(Region * region, Obj name)
{
    if (name) {
        if (!IS_STRING(name))
            return;
        if (IS_MUTABLE_OBJ(name))
            name = CopyObj(name, 0);
    }
    MEMBAR_WRITE();
    region->name = name;
}

Obj GetRegionName(Region * region)
{
    Obj result;
    if (region)
        result = region->name;
    else
        result = PublicRegionName;
    MEMBAR_READ();
    return result;
}

void GetLockStatus(int count, Obj * objects, LockStatus * status)
{
    int i;
    for (i = 0; i < count; i++)
        status[i] = IsLocked(REGION(objects[i]));
}

static Obj NewList(UInt size)
{
    Obj list;
    list = NEW_PLIST(size == 0 ? T_PLIST_EMPTY : T_PLIST, size);
    SET_LEN_PLIST(list, size);
    return list;
}

Obj GetRegionLockCounters(Region * region)
{
    Obj result = NewList(2);

    if (region) {
        SET_ELM_PLIST(result, 1, INTOBJ_INT(region->locks_acquired));
        SET_ELM_PLIST(result, 2, INTOBJ_INT(region->locks_contended));
    }
    MEMBAR_READ();
    return result;
}

void ResetRegionLockCounters(Region * region)
{
    if (region) {
        region->locks_acquired = region->locks_contended = 0;
    }
    MEMBAR_WRITE();
}

#define MAX_LOCKS 1024

typedef struct {
    Obj      obj;
    Region * region;
    LockMode mode;
} LockRequest;

static int LessThanLockRequest(const void * a, const void * b)
{
    Region * region_a = ((LockRequest *)a)->region;
    Region * region_b = ((LockRequest *)b)->region;
    Int      prec_diff;
    if (region_a == region_b) // prioritize writes
        return ((LockRequest *)a)->mode > ((LockRequest *)b)->mode;
    prec_diff = region_a->prec - region_b->prec;
    return prec_diff > 0 ||
           (prec_diff == 0 && (char *)region_a < (char *)region_b);
}

void PushRegionLock(Region * region)
{
    if (!TLS(lockStack)) {
        TLS(lockStack) = NewList(16);
        TLS(lockStackPointer) = 0;
    }
    else if (LEN_PLIST(TLS(lockStack)) == TLS(lockStackPointer)) {
        int newlen = TLS(lockStackPointer) * 3 / 2;
        GROW_PLIST(TLS(lockStack), newlen);
    }
    TLS(lockStackPointer)++;
    SET_ELM_PLIST(TLS(lockStack), TLS(lockStackPointer),
                  region ? region->obj : (Obj)0);
}

void PopRegionLocks(int newSP)
{
    while (newSP < TLS(lockStackPointer)) {
        int p = TLS(lockStackPointer)--;
        Obj region_obj = ELM_PLIST(TLS(lockStack), p);
        if (!region_obj)
            continue;
        Region * region = *(Region **)(ADDR_OBJ(region_obj));
        RegionUnlock(region);
        SET_ELM_PLIST(TLS(lockStack), p, (Obj)0);
    }
}

int RegionLockSP(void)
{
    return TLS(lockStackPointer);
}

int GetThreadState(int threadID)
{
    return (int)(thread_data[threadID].state);
}

int UpdateThreadState(int threadID, int oldState, int newState)
{
    return COMPARE_AND_SWAP(&thread_data[threadID].state,
                            (AtomicUInt)oldState, (AtomicUInt)newState);
}

static void SetInterrupt(int threadID)
{
    ThreadLocalStorage * tls = thread_data[threadID].tls;
    MEMBAR_FULL();
    ((GAPState *)tls)->CurrExecStatFuncs = IntrExecStatFuncs;
}

static int LockAndUpdateThreadState(int threadID, int oldState, int newState)
{
    if (pthread_mutex_trylock(thread_data[threadID].lock) < 0) {
        return 0;
    }
    if (!UpdateThreadState(threadID, oldState, newState)) {
        pthread_mutex_unlock(thread_data[threadID].lock);
        return 0;
    }
    SetInterrupt(threadID);
    pthread_cond_signal(thread_data[threadID].cond);
    pthread_mutex_unlock(thread_data[threadID].lock);
    return 1;
}

void PauseThread(int threadID)
{
    for (;;) {
        int state = GetThreadState(threadID);
        switch (state & TSTATE_MASK) {
        case TSTATE_RUNNING:
            if (UpdateThreadState(threadID, TSTATE_RUNNING,
                                  TSTATE_PAUSED |
                                      (TLS(threadID) << TSTATE_SHIFT))) {
                SetInterrupt(threadID);
                return;
            }
            break;
        case TSTATE_BLOCKED:
        case TSTATE_SYSCALL:
            if (LockAndUpdateThreadState(threadID, state,
                                         TSTATE_PAUSED |
                                             (TLS(threadID) << TSTATE_SHIFT)))
                return;
            break;
        case TSTATE_PAUSED:
        case TSTATE_TERMINATED:
        case TSTATE_KILLED:
        case TSTATE_INTERRUPTED:
            return;
        }
    }
}

static void TerminateCurrentThread(int locked)
{
    ThreadData * thread = thread_data + TLS(threadID);
    if (locked)
        pthread_mutex_unlock(thread->lock);
    PopRegionLocks(0);
    if (TLS(CurrentHashLock))
        HashUnlock(TLS(CurrentHashLock));
    longjmp(TLS(threadExit), 1);
}

static void PauseCurrentThread(int locked)
{
    ThreadData * thread = thread_data + TLS(threadID);
    if (!locked)
        pthread_mutex_lock(thread->lock);
    for (;;) {
        int state = GetThreadState(TLS(threadID));
        if ((state & TSTATE_MASK) == TSTATE_KILLED)
            TerminateCurrentThread(1);
        if ((state & TSTATE_MASK) != TSTATE_PAUSED)
            break;
        TLS(currentRegion)->alt_owner =
            thread_data[state >> TSTATE_SHIFT].tls;
        pthread_cond_wait(thread->cond, thread->lock);
        // TODO: This really should go in ResumeThread()
        TLS(currentRegion)->alt_owner = NULL;
    }
    if (!locked)
        pthread_mutex_unlock(thread->lock);
}

static void InterruptCurrentThread(int locked, Stat stat)
{
    if (stat == 0)
        return;
    ThreadData * thread = thread_data + TLS(threadID);
    int          state;
    Obj handler = (Obj)0;
    if (!locked)
        pthread_mutex_lock(thread->lock);
    STATE(CurrExecStatFuncs) = ExecStatFuncs;
    SET_BRK_CALL_TO(stat);
    state = GetThreadState(TLS(threadID));
    if ((state & TSTATE_MASK) == TSTATE_INTERRUPTED)
        UpdateThreadState(TLS(threadID), state, TSTATE_RUNNING);
    if (state >> TSTATE_SHIFT) {
        Int n = state >> TSTATE_SHIFT;
        if (TLS(interruptHandlers)) {
            if (n >= 1 && n <= LEN_PLIST(TLS(interruptHandlers)))
                handler = ELM_PLIST(TLS(interruptHandlers), n);
        }
    }
    if (handler)
        CALL_WITH_CATCH(handler, NEW_PLIST(T_PLIST, 0));
    else
        ErrorReturnVoid("system interrupt", 0, 0, "you can 'return;'");
    if (!locked)
        pthread_mutex_unlock(thread->lock);
}

void SetInterruptHandler(int handler, Obj func)
{
    if (!TLS(interruptHandlers)) {
        TLS(interruptHandlers) = NEW_PLIST(T_PLIST, MAX_INTERRUPT);
        SET_LEN_PLIST(TLS(interruptHandlers), MAX_INTERRUPT);
    }
    SET_ELM_PLIST(TLS(interruptHandlers), handler, func);
}

void HandleInterrupts(int locked, Stat stat)
{
    switch (GetThreadState(TLS(threadID)) & TSTATE_MASK) {
    case TSTATE_PAUSED:
        PauseCurrentThread(locked);
        break;
    case TSTATE_INTERRUPTED:
        InterruptCurrentThread(locked, stat);
        break;
    case TSTATE_KILLED:
        TerminateCurrentThread(locked);
        break;
    }
}

void KillThread(int threadID)
{
    for (;;) {
        int state = GetThreadState(threadID);
        switch (state & TSTATE_MASK) {
        case TSTATE_RUNNING:
            if (UpdateThreadState(threadID, TSTATE_RUNNING, TSTATE_KILLED)) {
                SetInterrupt(threadID);
                return;
            }
            break;
        case TSTATE_BLOCKED:
            if (LockAndUpdateThreadState(threadID, state, TSTATE_KILLED))
                return;
            break;
        case TSTATE_SYSCALL:
            if (UpdateThreadState(threadID, state, TSTATE_KILLED)) {
                return;
            }
            break;
        case TSTATE_INTERRUPTED:
            if (UpdateThreadState(threadID, state, TSTATE_KILLED)) {
                SetInterrupt(threadID);
                return;
            }
            break;
        case TSTATE_PAUSED:
            if (LockAndUpdateThreadState(threadID, state, TSTATE_KILLED)) {
                return;
            }
            break;
        case TSTATE_TERMINATED:
        case TSTATE_KILLED:
            return;
        }
    }
}

void InterruptThread(int threadID, int handler)
{
    for (;;) {
        int state = GetThreadState(threadID);
        switch (state & TSTATE_MASK) {
        case TSTATE_RUNNING:
            if (UpdateThreadState(threadID, TSTATE_RUNNING,
                                  TSTATE_INTERRUPTED |
                                      (handler << TSTATE_SHIFT))) {
                SetInterrupt(threadID);
                return;
            }
            break;
        case TSTATE_BLOCKED:
            if (LockAndUpdateThreadState(threadID, state,
                                         TSTATE_INTERRUPTED |
                                             (handler << TSTATE_SHIFT)))
                return;
            break;
        case TSTATE_SYSCALL:
            if (UpdateThreadState(threadID, state,
                                  TSTATE_INTERRUPTED |
                                      (handler << TSTATE_SHIFT)))
                return;
            break;
        case TSTATE_PAUSED:
        case TSTATE_TERMINATED:
        case TSTATE_KILLED:
        case TSTATE_INTERRUPTED:
            // We do not interrupt threads that are interrupted
            return;
        }
    }
}

void ResumeThread(int threadID)
{
    int state = GetThreadState(threadID);
    if ((state & TSTATE_MASK) == TSTATE_PAUSED) {
        LockAndUpdateThreadState(threadID, state, TSTATE_RUNNING);
    }
}

int PauseAllThreads(void)
{
    int i, n;
    LockThreadControl(1);
    if (GlobalPauseInProgress) {
        UnlockThreadControl();
        return 0;
    }
    GlobalPauseInProgress = 1;
    for (i = 0, n = 0; i < MAX_THREADS; i++) {
        switch (GetThreadState(i) & TSTATE_MASK) {
        case TSTATE_TERMINATED:
        case TSTATE_KILLED:
            break;
        default:
            if (!thread_data[i].system)
                paused_threads[n++] = thread_data + i;
            break;
        }
    }
    num_paused_threads = n;
    UnlockThreadControl();
    for (i = 0; i < n; i++)
        PauseThread(i);
    return 1;
}

void ResumeAllThreads(void)
{
    int i, n;
    n = num_paused_threads;
    for (i = 0; i < n; i++) {
        ResumeThread(i);
    }
}

/**
*  Deadlock checks
*  ---------------
*
*  We use a scheme of numerical tiers to implement deadlock checking.
*  Each region is assigned a numerical precedence, and regions must
*  be locked in strictly descending numerical order. If this order
*  is inverted, or if two regions of the same precedence are locked
*  through separate actions, then this is an error.
*
*  Regions with negative precedence are ignored for these tests. This
*  is to facilitate more complex precedence schemes that cannot be
*  embedded in a total ordering.
*/

static Int CurrentRegionPrecedence(void)
{
    Int sp;
    if (!DeadlockCheck || !TLS(lockStack))
        return -1;
    sp = TLS(lockStackPointer);
    while (sp > 0) {
        Obj region_obj = ELM_PLIST(TLS(lockStack), sp);
        if (region_obj) {
            Int prec = ((Region *)(*ADDR_OBJ(region_obj)))->prec;
            if (prec >= 0)
                return prec;
        }
        sp--;
    }
    return -1;
}

int LockObject(Obj obj, LockMode mode)
{
    Region * region = GetRegionOf(obj);
    int      result = TLS(lockStackPointer);
    if (!region)
        return result;

    LockStatus locked = IsLocked(region);
    if (locked == LOCK_STATUS_READONLY_LOCKED && mode == LOCK_MODE_READWRITE)
        return -1;
    if (locked == LOCK_STATUS_UNLOCKED) {
        Int prec = CurrentRegionPrecedence();
        if (prec >= 0 && region->prec >= prec && region->prec >= 0)
            return -1;
        if (region->fixed_owner)
            return -1;
        if (mode == LOCK_MODE_READWRITE)
            RegionWriteLock(region);
        else
            RegionReadLock(region);
        PushRegionLock(region);
    }
    return result;
}

int LockObjects(int count, Obj * objects, const LockMode * mode)
{
    int           result;
    int           i, p;
    Int           curr_prec;
    LockRequest * order;
    if (count == 1) // fast path
        return LockObject(objects[0], mode[0]);
    if (count > MAX_LOCKS)
        return -1;
    order = alloca(sizeof(LockRequest) * count);
    for (i = 0, p = 0; i < count; i++) {
        Region * r = GetRegionOf(objects[i]);
        if (r) {
            order[p].obj = objects[i];
            order[p].region = GetRegionOf(objects[i]);
            order[p].mode = mode[i];
            p++;
        }
    }
    count = p;
    if (p > 1)
        MergeSort(order, count, sizeof(LockRequest), LessThanLockRequest);
    result = TLS(lockStackPointer);
    curr_prec = CurrentRegionPrecedence();
    for (i = 0; i < count; i++) {
        Region * region = order[i].region;
        /* If there are multiple lock requests with different modes,
         * they have been sorted for writes to occur first, so deadlock
         * cannot occur from doing readlocks before writelocks.
         */
        if (i > 0 && region == order[i - 1].region)
            continue; // skip duplicates
        if (!region)
            continue;

        LockStatus locked = IsLocked(region);
        if (locked == LOCK_STATUS_READONLY_LOCKED &&
            order[i].mode == LOCK_MODE_READWRITE) {
            // trying to upgrade read lock to write lock
            PopRegionLocks(result);
            return -1;
        }
        if (!locked) {
            if (curr_prec >= 0 && region->prec >= curr_prec &&
                region->prec >= 0) {
                PopRegionLocks(result);
                return -1;
            }
            if (region->fixed_owner) {
                PopRegionLocks(result);
                return -1;
            }
            if (order[i].mode == LOCK_MODE_READWRITE)
                RegionWriteLock(region);
            else
                RegionReadLock(region);
            PushRegionLock(region);
        }
        if (GetRegionOf(order[i].obj) != region) {
            // Race condition, revert locks and fail
            PopRegionLocks(result);
            return -1;
        }
    }
    return result;
}

int TryLockObjects(int count, Obj * objects, const LockMode * mode)
{
    int           result;
    int           i;
    LockRequest * order;
    if (count > MAX_LOCKS)
        return -1;
    order = alloca(sizeof(LockRequest) * count);
    for (i = 0; i < count; i++) {
        order[i].obj = objects[i];
        order[i].region = GetRegionOf(objects[i]);
        order[i].mode = mode[i];
    }
    MergeSort(order, count, sizeof(LockRequest), LessThanLockRequest);
    result = TLS(lockStackPointer);
    for (i = 0; i < count; i++) {
        Region * region = order[i].region;
        /* If there are multiple lock requests with different modes,
         * they have been sorted for writes to occur first, so deadlock
         * cannot occur from doing readlocks before writelocks.
         */
        if (i > 0 && region == order[i - 1].region)
            continue; // skip duplicates
        if (!region ||
            region->fixed_owner) { // public or thread-local region
            PopRegionLocks(result);
            return -1;
        }
        LockStatus locked = IsLocked(region);
        if (locked == LOCK_STATUS_READONLY_LOCKED &&
            order[i].mode == LOCK_MODE_READWRITE) {
            // trying to upgrade read lock to write lock
            PopRegionLocks(result);
            return -1;
        }
        if (locked == LOCK_STATUS_UNLOCKED) {
            if (order[i].mode == LOCK_MODE_READWRITE) {
                if (!RegionTryWriteLock(region)) {
                    PopRegionLocks(result);
                    return -1;
                }
            }
            else {
                if (!RegionTryReadLock(region)) {
                    PopRegionLocks(result);
                    return -1;
                }
            }
            PushRegionLock(region);
        }
        if (GetRegionOf(order[i].obj) != region) {
            // Race condition, revert locks and fail
            PopRegionLocks(result);
            return -1;
        }
    }
    return result;
}

Region * CurrentRegion(void)
{
    return TLS(currentRegion);
}

#ifdef VERBOSE_GUARDS

static void PrintGuardError(char *       buffer,
                            char *       mode,
                            Obj          obj,
                            const char * file,
                            unsigned     line,
                            const char * func,
                            const char * expr)
{
    sprintf(buffer, "No %s access to object %llu of type %s\n"
                    "in %s, line %u, function %s(), accessing %s",
            mode, (unsigned long long)(UInt)obj, TNAM_OBJ(obj), file, line,
            func, expr);
}
void WriteGuardError(Obj          o,
                     const char * file,
                     unsigned     line,
                     const char * func,
                     const char * expr)
{
    char * buffer = alloca(strlen(file) + strlen(func) + strlen(expr) + 200);
    ImpliedReadGuard(o);
    if (TLS(DisableGuards))
        return;
    SetGVar(&LastInaccessibleGVar, o);
    PrintGuardError(buffer, "write", o, file, line, func, expr);
    ErrorMayQuit("%s", (UInt)buffer, 0);
}

void ReadGuardError(Obj          o,
                    const char * file,
                    unsigned     line,
                    const char * func,
                    const char * expr)
{
    char * buffer = alloca(strlen(file) + strlen(func) + strlen(expr) + 200);
    ImpliedReadGuard(o);
    if (TLS(DisableGuards))
        return;
    SetGVar(&LastInaccessibleGVar, o);
    PrintGuardError(buffer, "read", o, file, line, func, expr);
    ErrorMayQuit("%s", (UInt)buffer, 0);
}

#else
void WriteGuardError(Obj o)
{
    ImpliedReadGuard(o);
    if (TLS(DisableGuards))
        return;
    SetGVar(&LastInaccessibleGVar, o);
    ErrorMayQuit(
        "Attempt to write object %d of type %s without having write access",
        (Int)o, (Int)TNAM_OBJ(o));
}

void ReadGuardError(Obj o)
{
    ImpliedReadGuard(o);
    if (TLS(DisableGuards))
        return;
    SetGVar(&LastInaccessibleGVar, o);
    ErrorMayQuit(
        "Attempt to read object %d of type %s without having read access",
        (Int)o, (Int)TNAM_OBJ(o));
}
#endif

#endif

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