src/atomic/SDL_spinlock.c
author Sam Lantinga <slouken@libsdl.org>
Mon, 07 Jul 2014 21:27:42 -0700
changeset 8991 13b0df1793e8
parent 8979 1e283b7a1580
child 9619 b94b6d0bff0f
permissions -rw-r--r--
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.
     1 /*
     2   Simple DirectMedia Layer
     3   Copyright (C) 1997-2014 Sam Lantinga <slouken@libsdl.org>
     4 
     5   This software is provided 'as-is', without any express or implied
     6   warranty.  In no event will the authors be held liable for any damages
     7   arising from the use of this software.
     8 
     9   Permission is granted to anyone to use this software for any purpose,
    10   including commercial applications, and to alter it and redistribute it
    11   freely, subject to the following restrictions:
    12 
    13   1. The origin of this software must not be misrepresented; you must not
    14      claim that you wrote the original software. If you use this software
    15      in a product, an acknowledgment in the product documentation would be
    16      appreciated but is not required.
    17   2. Altered source versions must be plainly marked as such, and must not be
    18      misrepresented as being the original software.
    19   3. This notice may not be removed or altered from any source distribution.
    20 */
    21 #include "../SDL_internal.h"
    22 
    23 #if defined(__WIN32__) || defined(__WINRT__)
    24 #include "../core/windows/SDL_windows.h"
    25 #endif
    26 
    27 #include "SDL_atomic.h"
    28 #include "SDL_mutex.h"
    29 #include "SDL_timer.h"
    30 
    31 #if !defined(HAVE_GCC_ATOMICS) && defined(__SOLARIS__)
    32 #include <atomic.h>
    33 #endif
    34 
    35 /* This function is where all the magic happens... */
    36 SDL_bool
    37 SDL_AtomicTryLock(SDL_SpinLock *lock)
    38 {
    39 #if SDL_ATOMIC_DISABLED
    40     /* Terrible terrible damage */
    41     static SDL_mutex *_spinlock_mutex;
    42 
    43     if (!_spinlock_mutex) {
    44         /* Race condition on first lock... */
    45         _spinlock_mutex = SDL_CreateMutex();
    46     }
    47     SDL_LockMutex(_spinlock_mutex);
    48     if (*lock == 0) {
    49         *lock = 1;
    50         SDL_UnlockMutex(_spinlock_mutex);
    51         return SDL_TRUE;
    52     } else {
    53         SDL_UnlockMutex(_spinlock_mutex);
    54         return SDL_FALSE;
    55     }
    56 
    57 #elif defined(_MSC_VER)
    58     SDL_COMPILE_TIME_ASSERT(locksize, sizeof(*lock) == sizeof(long));
    59     return (InterlockedExchange((long*)lock, 1) == 0);
    60 
    61 #elif HAVE_GCC_ATOMICS || HAVE_GCC_SYNC_LOCK_TEST_AND_SET
    62     return (__sync_lock_test_and_set(lock, 1) == 0);
    63 
    64 #elif defined(__GNUC__) && defined(__arm__) && \
    65         (defined(__ARM_ARCH_4__) || defined(__ARM_ARCH_4T__) || \
    66          defined(__ARM_ARCH_5__) || defined(__ARM_ARCH_5TE__) || \
    67          defined(__ARM_ARCH_5TEJ__))
    68     int result;
    69     __asm__ __volatile__ (
    70         "swp %0, %1, [%2]\n"
    71         : "=&r,&r" (result) : "r,0" (1), "r,r" (lock) : "memory");
    72     return (result == 0);
    73 
    74 #elif defined(__GNUC__) && defined(__arm__)
    75     int result;
    76     __asm__ __volatile__ (
    77         "ldrex %0, [%2]\nteq   %0, #0\nstrexeq %0, %1, [%2]"
    78         : "=&r" (result) : "r" (1), "r" (lock) : "cc", "memory");
    79     return (result == 0);
    80 
    81 #elif defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
    82     int result;
    83     __asm__ __volatile__(
    84         "lock ; xchgl %0, (%1)\n"
    85         : "=r" (result) : "r" (lock), "0" (1) : "cc", "memory");
    86     return (result == 0);
    87 
    88 #elif defined(__MACOSX__) || defined(__IPHONEOS__)
    89     /* Maybe used for PowerPC, but the Intel asm or gcc atomics are favored. */
    90     return OSAtomicCompareAndSwap32Barrier(0, 1, lock);
    91 
    92 #elif defined(__SOLARIS__) && defined(_LP64)
    93     /* Used for Solaris with non-gcc compilers. */
    94     return (SDL_bool) ((int) atomic_cas_64((volatile uint64_t*)lock, 0, 1) == 0);
    95 
    96 #elif defined(__SOLARIS__) && !defined(_LP64)
    97     /* Used for Solaris with non-gcc compilers. */
    98     return (SDL_bool) ((int) atomic_cas_32((volatile uint32_t*)lock, 0, 1) == 0);
    99 
   100 #else
   101 #error Please implement for your platform.
   102     return SDL_FALSE;
   103 #endif
   104 }
   105 
   106 void
   107 SDL_AtomicLock(SDL_SpinLock *lock)
   108 {
   109     /* FIXME: Should we have an eventual timeout? */
   110     while (!SDL_AtomicTryLock(lock)) {
   111         SDL_Delay(0);
   112     }
   113 }
   114 
   115 void
   116 SDL_AtomicUnlock(SDL_SpinLock *lock)
   117 {
   118 #if defined(_MSC_VER)
   119     _ReadWriteBarrier();
   120     *lock = 0;
   121 
   122 #elif HAVE_GCC_ATOMICS || HAVE_GCC_SYNC_LOCK_TEST_AND_SET
   123     __sync_lock_release(lock);
   124 
   125 #elif defined(__SOLARIS__)
   126     /* Used for Solaris when not using gcc. */
   127     *lock = 0;
   128     membar_producer();
   129 
   130 #else
   131     *lock = 0;
   132 #endif
   133 }
   134 
   135 /* vi: set ts=4 sw=4 expandtab: */