SDL_spinlock.c

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Author : Sam Lantinga
Date : 2014-07-07 21:27:42
Hash : 8077bf3d
Message : Fixed bug 2618 - incomplete pthread-based lock support should be removed binarycrusader Since changeset 358696c354a8, SDL 2.0 has been broken on Solaris when compiling with the Solaris Studio compiler (which uses the pthread implementation of SDL_AtomicLock). Notably, it gets stuck at the MemoryBarrierRelease in SDL_GetErrBuf: 6585 # 218 6586 if (!tls_errbuf && !tls_being_created) { 6587 SDL_AtomicLock_REAL ( & tls_lock ); 6588 if (!tls_errbuf) { 6589 SDL_TLSID slot; 6590 tls_being_created = SDL_TRUE; 6591 slot = SDL_TLSCreate_REAL ( ); 6592 tls_being_created = SDL_FALSE; 6593 { SDL_SpinLock _tmp = 0 ; SDL_AtomicLock_REAL ( & _tmp ) ; SDL_AtomicUnlock_REAL ( & _tmp ) ; }; ^^^ loops forever above 6594 tls_errbuf = slot; 6595 } 6596 SDL_AtomicUnlock_REAL ( & tls_lock ); 6597 } Running: testthread (process id 28926) ^Cdbx: warning: Interrupt ignored but forwarded to child. signal INT (Interrupt) in __nanosleep at 0xfe52a875 0xfe52a875: __nanosleep+0x0015: jae __nanosleep+0x23 [ 0xfe52a883, .+0xe ] Current function is SDL_Delay_REAL 204 was_error = nanosleep(&tv, &elapsed); (dbx) where [1] __nanosleep(0xfeffe848, 0xfeffe850, 0xfe75a5ac, 0xfe5169d8), at 0xfe52a875 [2] nanosleep(0xfeffe848, 0xfeffe850), at 0xfe516a3b =>[3] SDL_Delay_REAL(ms = 0), line 204 in "SDL_systimer.c" [4] SDL_AtomicLock_REAL(lock = 0xfeffe88c), line 104 in "SDL_spinlock.c" [5] SDL_GetErrBuf(), line 225 in "SDL_thread.c" [6] SDL_ClearError_REAL(), line 216 in "SDL_error.c" [7] SDL_InitSubSystem_REAL(flags = 0), line 116 in "SDL.c" [8] SDL_Init_REAL(flags = 0), line 244 in "SDL.c" [9] SDL_Init(a = 0), line 89 in "SDL_dynapi_procs.h" [10] main(argc = 1, argv = 0xfeffe948), line 65 in "testthread.c" As far as I can tell, this is because pthread_spin_trylock() always returns EBUSY for this particular lock; since it works in other places, I'm suspicious. Different Solaris Studio compiler versions seem to make no difference. I've verified this is broken on Linux as well if SDL_spinlock.c is modified to use the pthread implementation. This appears to be because pthread_spin_init() and pthread_spin_destroy() are not used with the locks as required.

src/atomic/SDL_spinlock.c

/*
  Simple DirectMedia Layer
  Copyright (C) 1997-2014 Sam Lantinga <slouken@libsdl.org>

  This software is provided 'as-is', without any express or implied
  warranty.  In no event will the authors be held liable for any damages
  arising from the use of this software.

  Permission is granted to anyone to use this software for any purpose,
  including commercial applications, and to alter it and redistribute it
  freely, subject to the following restrictions:

  1. The origin of this software must not be misrepresented; you must not
     claim that you wrote the original software. If you use this software
     in a product, an acknowledgment in the product documentation would be
     appreciated but is not required.
  2. Altered source versions must be plainly marked as such, and must not be
     misrepresented as being the original software.
  3. This notice may not be removed or altered from any source distribution.
*/
#include "../SDL_internal.h"

#if defined(__WIN32__) || defined(__WINRT__)
#include "../core/windows/SDL_windows.h"
#endif

#include "SDL_atomic.h"
#include "SDL_mutex.h"
#include "SDL_timer.h"

#if !defined(HAVE_GCC_ATOMICS) && defined(__SOLARIS__)
#include <atomic.h>
#endif

/* This function is where all the magic happens... */
SDL_bool
SDL_AtomicTryLock(SDL_SpinLock *lock)
{
#if SDL_ATOMIC_DISABLED
    /* Terrible terrible damage */
    static SDL_mutex *_spinlock_mutex;

    if (!_spinlock_mutex) {
        /* Race condition on first lock... */
        _spinlock_mutex = SDL_CreateMutex();
    }
    SDL_LockMutex(_spinlock_mutex);
    if (*lock == 0) {
        *lock = 1;
        SDL_UnlockMutex(_spinlock_mutex);
        return SDL_TRUE;
    } else {
        SDL_UnlockMutex(_spinlock_mutex);
        return SDL_FALSE;
    }

#elif defined(_MSC_VER)
    SDL_COMPILE_TIME_ASSERT(locksize, sizeof(*lock) == sizeof(long));
    return (InterlockedExchange((long*)lock, 1) == 0);

#elif HAVE_GCC_ATOMICS || HAVE_GCC_SYNC_LOCK_TEST_AND_SET
    return (__sync_lock_test_and_set(lock, 1) == 0);

#elif defined(__GNUC__) && defined(__arm__) && \
        (defined(__ARM_ARCH_4__) || defined(__ARM_ARCH_4T__) || \
         defined(__ARM_ARCH_5__) || defined(__ARM_ARCH_5TE__) || \
         defined(__ARM_ARCH_5TEJ__))
    int result;
    __asm__ __volatile__ (
        "swp %0, %1, [%2]\n"
        : "=&r,&r" (result) : "r,0" (1), "r,r" (lock) : "memory");
    return (result == 0);

#elif defined(__GNUC__) && defined(__arm__)
    int result;
    __asm__ __volatile__ (
        "ldrex %0, [%2]\nteq   %0, #0\nstrexeq %0, %1, [%2]"
        : "=&r" (result) : "r" (1), "r" (lock) : "cc", "memory");
    return (result == 0);

#elif defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
    int result;
    __asm__ __volatile__(
        "lock ; xchgl %0, (%1)\n"
        : "=r" (result) : "r" (lock), "0" (1) : "cc", "memory");
    return (result == 0);

#elif defined(__MACOSX__) || defined(__IPHONEOS__)
    /* Maybe used for PowerPC, but the Intel asm or gcc atomics are favored. */
    return OSAtomicCompareAndSwap32Barrier(0, 1, lock);

#elif defined(__SOLARIS__) && defined(_LP64)
    /* Used for Solaris with non-gcc compilers. */
    return (SDL_bool) ((int) atomic_cas_64((volatile uint64_t*)lock, 0, 1) == 0);

#elif defined(__SOLARIS__) && !defined(_LP64)
    /* Used for Solaris with non-gcc compilers. */
    return (SDL_bool) ((int) atomic_cas_32((volatile uint32_t*)lock, 0, 1) == 0);

#else
#error Please implement for your platform.
    return SDL_FALSE;
#endif
}

void
SDL_AtomicLock(SDL_SpinLock *lock)
{
    /* FIXME: Should we have an eventual timeout? */
    while (!SDL_AtomicTryLock(lock)) {
        SDL_Delay(0);
    }
}

void
SDL_AtomicUnlock(SDL_SpinLock *lock)
{
#if defined(_MSC_VER)
    _ReadWriteBarrier();
    *lock = 0;

#elif HAVE_GCC_ATOMICS || HAVE_GCC_SYNC_LOCK_TEST_AND_SET
    __sync_lock_release(lock);

#elif defined(__SOLARIS__)
    /* Used for Solaris when not using gcc. */
    *lock = 0;
    membar_producer();

#else
    *lock = 0;
#endif
}

/* vi: set ts=4 sw=4 expandtab: */

kc3-lang/SDL/src/atomic/SDL_spinlock.c

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kc3-lang/SDL /src/atomic/SDL_spinlock.c