Python/thread_pthread.h

#include "pycore_interp.h"        // _PyInterpreterState.threads.stacksize
#include "pycore_pythread.h"      // _POSIX_SEMAPHORES
#include "pycore_time.h"          // _PyTime_FromMicrosecondsClamup()

/* Posix threads interface */

#include <stdlib.h>
#include <string.h>
#if defined(__APPLE__) || defined(HAVE_PTHREAD_DESTRUCTOR)
#define destructor xxdestructor
#endif
#ifndef HAVE_PTHREAD_STUBS
#  include <pthread.h>
#endif
#if defined(__APPLE__) || defined(HAVE_PTHREAD_DESTRUCTOR)
#undef destructor
#endif
#include <signal.h>
#include <unistd.h>             /* pause(), also getthrid() on OpenBSD */

#ifdef HAVE_GETTID
#   include <unistd.h>          // gettid()
#elif defined(__linux__)
#   include <sys/syscall.h>     /* syscall(SYS_gettid) */
#elif defined(__FreeBSD__)
#   include <pthread_np.h>      /* pthread_getthreadid_np() */
#elif defined(__FreeBSD_kernel__)
#   include <sys/syscall.h>     /* syscall(SYS_thr_self) */
#elif defined(_AIX)
#   include <sys/thread.h>      /* thread_self() */
#elif defined(__NetBSD__)
#   include <lwp.h>             /* _lwp_self() */
#elif defined(__DragonFly__)
#   include <sys/lwp.h>         /* lwp_gettid() */
#elif defined(__sun__) && SIZEOF_LONG >= 8
#   include <thread.h>
#endif

/* The POSIX spec requires that use of pthread_attr_setstacksize
   be conditional on _POSIX_THREAD_ATTR_STACKSIZE being defined. */
#ifdef _POSIX_THREAD_ATTR_STACKSIZE
#ifndef THREAD_STACK_SIZE
#define THREAD_STACK_SIZE       0       /* use default stack size */
#endif

/* The default stack size for new threads on BSD is small enough that
 * we'll get hard crashes instead of 'maximum recursion depth exceeded'
 * exceptions.
 *
 * The default stack size below is the empirically determined minimal stack
 * sizes where a simple recursive function doesn't cause a hard crash.
 *
 * For macOS the value of THREAD_STACK_SIZE is determined in configure.ac
 * as it also depends on the other configure options like chosen sanitizer
 * runtimes.
 */
#if defined(__FreeBSD__) && defined(THREAD_STACK_SIZE) && THREAD_STACK_SIZE == 0
#undef  THREAD_STACK_SIZE
#define THREAD_STACK_SIZE       0x400000
#endif
#if defined(_AIX) && defined(THREAD_STACK_SIZE) && THREAD_STACK_SIZE == 0
#undef  THREAD_STACK_SIZE
#define THREAD_STACK_SIZE       0x200000
#endif
/* bpo-38852: test_threading.test_recursion_limit() checks that 1000 recursive
   Python calls (default recursion limit) doesn't crash, but raise a regular
   RecursionError exception. In debug mode, Python function calls allocates
   more memory on the stack, so use a stack of 8 MiB. */
#if defined(__ANDROID__) && defined(THREAD_STACK_SIZE) && THREAD_STACK_SIZE == 0
#   ifdef Py_DEBUG
#   undef  THREAD_STACK_SIZE
#   define THREAD_STACK_SIZE    0x800000
#   endif
#endif
#if defined(__VXWORKS__) && defined(THREAD_STACK_SIZE) && THREAD_STACK_SIZE == 0
#undef  THREAD_STACK_SIZE
#define THREAD_STACK_SIZE       0x100000
#endif
/* for safety, ensure a viable minimum stacksize */
#define THREAD_STACK_MIN        0x8000  /* 32 KiB */
#else  /* !_POSIX_THREAD_ATTR_STACKSIZE */
#ifdef THREAD_STACK_SIZE
#error "THREAD_STACK_SIZE defined but _POSIX_THREAD_ATTR_STACKSIZE undefined"
#endif
#endif

/* The POSIX spec says that implementations supporting the sem_*
   family of functions must indicate this by defining
   _POSIX_SEMAPHORES. */
#ifdef _POSIX_SEMAPHORES
/* On FreeBSD 4.x, _POSIX_SEMAPHORES is defined empty, so
   we need to add 0 to make it work there as well. */
#if (_POSIX_SEMAPHORES+0) == -1
#  define HAVE_BROKEN_POSIX_SEMAPHORES
#else
#  include <semaphore.h>
#  include <errno.h>
#endif
#endif

/* Thread sanitizer doesn't currently support sem_clockwait */
#ifdef _Py_THREAD_SANITIZER
#undef HAVE_SEM_CLOCKWAIT
#endif


/* On platforms that don't use standard POSIX threads pthread_sigmask()
 * isn't present.  DEC threads uses sigprocmask() instead as do most
 * other UNIX International compliant systems that don't have the full
 * pthread implementation.
 */
#if defined(HAVE_PTHREAD_SIGMASK) && !defined(HAVE_BROKEN_PTHREAD_SIGMASK)
#  define SET_THREAD_SIGMASK pthread_sigmask
#else
#  define SET_THREAD_SIGMASK sigprocmask
#endif


/*
 * pthread_cond support
 */

#define condattr_monotonic _PyRuntime.threads._condattr_monotonic.ptr

static void
init_condattr(void)
{
#ifdef CONDATTR_MONOTONIC
# define ca _PyRuntime.threads._condattr_monotonic.val
    // XXX We need to check the return code?
    pthread_condattr_init(&ca);
    // XXX We need to run pthread_condattr_destroy() during runtime fini.
    if (pthread_condattr_setclock(&ca, CLOCK_MONOTONIC) == 0) {
        condattr_monotonic = &ca;  // Use monotonic clock
    }
# undef ca
#endif  // CONDATTR_MONOTONIC
}

int
_PyThread_cond_init(PyCOND_T *cond)
{
    return pthread_cond_init(cond, condattr_monotonic);
}


void
_PyThread_cond_after(long long us, struct timespec *abs)
{
    PyTime_t timeout = _PyTime_FromMicrosecondsClamp(us);
    PyTime_t t;
#ifdef CONDATTR_MONOTONIC
    if (condattr_monotonic) {
        // silently ignore error: cannot report error to the caller
        (void)PyTime_MonotonicRaw(&t);
    }
    else
#endif
    {
        // silently ignore error: cannot report error to the caller
        (void)PyTime_TimeRaw(&t);
    }
    t = _PyTime_Add(t, timeout);
    _PyTime_AsTimespec_clamp(t, abs);
}


/* A pthread mutex isn't sufficient to model the Python lock type
 * because, according to Draft 5 of the docs (P1003.4a/D5), both of the
 * following are undefined:
 *  -> a thread tries to lock a mutex it already has locked
 *  -> a thread tries to unlock a mutex locked by a different thread
 * pthread mutexes are designed for serializing threads over short pieces
 * of code anyway, so wouldn't be an appropriate implementation of
 * Python's locks regardless.
 *
 * The pthread_lock struct implements a Python lock as a "locked?" bit
 * and a <condition, mutex> pair.  In general, if the bit can be acquired
 * instantly, it is, else the pair is used to block the thread until the
 * bit is cleared.     9 May 1994 tim@ksr.com
 */

typedef struct {
    char             locked; /* 0=unlocked, 1=locked */
    /* a <cond, mutex> pair to handle an acquire of a locked lock */
    pthread_cond_t   lock_released;
    pthread_mutex_t  mut;
} pthread_lock;

#define CHECK_STATUS(name)  if (status != 0) { perror(name); error = 1; }
#define CHECK_STATUS_PTHREAD(name)  if (status != 0) { fprintf(stderr, \
    "%s: %s\n", name, strerror(status)); error = 1; }

/*
 * Initialization for the current runtime.
 */
static void
PyThread__init_thread(void)
{
    // The library is only initialized once in the process,
    // regardless of how many times the Python runtime is initialized.
    static int lib_initialized = 0;
    if (!lib_initialized) {
        lib_initialized = 1;
#if defined(_AIX) && defined(__GNUC__)
        extern void pthread_init(void);
        pthread_init();
#endif
    }
    init_condattr();
}

/*
 * Thread support.
 */

/* bpo-33015: pythread_callback struct and pythread_wrapper() cast
   "void func(void *)" to "void* func(void *)": always return NULL.

   PyThread_start_new_thread() uses "void func(void *)" type, whereas
   pthread_create() requires a void* return value. */
typedef struct {
    void (*func) (void *);
    void *arg;
} pythread_callback;

static void *
pythread_wrapper(void *arg)
{
    /* copy func and func_arg and free the temporary structure */
    pythread_callback *callback = arg;
    void (*func)(void *) = callback->func;
    void *func_arg = callback->arg;
    free(callback);

    func(func_arg);
    return NULL;
}

static int
do_start_joinable_thread(void (*func)(void *), void *arg, pthread_t* out_id)
{
    pthread_t th;
    int status;
#if defined(THREAD_STACK_SIZE) || defined(PTHREAD_SYSTEM_SCHED_SUPPORTED)
    pthread_attr_t attrs;
#endif
#if defined(THREAD_STACK_SIZE)
    size_t      tss;
#endif

    if (!initialized)
        PyThread_init_thread();

#if defined(THREAD_STACK_SIZE) || defined(PTHREAD_SYSTEM_SCHED_SUPPORTED)
    if (pthread_attr_init(&attrs) != 0)
        return -1;
#endif
#if defined(THREAD_STACK_SIZE)
    PyThreadState *tstate = _PyThreadState_GET();
    size_t stacksize = tstate ? tstate->interp->threads.stacksize : 0;
    tss = (stacksize != 0) ? stacksize : THREAD_STACK_SIZE;
    if (tss != 0) {
        if (pthread_attr_setstacksize(&attrs, tss) != 0) {
            pthread_attr_destroy(&attrs);
            return -1;
        }
    }
#endif
#if defined(PTHREAD_SYSTEM_SCHED_SUPPORTED)
    pthread_attr_setscope(&attrs, PTHREAD_SCOPE_SYSTEM);
#endif

    // Use free() instead of PyMem_RawFree() in pythread_wrapper() to avoid a
    // data race if another thread calls PyMem_SetAllocator() in parallel.
    pythread_callback *callback = malloc(sizeof(pythread_callback));

    if (callback == NULL) {
      return -1;
    }

    callback->func = func;
    callback->arg = arg;

    status = pthread_create(&th,
#if defined(THREAD_STACK_SIZE) || defined(PTHREAD_SYSTEM_SCHED_SUPPORTED)
                             &attrs,
#else
                             (pthread_attr_t*)NULL,
#endif
                             pythread_wrapper, callback);

#if defined(THREAD_STACK_SIZE) || defined(PTHREAD_SYSTEM_SCHED_SUPPORTED)
    pthread_attr_destroy(&attrs);
#endif

    if (status != 0) {
        free(callback);
        return -1;
    }
    *out_id = th;
    return 0;
}

/* Helper to convert pthread_t to PyThread_ident_t. POSIX allows pthread_t to be
   non-arithmetic, e.g., musl typedefs it as a pointer. */
static PyThread_ident_t
_pthread_t_to_ident(pthread_t value) {
// Cast through an integer type of the same size to avoid sign-extension.
#if SIZEOF_PTHREAD_T == SIZEOF_VOID_P
    return (uintptr_t) value;
#elif SIZEOF_PTHREAD_T == SIZEOF_LONG
    return (unsigned long) value;
#elif SIZEOF_PTHREAD_T == SIZEOF_INT
    return (unsigned int) value;
#elif SIZEOF_PTHREAD_T == SIZEOF_LONG_LONG
    return (unsigned long long) value;
#else
#error "Unsupported SIZEOF_PTHREAD_T value"
#endif
}

int
PyThread_start_joinable_thread(void (*func)(void *), void *arg,
                               PyThread_ident_t* ident, PyThread_handle_t* handle) {
    pthread_t th = (pthread_t) 0;
    if (do_start_joinable_thread(func, arg, &th)) {
        return -1;
    }
    *ident = _pthread_t_to_ident(th);
    *handle = (PyThread_handle_t) th;
    assert(th == (pthread_t) *handle);
    return 0;
}

unsigned long
PyThread_start_new_thread(void (*func)(void *), void *arg)
{
    pthread_t th = (pthread_t) 0;
    if (do_start_joinable_thread(func, arg, &th)) {
        return PYTHREAD_INVALID_THREAD_ID;
    }
    pthread_detach(th);
    return (unsigned long) _pthread_t_to_ident(th);;
}

int
PyThread_join_thread(PyThread_handle_t th) {
    return pthread_join((pthread_t) th, NULL);
}

int
PyThread_detach_thread(PyThread_handle_t th) {
    return pthread_detach((pthread_t) th);
}

/* XXX This implementation is considered (to quote Tim Peters) "inherently
   hosed" because:
     - It does not guarantee the promise that a non-zero integer is returned.
     - The cast to unsigned long is inherently unsafe.
     - It is not clear that the 'volatile' (for AIX?) are any longer necessary.
*/
PyThread_ident_t
PyThread_get_thread_ident_ex(void) {
    volatile pthread_t threadid;
    if (!initialized)
        PyThread_init_thread();
    threadid = pthread_self();
    return _pthread_t_to_ident(threadid);
}

unsigned long
PyThread_get_thread_ident(void)
{
    return (unsigned long) PyThread_get_thread_ident_ex();
}

#ifdef PY_HAVE_THREAD_NATIVE_ID
unsigned long
PyThread_get_thread_native_id(void)
{
    if (!initialized)
        PyThread_init_thread();
#ifdef __APPLE__
    uint64_t native_id;
    (void) pthread_threadid_np(NULL, &native_id);
#elif defined(HAVE_GETTID)
    pid_t native_id;
    native_id = gettid();
#elif defined(__linux__)
    pid_t native_id;
    native_id = syscall(SYS_gettid);
#elif defined(__FreeBSD__)
    int native_id;
    native_id = pthread_getthreadid_np();
#elif defined(__FreeBSD_kernel__)
    long native_id;
    syscall(SYS_thr_self, &native_id);
#elif defined(__OpenBSD__)
    pid_t native_id;
    native_id = getthrid();
#elif defined(_AIX)
    tid_t native_id;
    native_id = thread_self();
#elif defined(__NetBSD__)
    lwpid_t native_id;
    native_id = _lwp_self();
#elif defined(__DragonFly__)
    // lwp_gettid() is only unique within a process, so combine it with the pid.
    unsigned long native_id = (unsigned long)getpid() << 32 | lwp_gettid();
#elif defined(__sun__) && SIZEOF_LONG >= 8
    unsigned long native_id = (unsigned long)getpid() << 32 | thr_self();
#endif
    return (unsigned long) native_id;
}
#endif

void _Py_NO_RETURN
PyThread_exit_thread(void)
{
    if (!initialized)
        exit(0);
#if defined(__wasi__)
    /*
     * wasi-threads doesn't have pthread_exit right now
     * cf. https://github.com/WebAssembly/wasi-threads/issues/7
     */
    abort();
#else
    pthread_exit(0);
#endif
}

void _Py_NO_RETURN
PyThread_hang_thread(void)
{
    while (1) {
#if defined(__wasi__)
        sleep(9999999);  // WASI doesn't have pause() ?!
#else
        pause();
#endif
    }
}


/* set the thread stack size.
 * Return 0 if size is valid, -1 if size is invalid,
 * -2 if setting stack size is not supported.
 */
static int
_pythread_pthread_set_stacksize(size_t size)
{
#if defined(THREAD_STACK_SIZE)
    pthread_attr_t attrs;
    size_t tss_min;
    int rc = 0;
#endif

    /* set to default */
    if (size == 0) {
        _PyInterpreterState_GET()->threads.stacksize = 0;
        return 0;
    }

#if defined(THREAD_STACK_SIZE)
#if defined(PTHREAD_STACK_MIN)
    tss_min = PTHREAD_STACK_MIN > THREAD_STACK_MIN ? PTHREAD_STACK_MIN
                                                   : THREAD_STACK_MIN;
#else
    tss_min = THREAD_STACK_MIN;
#endif
    if (size >= tss_min) {
        /* validate stack size by setting thread attribute */
        if (pthread_attr_init(&attrs) == 0) {
            rc = pthread_attr_setstacksize(&attrs, size);
            pthread_attr_destroy(&attrs);
            if (rc == 0) {
                _PyInterpreterState_GET()->threads.stacksize = size;
                return 0;
            }
        }
    }
    return -1;
#else
    return -2;
#endif
}

#define THREAD_SET_STACKSIZE(x) _pythread_pthread_set_stacksize(x)


/* Thread Local Storage (TLS) API

   This API is DEPRECATED since Python 3.7.  See PEP 539 for details.
*/

/* Issue #25658: On platforms where native TLS key is defined in a way that
   cannot be safely cast to int, PyThread_create_key returns immediately a
   failure status and other TLS functions all are no-ops.  This indicates
   clearly that the old API is not supported on platforms where it cannot be
   used reliably, and that no effort will be made to add such support.

   Note: PTHREAD_KEY_T_IS_COMPATIBLE_WITH_INT will be unnecessary after
   removing this API.
*/

int
PyThread_create_key(void)
{
#ifdef PTHREAD_KEY_T_IS_COMPATIBLE_WITH_INT
    pthread_key_t key;
    int fail = pthread_key_create(&key, NULL);
    if (fail)
        return -1;
    if (key > INT_MAX) {
        /* Issue #22206: handle integer overflow */
        pthread_key_delete(key);
        errno = ENOMEM;
        return -1;
    }
    return (int)key;
#else
    return -1;  /* never return valid key value. */
#endif
}

void
PyThread_delete_key(int key)
{
#ifdef PTHREAD_KEY_T_IS_COMPATIBLE_WITH_INT
    pthread_key_delete(key);
#endif
}

void
PyThread_delete_key_value(int key)
{
#ifdef PTHREAD_KEY_T_IS_COMPATIBLE_WITH_INT
    pthread_setspecific(key, NULL);
#endif
}

int
PyThread_set_key_value(int key, void *value)
{
#ifdef PTHREAD_KEY_T_IS_COMPATIBLE_WITH_INT
    int fail = pthread_setspecific(key, value);
    return fail ? -1 : 0;
#else
    return -1;
#endif
}

void *
PyThread_get_key_value(int key)
{
#ifdef PTHREAD_KEY_T_IS_COMPATIBLE_WITH_INT
    return pthread_getspecific(key);
#else
    return NULL;
#endif
}


void
PyThread_ReInitTLS(void)
{
}


/* Thread Specific Storage (TSS) API

   Platform-specific components of TSS API implementation.
*/

int
PyThread_tss_create(Py_tss_t *key)
{
    assert(key != NULL);
    /* If the key has been created, function is silently skipped. */
    if (key->_is_initialized) {
        return 0;
    }

    int fail = pthread_key_create(&(key->_key), NULL);
    if (fail) {
        return -1;
    }
    key->_is_initialized = 1;
    return 0;
}

void
PyThread_tss_delete(Py_tss_t *key)
{
    assert(key != NULL);
    /* If the key has not been created, function is silently skipped. */
    if (!key->_is_initialized) {
        return;
    }

    pthread_key_delete(key->_key);
    /* pthread has not provided the defined invalid value for the key. */
    key->_is_initialized = 0;
}

int
PyThread_tss_set(Py_tss_t *key, void *value)
{
    assert(key != NULL);
    int fail = pthread_setspecific(key->_key, value);
    return fail ? -1 : 0;
}

void *
PyThread_tss_get(Py_tss_t *key)
{
    assert(key != NULL);
    return pthread_getspecific(key->_key);
}