cosmopolitan/third_party/python/Python/thread.c

/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=4 sts=4 sw=4 fenc=utf-8                                :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Python 3                                                                     │
│ https://docs.python.org/3/license.html                                       │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/assert.h"
#include "third_party/python/Include/pyerrors.h"
#include "third_party/python/Include/pymacro.h"
#include "third_party/python/Include/pymem.h"
#include "third_party/python/Include/pythread.h"
#include "third_party/python/Include/structseq.h"
/* clang-format off */

/* Thread package.
   This is intended to be usable independently from Python.
   The implementation for system foobar is in a file thread_foobar.inc
   which is included by this file dependent on config settings.
   Stuff shared by all thread_*.h files is collected here. */

#ifndef _POSIX_THREADS

/* Check if we're running on HP-UX and _SC_THREADS is defined. If so, then
   enough of the Posix threads package is implemented to support python
   threads.

   This is valid for HP-UX 11.23 running on an ia64 system. If needed, add
   a check of __ia64 to verify that we're running on an ia64 system instead
   of a pa-risc system.
*/
#ifdef __hpux
#ifdef _SC_THREADS
#define _POSIX_THREADS
#endif
#endif

#endif /* _POSIX_THREADS */


#ifdef Py_DEBUG
static int thread_debug = 0;
#define dprintf(args)   (void)((thread_debug & 1) && printf args)
#define d2printf(args)  ((thread_debug & 8) && printf args)
#else
#define dprintf(args)
#define d2printf(args)
#endif

static int initialized;

static void PyThread__init_thread(void); /* Forward */

void
PyThread_init_thread(void)
{
#ifdef Py_DEBUG
    char *p = Py_GETENV("PYTHONTHREADDEBUG");

    if (p) {
        if (*p)
            thread_debug = atoi(p);
        else
            thread_debug = 1;
    }
#endif /* Py_DEBUG */
    if (initialized)
        return;
    initialized = 1;
    dprintf(("PyThread_init_thread called\n"));
    PyThread__init_thread();
}

/* Support for runtime thread stack size tuning.
   A value of 0 means using the platform's default stack size
   or the size specified by the THREAD_STACK_SIZE macro. */
static size_t _pythread_stacksize = 0;

#ifdef _POSIX_THREADS
#define PYTHREAD_NAME "pthread"
#include "thread_pthread.inc"
#endif

#ifdef NT_THREADS
#define PYTHREAD_NAME "nt"
#include "thread_nt.inc"
#endif


/*
#ifdef FOOBAR_THREADS
#include "thread_foobar.inc"
#endif
*/

/* return the current thread stack size */
size_t
PyThread_get_stacksize(void)
{
    return _pythread_stacksize;
}

/* Only platforms defining a THREAD_SET_STACKSIZE() macro
   in thread_<platform>.h support changing the stack size.
   Return 0 if stack size is valid,
      -1 if stack size value is invalid,
      -2 if setting stack size is not supported. */
int
PyThread_set_stacksize(size_t size)
{
#if defined(THREAD_SET_STACKSIZE)
    return THREAD_SET_STACKSIZE(size);
#else
    return -2;
#endif
}

#ifndef Py_HAVE_NATIVE_TLS
/* If the platform has not supplied a platform specific
   TLS implementation, provide our own.

   This code stolen from "thread_sgi.h", where it was the only
   implementation of an existing Python TLS API.
*/
/* ------------------------------------------------------------------------
Per-thread data ("key") support.

Use PyThread_create_key() to create a new key.  This is typically shared
across threads.

Use PyThread_set_key_value(thekey, value) to associate void* value with
thekey in the current thread.  Each thread has a distinct mapping of thekey
to a void* value.  Caution:  if the current thread already has a mapping
for thekey, value is ignored.

Use PyThread_get_key_value(thekey) to retrieve the void* value associated
with thekey in the current thread.  This returns NULL if no value is
associated with thekey in the current thread.

Use PyThread_delete_key_value(thekey) to forget the current thread's associated
value for thekey.  PyThread_delete_key(thekey) forgets the values associated
with thekey across *all* threads.

While some of these functions have error-return values, none set any
Python exception.

None of the functions does memory management on behalf of the void* values.
You need to allocate and deallocate them yourself.  If the void* values
happen to be PyObject*, these functions don't do refcount operations on
them either.

The GIL does not need to be held when calling these functions; they supply
their own locking.  This isn't true of PyThread_create_key(), though (see
next paragraph).

There's a hidden assumption that PyThread_create_key() will be called before
any of the other functions are called.  There's also a hidden assumption
that calls to PyThread_create_key() are serialized externally.
------------------------------------------------------------------------ */

/* A singly-linked list of struct key objects remembers all the key->value
 * associations.  File static keyhead heads the list.  keymutex is used
 * to enforce exclusion internally.
 */
struct key {
    /* Next record in the list, or NULL if this is the last record. */
    struct key *next;

    /* The thread id, according to PyThread_get_thread_ident(). */
    long id;

    /* The key and its associated value. */
    int key;
    void *value;
};

static struct key *keyhead = NULL;
static PyThread_type_lock keymutex = NULL;
static int nkeys = 0;  /* PyThread_create_key() hands out nkeys+1 next */

/* Internal helper.
 * If the current thread has a mapping for key, the appropriate struct key*
 * is returned.  NB:  value is ignored in this case!
 * If there is no mapping for key in the current thread, then:
 *     If value is NULL, NULL is returned.
 *     Else a mapping of key to value is created for the current thread,
 *     and a pointer to a new struct key* is returned; except that if
 *     malloc() can't find room for a new struct key*, NULL is returned.
 * So when value==NULL, this acts like a pure lookup routine, and when
 * value!=NULL, this acts like dict.setdefault(), returning an existing
 * mapping if one exists, else creating a new mapping.
 *
 * Caution:  this used to be too clever, trying to hold keymutex only
 * around the "p->next = keyhead; keyhead = p" pair.  That allowed
 * another thread to mutate the list, via key deletion, concurrent with
 * find_key() crawling over the list.  Hilarity ensued.  For example, when
 * the for-loop here does "p = p->next", p could end up pointing at a
 * record that PyThread_delete_key_value() was concurrently free()'ing.
 * That could lead to anything, from failing to find a key that exists, to
 * segfaults.  Now we lock the whole routine.
 */
static struct key *
find_key(int set_value, int key, void *value)
{
    struct key *p, *prev_p;
    long id = PyThread_get_thread_ident();

    if (!keymutex)
        return NULL;
    PyThread_acquire_lock(keymutex, 1);
    prev_p = NULL;
    for (p = keyhead; p != NULL; p = p->next) {
        if (p->id == id && p->key == key) {
            if (set_value)
                p->value = value;
            goto Done;
        }
        /* Sanity check.  These states should never happen but if
         * they do we must abort.  Otherwise we'll end up spinning
         * in a tight loop with the lock held.  A similar check is done
         * in pystate.c tstate_delete_common().  */
        if (p == prev_p)
            Py_FatalError("tls find_key: small circular list(!)");
        prev_p = p;
        if (p->next == keyhead)
            Py_FatalError("tls find_key: circular list(!)");
    }
    if (!set_value && value == NULL) {
        assert(p == NULL);
        goto Done;
    }
    p = (struct key *)PyMem_RawMalloc(sizeof(struct key));
    if (p != NULL) {
        p->id = id;
        p->key = key;
        p->value = value;
        p->next = keyhead;
        keyhead = p;
    }
 Done:
    PyThread_release_lock(keymutex);
    return p;
}

/* Return a new key.  This must be called before any other functions in
 * this family, and callers must arrange to serialize calls to this
 * function.  No violations are detected.
 */
int
PyThread_create_key(void)
{
    /* All parts of this function are wrong if it's called by multiple
     * threads simultaneously.
     */
    if (keymutex == NULL)
        keymutex = PyThread_allocate_lock();
    return ++nkeys;
}

/* Forget the associations for key across *all* threads. */
void
PyThread_delete_key(int key)
{
    struct key *p, **q;

    PyThread_acquire_lock(keymutex, 1);
    q = &keyhead;
    while ((p = *q) != NULL) {
        if (p->key == key) {
            *q = p->next;
            PyMem_RawFree((void *)p);
            /* NB This does *not* free p->value! */
        }
        else
            q = &p->next;
    }
    PyThread_release_lock(keymutex);
}

int
PyThread_set_key_value(int key, void *value)
{
    struct key *p;

    p = find_key(1, key, value);
    if (p == NULL)
        return -1;
    else
        return 0;
}

/* Retrieve the value associated with key in the current thread, or NULL
 * if the current thread doesn't have an association for key.
 */
void *
PyThread_get_key_value(int key)
{
    struct key *p = find_key(0, key, NULL);

    if (p == NULL)
        return NULL;
    else
        return p->value;
}

/* Forget the current thread's association for key, if any. */
void
PyThread_delete_key_value(int key)
{
    long id = PyThread_get_thread_ident();
    struct key *p, **q;

    PyThread_acquire_lock(keymutex, 1);
    q = &keyhead;
    while ((p = *q) != NULL) {
        if (p->key == key && p->id == id) {
            *q = p->next;
            PyMem_RawFree((void *)p);
            /* NB This does *not* free p->value! */
            break;
        }
        else
            q = &p->next;
    }
    PyThread_release_lock(keymutex);
}

/* Forget everything not associated with the current thread id.
 * This function is called from PyOS_AfterFork().  It is necessary
 * because other thread ids which were in use at the time of the fork
 * may be reused for new threads created in the forked process.
 */
void
PyThread_ReInitTLS(void)
{
    long id = PyThread_get_thread_ident();
    struct key *p, **q;

    if (!keymutex)
        return;

    /* As with interpreter_lock in PyEval_ReInitThreads()
       we just create a new lock without freeing the old one */
    keymutex = PyThread_allocate_lock();

    /* Delete all keys which do not match the current thread id */
    q = &keyhead;
    while ((p = *q) != NULL) {
        if (p->id != id) {
            *q = p->next;
            PyMem_RawFree((void *)p);
            /* NB This does *not* free p->value! */
        }
        else
            q = &p->next;
    }
}

#endif /* Py_HAVE_NATIVE_TLS */

PyDoc_STRVAR(threadinfo__doc__,
"sys.thread_info\n\
\n\
A struct sequence holding information about the thread implementation.");

static PyStructSequence_Field threadinfo_fields[] = {
    {"name",    PyDoc_STR("name of the thread implementation")},
    {"lock",    PyDoc_STR("name of the lock implementation")},
    {"version", PyDoc_STR("name and version of the thread library")},
    {0}
};

static PyStructSequence_Desc threadinfo_desc = {
    "sys.thread_info",           /* name */
    threadinfo__doc__,           /* doc */
    threadinfo_fields,           /* fields */
    3
};

static PyTypeObject ThreadInfoType;

PyObject*
PyThread_GetInfo(void)
{
    PyObject *threadinfo, *value;
    int pos = 0;
#if (defined(_POSIX_THREADS) && defined(HAVE_CONFSTR) \
     && defined(_CS_GNU_LIBPTHREAD_VERSION))
    char buffer[255];
    int len;
#endif

    if (ThreadInfoType.tp_name == 0) {
        if (PyStructSequence_InitType2(&ThreadInfoType, &threadinfo_desc) < 0)
            return NULL;
    }

    threadinfo = PyStructSequence_New(&ThreadInfoType);
    if (threadinfo == NULL)
        return NULL;

    value = PyUnicode_FromString(PYTHREAD_NAME);
    if (value == NULL) {
        Py_DECREF(threadinfo);
        return NULL;
    }
    PyStructSequence_SET_ITEM(threadinfo, pos++, value);

#ifdef _POSIX_THREADS
#ifdef USE_SEMAPHORES
    value = PyUnicode_FromString("semaphore");
#else
    value = PyUnicode_FromString("mutex+cond");
#endif
    if (value == NULL) {
        Py_DECREF(threadinfo);
        return NULL;
    }
#else
    Py_INCREF(Py_None);
    value = Py_None;
#endif
    PyStructSequence_SET_ITEM(threadinfo, pos++, value);

#if (defined(_POSIX_THREADS) && defined(HAVE_CONFSTR) \
     && defined(_CS_GNU_LIBPTHREAD_VERSION))
    value = NULL;
    len = confstr(_CS_GNU_LIBPTHREAD_VERSION, buffer, sizeof(buffer));
    if (1 < len && (size_t)len < sizeof(buffer)) {
        value = PyUnicode_DecodeFSDefaultAndSize(buffer, len-1);
        if (value == NULL)
            PyErr_Clear();
    }
    if (value == NULL)
#endif
    {
        Py_INCREF(Py_None);
        value = Py_None;
    }
    PyStructSequence_SET_ITEM(threadinfo, pos++, value);
    return threadinfo;
}