387 lines
11 KiB
C
387 lines
11 KiB
C
/* Copyright (C) 2002, 2003, 2004, 2005 Free Software Foundation, Inc.
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Contributed by Zack Weinberg <zack@codesourcery.com>
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This file is part of GCC.
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GCC is free software; you can redistribute it and/or modify it under
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the terms of the GNU General Public License as published by the Free
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Software Foundation; either version 2, or (at your option) any later
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version.
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GCC is distributed in the hope that it will be useful, but WITHOUT ANY
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WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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for more details.
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You should have received a copy of the GNU General Public License
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along with GCC; see the file COPYING. If not, write to the Free
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Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
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02110-1301, USA. */
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/* As a special exception, if you link this library with other files,
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some of which are compiled with GCC, to produce an executable,
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this library does not by itself cause the resulting executable
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to be covered by the GNU General Public License.
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This exception does not however invalidate any other reasons why
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the executable file might be covered by the GNU General Public License. */
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/* Threads compatibility routines for libgcc2 for VxWorks.
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These are out-of-line routines called from gthr-vxworks.h. */
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#include "tconfig.h"
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#include "tsystem.h"
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#include "gthr.h"
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#if defined(__GTHREADS)
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#include <vxWorks.h>
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#ifndef __RTP__
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#include <vxLib.h>
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#endif
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#include <taskLib.h>
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#ifndef __RTP__
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#include <taskHookLib.h>
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#else
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# include <errno.h>
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#endif
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/* Init-once operation.
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This would be a clone of the implementation from gthr-solaris.h,
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except that we have a bootstrap problem - the whole point of this
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exercise is to prevent double initialization, but if two threads
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are racing with each other, once->mutex is liable to be initialized
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by both. Then each thread will lock its own mutex, and proceed to
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call the initialization routine.
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So instead we use a bare atomic primitive (vxTas()) to handle
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mutual exclusion. Threads losing the race then busy-wait, calling
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taskDelay() to yield the processor, until the initialization is
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completed. Inefficient, but reliable. */
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int
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__gthread_once (__gthread_once_t *guard, void (*func)(void))
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{
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if (guard->done)
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return 0;
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#ifdef __RTP__
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__gthread_lock_library ();
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#else
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while (!vxTas ((void *)&guard->busy))
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taskDelay (1);
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#endif
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/* Only one thread at a time gets here. Check ->done again, then
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go ahead and call func() if no one has done it yet. */
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if (!guard->done)
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{
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func ();
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guard->done = 1;
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}
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#ifdef __RTP__
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__gthread_unlock_library ();
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#else
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guard->busy = 0;
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#endif
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return 0;
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}
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/* Thread-local storage.
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We reserve a field in the TCB to point to a dynamically allocated
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array which is used to store TLS values. A TLS key is simply an
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offset in this array. The exact location of the TCB field is not
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known to this code nor to vxlib.c -- all access to it indirects
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through the routines __gthread_get_tls_data and
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__gthread_set_tls_data, which are provided by the VxWorks kernel.
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There is also a global array which records which keys are valid and
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which have destructors.
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A task delete hook is installed to execute key destructors. The
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routines __gthread_enter_tls_dtor_context and
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__gthread_leave_tls_dtor_context, which are also provided by the
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kernel, ensure that it is safe to call free() on memory allocated
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by the task being deleted. (This is a no-op on VxWorks 5, but
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a major undertaking on AE.)
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The task delete hook is only installed when at least one thread
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has TLS data. This is a necessary precaution, to allow this module
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to be unloaded - a module with a hook can not be removed.
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Since this interface is used to allocate only a small number of
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keys, the table size is small and static, which simplifies the
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code quite a bit. Revisit this if and when it becomes necessary. */
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#define MAX_KEYS 4
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/* This is the structure pointed to by the pointer returned
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by __gthread_get_tls_data. */
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struct tls_data
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{
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int *owner;
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void *values[MAX_KEYS];
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unsigned int generation[MAX_KEYS];
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};
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/* To make sure we only delete TLS data associated with this object,
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include a pointer to a local variable in the TLS data object. */
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static int self_owner;
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/* The number of threads for this module which have active TLS data.
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This is protected by tls_lock. */
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static int active_tls_threads;
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/* kernel provided routines */
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extern void *__gthread_get_tls_data (void);
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extern void __gthread_set_tls_data (void *data);
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extern void __gthread_enter_tls_dtor_context (void);
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extern void __gthread_leave_tls_dtor_context (void);
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/* This is a global structure which records all of the active keys.
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A key is potentially valid (i.e. has been handed out by
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__gthread_key_create) iff its generation count in this structure is
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even. In that case, the matching entry in the dtors array is a
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routine to be called when a thread terminates with a valid,
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non-NULL specific value for that key.
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A key is actually valid in a thread T iff the generation count
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stored in this structure is equal to the generation count stored in
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T's specific-value structure. */
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typedef void (*tls_dtor) (void *);
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struct tls_keys
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{
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tls_dtor dtor[MAX_KEYS];
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unsigned int generation[MAX_KEYS];
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};
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#define KEY_VALID_P(key) !(tls_keys.generation[key] & 1)
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/* Note: if MAX_KEYS is increased, this initializer must be updated
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to match. All the generation counts begin at 1, which means no
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key is valid. */
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static struct tls_keys tls_keys =
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{
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{ 0, 0, 0, 0 },
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{ 1, 1, 1, 1 }
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};
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/* This lock protects the tls_keys structure. */
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static __gthread_mutex_t tls_lock;
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static __gthread_once_t tls_init_guard = __GTHREAD_ONCE_INIT;
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/* Internal routines. */
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/* The task TCB has just been deleted. Call the destructor
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function for each TLS key that has both a destructor and
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a non-NULL specific value in this thread.
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This routine does not need to take tls_lock; the generation
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count protects us from calling a stale destructor. It does
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need to read tls_keys.dtor[key] atomically. */
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static void
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tls_delete_hook (void *tcb ATTRIBUTE_UNUSED)
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{
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struct tls_data *data = __gthread_get_tls_data ();
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__gthread_key_t key;
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if (data && data->owner == &self_owner)
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{
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__gthread_enter_tls_dtor_context ();
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for (key = 0; key < MAX_KEYS; key++)
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{
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if (data->generation[key] == tls_keys.generation[key])
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{
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tls_dtor dtor = tls_keys.dtor[key];
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if (dtor)
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dtor (data->values[key]);
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}
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}
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free (data);
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/* We can't handle an error here, so just leave the thread
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marked as loaded if one occurs. */
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if (__gthread_mutex_lock (&tls_lock) != ERROR)
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{
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active_tls_threads--;
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if (active_tls_threads == 0)
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taskDeleteHookDelete ((FUNCPTR)tls_delete_hook);
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__gthread_mutex_unlock (&tls_lock);
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}
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__gthread_set_tls_data (0);
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__gthread_leave_tls_dtor_context ();
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}
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}
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/* Initialize global data used by the TLS system. */
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static void
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tls_init (void)
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{
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__GTHREAD_MUTEX_INIT_FUNCTION (&tls_lock);
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}
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static void tls_destructor (void) __attribute__ ((destructor));
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static void
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tls_destructor (void)
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{
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#ifdef __RTP__
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/* All threads but this one should have exited by now. */
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tls_delete_hook (NULL);
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#else
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/* Unregister the hook forcibly. The counter of active threads may
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be incorrect, because constructors (like the C++ library's) and
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destructors (like this one) run in the context of the shell rather
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than in a task spawned from this module. */
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taskDeleteHookDelete ((FUNCPTR)tls_delete_hook);
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#endif
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if (tls_init_guard.done && __gthread_mutex_lock (&tls_lock) != ERROR)
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semDelete (tls_lock);
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}
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/* External interface */
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/* Store in KEYP a value which can be passed to __gthread_setspecific/
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__gthread_getspecific to store and retrieve a value which is
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specific to each calling thread. If DTOR is not NULL, it will be
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called when a thread terminates with a non-NULL specific value for
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this key, with the value as its sole argument. */
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int
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__gthread_key_create (__gthread_key_t *keyp, tls_dtor dtor)
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{
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__gthread_key_t key;
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__gthread_once (&tls_init_guard, tls_init);
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if (__gthread_mutex_lock (&tls_lock) == ERROR)
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return errno;
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for (key = 0; key < MAX_KEYS; key++)
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if (!KEY_VALID_P (key))
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goto found_slot;
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/* no room */
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__gthread_mutex_unlock (&tls_lock);
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return EAGAIN;
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found_slot:
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tls_keys.generation[key]++; /* making it even */
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tls_keys.dtor[key] = dtor;
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*keyp = key;
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__gthread_mutex_unlock (&tls_lock);
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return 0;
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}
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/* Invalidate KEY; it can no longer be used as an argument to
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setspecific/getspecific. Note that this does NOT call destructor
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functions for any live values for this key. */
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int
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__gthread_key_delete (__gthread_key_t key)
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{
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if (key >= MAX_KEYS)
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return EINVAL;
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__gthread_once (&tls_init_guard, tls_init);
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if (__gthread_mutex_lock (&tls_lock) == ERROR)
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return errno;
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if (!KEY_VALID_P (key))
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{
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__gthread_mutex_unlock (&tls_lock);
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return EINVAL;
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}
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tls_keys.generation[key]++; /* making it odd */
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tls_keys.dtor[key] = 0;
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__gthread_mutex_unlock (&tls_lock);
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return 0;
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}
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/* Retrieve the thread-specific value for KEY. If it has never been
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set in this thread, or KEY is invalid, returns NULL.
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It does not matter if this function races with key_create or
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key_delete; the worst that can happen is you get a value other than
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the one that a serialized implementation would have provided. */
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void *
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__gthread_getspecific (__gthread_key_t key)
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{
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struct tls_data *data;
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if (key >= MAX_KEYS)
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return 0;
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data = __gthread_get_tls_data ();
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if (!data)
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return 0;
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if (data->generation[key] != tls_keys.generation[key])
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return 0;
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return data->values[key];
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}
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/* Set the thread-specific value for KEY. If KEY is invalid, or
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memory allocation fails, returns -1, otherwise 0.
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The generation count protects this function against races with
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key_create/key_delete; the worst thing that can happen is that a
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value is successfully stored into a dead generation (and then
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immediately becomes invalid). However, we do have to make sure
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to read tls_keys.generation[key] atomically. */
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int
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__gthread_setspecific (__gthread_key_t key, void *value)
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{
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struct tls_data *data;
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unsigned int generation;
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if (key >= MAX_KEYS)
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return EINVAL;
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data = __gthread_get_tls_data ();
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if (!data)
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{
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if (__gthread_mutex_lock (&tls_lock) == ERROR)
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return ENOMEM;
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if (active_tls_threads == 0)
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taskDeleteHookAdd ((FUNCPTR)tls_delete_hook);
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active_tls_threads++;
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__gthread_mutex_unlock (&tls_lock);
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data = malloc (sizeof (struct tls_data));
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if (!data)
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return ENOMEM;
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memset (data, 0, sizeof (struct tls_data));
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data->owner = &self_owner;
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__gthread_set_tls_data (data);
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}
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generation = tls_keys.generation[key];
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if (generation & 1)
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return EINVAL;
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data->generation[key] = generation;
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data->values[key] = value;
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return 0;
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}
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#endif /* __GTHREADS */
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