dlls/ntdll/critsection.c

   1 /*
   2  * Win32 critical sections
   3  *
   4  * Copyright 1998 Alexandre Julliard
   5  *
   6  * This library is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU Lesser General Public
   8  * License as published by the Free Software Foundation; either
   9  * version 2.1 of the License, or (at your option) any later version.
  10  *
  11  * This library is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14  * Lesser General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU Lesser General Public
  17  * License along with this library; if not, write to the Free Software
  18  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
  19  */
  20
  21 #include "config.h"
  22 #include "wine/port.h"
  23
  24 #include <assert.h>
  25 #include <errno.h>
  26 #include <stdarg.h>
  27 #include <stdio.h>
  28 #include <sys/types.h>
  29 #ifdef HAVE_SYS_SYSCALL_H
  30 #include <sys/syscall.h>
  31 #endif
  32 #include <time.h>
  33 #include "ntstatus.h"
  34 #define WIN32_NO_STATUS
  35 #include "windef.h"
  36 #include "winternl.h"
  37 #include "wine/debug.h"
  38 #include "ntdll_misc.h"
  39
  40 WINE_DEFAULT_DEBUG_CHANNEL(ntdll);
  41 WINE_DECLARE_DEBUG_CHANNEL(relay);
  42
  43 static inline LONG interlocked_inc( PLONG dest )
  44 {
  45     return interlocked_xchg_add( dest, 1 ) + 1;
  46 }
  47
  48 static inline LONG interlocked_dec( PLONG dest )
  49 {
  50     return interlocked_xchg_add( dest, -1 ) - 1;
  51 }
  52
  53 static inline void small_pause(void)
  54 {
  55 #ifdef __i386__
  56     __asm__ __volatile__( "rep;nop" : : : "memory" );
  57 #else
  58     __asm__ __volatile__( "" : : : "memory" );
  59 #endif
  60 }
  61
  62 #ifdef __linux__
  63
  64 static inline int futex_wait( int *addr, int val, struct timespec *timeout )
  65 {
  66     return syscall( SYS_futex, addr, 0/*FUTEX_WAIT*/, val, timeout, 0, 0 );
  67 }
  68
  69 static inline int futex_wake( int *addr, int val )
  70 {
  71     return syscall( SYS_futex, addr, 1/*FUTEX_WAKE*/, val, NULL, 0, 0 );
  72 }
  73
  74 static inline int use_futexes(void)
  75 {
  76     static int supported = -1;
  77
  78     if (supported == -1)
  79     {
  80         futex_wait( &supported, 10, NULL );
  81         supported = (errno != ENOSYS);
  82     }
  83     return supported;
  84 }
  85
  86 static inline NTSTATUS fast_wait( RTL_CRITICAL_SECTION *crit, int timeout )
  87 {
  88     int val;
  89     struct timespec timespec;
  90
  91     if (!use_futexes()) return STATUS_NOT_IMPLEMENTED;
  92
  93     timespec.tv_sec  = timeout;
  94     timespec.tv_nsec = 0;
  95     while ((val = interlocked_cmpxchg( (int *)&crit->LockSemaphore, 0, 1 )) != 1)
  96     {
  97         /* note: this may wait longer than specified in case of signals or */
  98         /*       multiple wake-ups, but that shouldn't be a problem */
  99         if (futex_wait( (int *)&crit->LockSemaphore, val, &timespec ) == -1 && errno == ETIMEDOUT)
 100             return STATUS_TIMEOUT;
 101     }
 102     return STATUS_WAIT_0;
 103 }
 104
 105 static inline NTSTATUS fast_wake( RTL_CRITICAL_SECTION *crit )
 106 {
 107     if (!use_futexes()) return STATUS_NOT_IMPLEMENTED;
 108
 109     *(int *)&crit->LockSemaphore = 1;
 110     futex_wake( (int *)&crit->LockSemaphore, 1 );
 111     return STATUS_SUCCESS;
 112 }
 113
 114 static inline void close_semaphore( RTL_CRITICAL_SECTION *crit )
 115 {
 116     if (!use_futexes()) NtClose( crit->LockSemaphore );
 117 }
 118
 119 #elif defined(__APPLE__)
 120
 121 #include <mach/mach.h>
 122 #include <mach/task.h>
 123 #include <mach/semaphore.h>
 124
 125 static inline semaphore_t get_mach_semaphore( RTL_CRITICAL_SECTION *crit )
 126 {
 127     semaphore_t ret = *(int *)&crit->LockSemaphore;
 128     if (!ret)
 129     {
 130         semaphore_t sem;
 131         if (semaphore_create( mach_task_self(), &sem, SYNC_POLICY_FIFO, 0 )) return 0;
 132         if (!(ret = interlocked_cmpxchg( (int *)&crit->LockSemaphore, sem, 0 )))
 133             ret = sem;
 134         else
 135             semaphore_destroy( mach_task_self(), sem );  /* somebody beat us to it */
 136     }
 137     return ret;
 138 }
 139
 140 static inline NTSTATUS fast_wait( RTL_CRITICAL_SECTION *crit, int timeout )
 141 {
 142     mach_timespec_t timespec;
 143     semaphore_t sem = get_mach_semaphore( crit );
 144
 145     timespec.tv_sec = timeout;
 146     timespec.tv_nsec = 0;
 147     for (;;)
 148     {
 149         switch( semaphore_timedwait( sem, timespec ))
 150         {
 151         case KERN_SUCCESS:
 152             return STATUS_WAIT_0;
 153         case KERN_ABORTED:
 154             continue;  /* got a signal, restart */
 155         case KERN_OPERATION_TIMED_OUT:
 156             return STATUS_TIMEOUT;
 157         default:
 158             return STATUS_INVALID_HANDLE;
 159         }
 160     }
 161 }
 162
 163 static inline NTSTATUS fast_wake( RTL_CRITICAL_SECTION *crit )
 164 {
 165     semaphore_t sem = get_mach_semaphore( crit );
 166     semaphore_signal( sem );
 167     return STATUS_SUCCESS;
 168 }
 169
 170 static inline void close_semaphore( RTL_CRITICAL_SECTION *crit )
 171 {
 172     semaphore_destroy( mach_task_self(), *(int *)&crit->LockSemaphore );
 173 }
 174
 175 #else  /* __APPLE__ */
 176
 177 static inline NTSTATUS fast_wait( RTL_CRITICAL_SECTION *crit, int timeout )
 178 {
 179     return STATUS_NOT_IMPLEMENTED;
 180 }
 181
 182 static inline NTSTATUS fast_wake( RTL_CRITICAL_SECTION *crit )
 183 {
 184     return STATUS_NOT_IMPLEMENTED;
 185 }
 186
 187 static inline void close_semaphore( RTL_CRITICAL_SECTION *crit )
 188 {
 189     NtClose( crit->LockSemaphore );
 190 }
 191
 192 #endif
 193
 194 /***********************************************************************
 195  *           get_semaphore
 196  */
 197 static inline HANDLE get_semaphore( RTL_CRITICAL_SECTION *crit )
 198 {
 199     HANDLE ret = crit->LockSemaphore;
 200     if (!ret)
 201     {
 202         HANDLE sem;
 203         if (NtCreateSemaphore( &sem, SEMAPHORE_ALL_ACCESS, NULL, 0, 1 )) return 0;
 204         if (!(ret = interlocked_cmpxchg_ptr( &crit->LockSemaphore, sem, 0 )))
 205             ret = sem;
 206         else
 207             NtClose(sem);  /* somebody beat us to it */
 208     }
 209     return ret;
 210 }
 211
 212 /***********************************************************************
 213  *           wait_semaphore
 214  */
 215 static inline NTSTATUS wait_semaphore( RTL_CRITICAL_SECTION *crit, int timeout )
 216 {
 217     NTSTATUS ret;
 218
 219     /* debug info is cleared by MakeCriticalSectionGlobal */
 220     if (!crit->DebugInfo || ((ret = fast_wait( crit, timeout )) == STATUS_NOT_IMPLEMENTED))
 221     {
 222         HANDLE sem = get_semaphore( crit );
 223         LARGE_INTEGER time;
 224
 225         time.QuadPart = timeout * (LONGLONG)-10000000;
 226         ret = NTDLL_wait_for_multiple_objects( 1, &sem, 0, &time, 0 );
 227     }
 228     return ret;
 229 }
 230
 231 /***********************************************************************
 232  *           RtlInitializeCriticalSection   (NTDLL.@)
 233  *
 234  * Initialises a new critical section.
 235  *
 236  * PARAMS
 237  *  crit [O] Critical section to initialise
 238  *
 239  * RETURNS
 240  *  STATUS_SUCCESS.
 241  *
 242  * SEE
 243  *  RtlInitializeCriticalSectionEx(),
 244  *  RtlInitializeCriticalSectionAndSpinCount(), RtlDeleteCriticalSection(),
 245  *  RtlEnterCriticalSection(), RtlLeaveCriticalSection(),
 246  *  RtlTryEnterCriticalSection(), RtlSetCriticalSectionSpinCount()
 247  */
 248 NTSTATUS WINAPI RtlInitializeCriticalSection( RTL_CRITICAL_SECTION *crit )
 249 {
 250     return RtlInitializeCriticalSectionEx( crit, 0, 0 );
 251 }
 252
 253 /***********************************************************************
 254  *           RtlInitializeCriticalSectionAndSpinCount   (NTDLL.@)
 255  *
 256  * Initialises a new critical section with a given spin count.
 257  *
 258  * PARAMS
 259  *   crit      [O] Critical section to initialise
 260  *   spincount [I] Spin count for crit
 261  *
 262  * RETURNS
 263  *  STATUS_SUCCESS.
 264  *
 265  * NOTES
 266  *  Available on NT4 SP3 or later.
 267  *
 268  * SEE
 269  *  RtlInitializeCriticalSectionEx(),
 270  *  RtlInitializeCriticalSection(), RtlDeleteCriticalSection(),
 271  *  RtlEnterCriticalSection(), RtlLeaveCriticalSection(),
 272  *  RtlTryEnterCriticalSection(), RtlSetCriticalSectionSpinCount()
 273  */
 274 NTSTATUS WINAPI RtlInitializeCriticalSectionAndSpinCount( RTL_CRITICAL_SECTION *crit, ULONG spincount )
 275 {
 276     return RtlInitializeCriticalSectionEx( crit, spincount, 0 );
 277 }
 278
 279 /***********************************************************************
 280  *           RtlInitializeCriticalSectionEx   (NTDLL.@)
 281  *
 282  * Initialises a new critical section with a given spin count and flags.
 283  *
 284  * PARAMS
 285  *   crit      [O] Critical section to initialise.
 286  *   spincount [I] Number of times to spin upon contention.
 287  *   flags     [I] RTL_CRITICAL_SECTION_FLAG_ flags from winnt.h.
 288  *
 289  * RETURNS
 290  *  STATUS_SUCCESS.
 291  *
 292  * NOTES
 293  *  Available on Vista or later.
 294  *
 295  * SEE
 296  *  RtlInitializeCriticalSection(), RtlDeleteCriticalSection(),
 297  *  RtlEnterCriticalSection(), RtlLeaveCriticalSection(),
 298  *  RtlTryEnterCriticalSection(), RtlSetCriticalSectionSpinCount()
 299  */
 300 NTSTATUS WINAPI RtlInitializeCriticalSectionEx( RTL_CRITICAL_SECTION *crit, ULONG spincount, ULONG flags )
 301 {
 302     if (flags & (RTL_CRITICAL_SECTION_FLAG_DYNAMIC_SPIN|RTL_CRITICAL_SECTION_FLAG_STATIC_INIT))
 303         FIXME("(%p,%u,0x%08x) semi-stub\n", crit, spincount, flags);
 304
 305     /* FIXME: if RTL_CRITICAL_SECTION_FLAG_STATIC_INIT is given, we should use
 306      * memory from a static pool to hold the debug info. Then heap.c could pass
 307      * this flag rather than initialising the process heap CS by hand. If this
 308      * is done, then debug info should be managed through Rtlp[Allocate|Free]DebugInfo
 309      * so (e.g.) MakeCriticalSectionGlobal() doesn't free it using HeapFree().
 310      */
 311     if (flags & RTL_CRITICAL_SECTION_FLAG_NO_DEBUG_INFO)
 312         crit->DebugInfo = NULL;
 313     else
 314         crit->DebugInfo = RtlAllocateHeap(GetProcessHeap(), 0, sizeof(RTL_CRITICAL_SECTION_DEBUG));
 315
 316     if (crit->DebugInfo)
 317     {
 318         crit->DebugInfo->Type = 0;
 319         crit->DebugInfo->CreatorBackTraceIndex = 0;
 320         crit->DebugInfo->CriticalSection = crit;
 321         crit->DebugInfo->ProcessLocksList.Blink = &(crit->DebugInfo->ProcessLocksList);
 322         crit->DebugInfo->ProcessLocksList.Flink = &(crit->DebugInfo->ProcessLocksList);
 323         crit->DebugInfo->EntryCount = 0;
 324         crit->DebugInfo->ContentionCount = 0;
 325         memset( crit->DebugInfo->Spare, 0, sizeof(crit->DebugInfo->Spare) );
 326     }
 327     crit->LockCount      = -1;
 328     crit->RecursionCount = 0;
 329     crit->OwningThread   = 0;
 330     crit->LockSemaphore  = 0;
 331     if (NtCurrentTeb()->Peb->NumberOfProcessors <= 1) spincount = 0;
 332     crit->SpinCount = spincount & ~0x80000000;
 333     return STATUS_SUCCESS;
 334 }
 335
 336 /***********************************************************************
 337  *           RtlSetCriticalSectionSpinCount   (NTDLL.@)
 338  *
 339  * Sets the spin count of a critical section.
 340  *
 341  * PARAMS
 342  *   crit      [I/O] Critical section
 343  *   spincount [I] Spin count for crit
 344  *
 345  * RETURNS
 346  *  The previous spin count.
 347  *
 348  * NOTES
 349  *  If the system is not SMP, spincount is ignored and set to 0.
 350  *
 351  * SEE
 352  *  RtlInitializeCriticalSectionEx(),
 353  *  RtlInitializeCriticalSection(), RtlInitializeCriticalSectionAndSpinCount(),
 354  *  RtlDeleteCriticalSection(), RtlEnterCriticalSection(),
 355  *  RtlLeaveCriticalSection(), RtlTryEnterCriticalSection()
 356  */
 357 ULONG WINAPI RtlSetCriticalSectionSpinCount( RTL_CRITICAL_SECTION *crit, ULONG spincount )
 358 {
 359     ULONG oldspincount = crit->SpinCount;
 360     if (NtCurrentTeb()->Peb->NumberOfProcessors <= 1) spincount = 0;
 361     crit->SpinCount = spincount;
 362     return oldspincount;
 363 }
 364
 365 /***********************************************************************
 366  *           RtlDeleteCriticalSection   (NTDLL.@)
 367  *
 368  * Frees the resources used by a critical section.
 369  *
 370  * PARAMS
 371  *  crit [I/O] Critical section to free
 372  *
 373  * RETURNS
 374  *  STATUS_SUCCESS.
 375  *
 376  * SEE
 377  *  RtlInitializeCriticalSectionEx(),
 378  *  RtlInitializeCriticalSection(), RtlInitializeCriticalSectionAndSpinCount(),
 379  *  RtlDeleteCriticalSection(), RtlEnterCriticalSection(),
 380  *  RtlLeaveCriticalSection(), RtlTryEnterCriticalSection()
 381  */
 382 NTSTATUS WINAPI RtlDeleteCriticalSection( RTL_CRITICAL_SECTION *crit )
 383 {
 384     crit->LockCount      = -1;
 385     crit->RecursionCount = 0;
 386     crit->OwningThread   = 0;
 387     if (crit->DebugInfo)
 388     {
 389         /* only free the ones we made in here */
 390         if (!crit->DebugInfo->Spare[0])
 391         {
 392             RtlFreeHeap( GetProcessHeap(), 0, crit->DebugInfo );
 393             crit->DebugInfo = NULL;
 394         }
 395         close_semaphore( crit );
 396     }
 397     else NtClose( crit->LockSemaphore );
 398     crit->LockSemaphore = 0;
 399     return STATUS_SUCCESS;
 400 }
 401
 402
 403 /***********************************************************************
 404  *           RtlpWaitForCriticalSection   (NTDLL.@)
 405  *
 406  * Waits for a busy critical section to become free.
 407  *
 408  * PARAMS
 409  *  crit [I/O] Critical section to wait for
 410  *
 411  * RETURNS
 412  *  STATUS_SUCCESS.
 413  *
 414  * NOTES
 415  *  Use RtlEnterCriticalSection() instead of this function as it is often much
 416  *  faster.
 417  *
 418  * SEE
 419  *  RtlInitializeCriticalSectionEx(),
 420  *  RtlInitializeCriticalSection(), RtlInitializeCriticalSectionAndSpinCount(),
 421  *  RtlDeleteCriticalSection(), RtlEnterCriticalSection(),
 422  *  RtlLeaveCriticalSection(), RtlTryEnterCriticalSection()
 423  */
 424 NTSTATUS WINAPI RtlpWaitForCriticalSection( RTL_CRITICAL_SECTION *crit )
 425 {
 426     for (;;)
 427     {
 428         EXCEPTION_RECORD rec;
 429         NTSTATUS status = wait_semaphore( crit, 5 );
 430
 431         if ( status == STATUS_TIMEOUT )
 432         {
 433             const char *name = NULL;
 434             if (crit->DebugInfo) name = (char *)crit->DebugInfo->Spare[0];
 435             if (!name) name = "?";
 436             ERR( "section %p %s wait timed out in thread %04x, blocked by %04x, retrying (60 sec)\n",
 437                  crit, debugstr_a(name), GetCurrentThreadId(), HandleToULong(crit->OwningThread) );
 438             status = wait_semaphore( crit, 60 );
 439             if ( status == STATUS_TIMEOUT && TRACE_ON(relay) )
 440             {
 441                 ERR( "section %p %s wait timed out in thread %04x, blocked by %04x, retrying (5 min)\n",
 442                      crit, debugstr_a(name), GetCurrentThreadId(), HandleToULong(crit->OwningThread) );
 443                 status = wait_semaphore( crit, 300 );
 444             }
 445         }
 446         if (status == STATUS_WAIT_0) break;
 447
 448         /* Throw exception only for Wine internal locks */
 449         if ((!crit->DebugInfo) || (!crit->DebugInfo->Spare[0])) continue;
 450
 451         rec.ExceptionCode    = STATUS_POSSIBLE_DEADLOCK;
 452         rec.ExceptionFlags   = 0;
 453         rec.ExceptionRecord  = NULL;
 454         rec.ExceptionAddress = RtlRaiseException;  /* sic */
 455         rec.NumberParameters = 1;
 456         rec.ExceptionInformation[0] = (ULONG_PTR)crit;
 457         RtlRaiseException( &rec );
 458     }
 459     if (crit->DebugInfo) crit->DebugInfo->ContentionCount++;
 460     return STATUS_SUCCESS;
 461 }
 462
 463
 464 /***********************************************************************
 465  *           RtlpUnWaitCriticalSection   (NTDLL.@)
 466  *
 467  * Notifies other threads waiting on the busy critical section that it has
 468  * become free.
 469  *
 470  * PARAMS
 471  *  crit [I/O] Critical section
 472  *
 473  * RETURNS
 474  *  Success: STATUS_SUCCESS.
 475  *  Failure: Any error returned by NtReleaseSemaphore()
 476  *
 477  * NOTES
 478  *  Use RtlLeaveCriticalSection() instead of this function as it is often much
 479  *  faster.
 480  *
 481  * SEE
 482  *  RtlInitializeCriticalSectionEx(),
 483  *  RtlInitializeCriticalSection(), RtlInitializeCriticalSectionAndSpinCount(),
 484  *  RtlDeleteCriticalSection(), RtlEnterCriticalSection(),
 485  *  RtlLeaveCriticalSection(), RtlTryEnterCriticalSection()
 486  */
 487 NTSTATUS WINAPI RtlpUnWaitCriticalSection( RTL_CRITICAL_SECTION *crit )
 488 {
 489     NTSTATUS ret;
 490
 491     /* debug info is cleared by MakeCriticalSectionGlobal */
 492     if (!crit->DebugInfo || ((ret = fast_wake( crit )) == STATUS_NOT_IMPLEMENTED))
 493     {
 494         HANDLE sem = get_semaphore( crit );
 495         ret = NtReleaseSemaphore( sem, 1, NULL );
 496     }
 497     if (ret) RtlRaiseStatus( ret );
 498     return ret;
 499 }
 500
 501
 502 /***********************************************************************
 503  *           RtlEnterCriticalSection   (NTDLL.@)
 504  *
 505  * Enters a critical section, waiting for it to become available if necessary.
 506  *
 507  * PARAMS
 508  *  crit [I/O] Critical section to enter
 509  *
 510  * RETURNS
 511  *  STATUS_SUCCESS. The critical section is held by the caller.
 512  *
 513  * SEE
 514  *  RtlInitializeCriticalSectionEx(),
 515  *  RtlInitializeCriticalSection(), RtlInitializeCriticalSectionAndSpinCount(),
 516  *  RtlDeleteCriticalSection(), RtlSetCriticalSectionSpinCount(),
 517  *  RtlLeaveCriticalSection(), RtlTryEnterCriticalSection()
 518  */
 519 NTSTATUS WINAPI RtlEnterCriticalSection( RTL_CRITICAL_SECTION *crit )
 520 {
 521     if (crit->SpinCount)
 522     {
 523         ULONG count;
 524
 525         if (RtlTryEnterCriticalSection( crit )) return STATUS_SUCCESS;
 526         for (count = crit->SpinCount; count > 0; count--)
 527         {
 528             if (crit->LockCount > 0) break;  /* more than one waiter, don't bother spinning */
 529             if (crit->LockCount == -1)       /* try again */
 530             {
 531                 if (interlocked_cmpxchg( &crit->LockCount, 0, -1 ) == -1) goto done;
 532             }
 533             small_pause();
 534         }
 535     }
 536
 537     if (interlocked_inc( &crit->LockCount ))
 538     {
 539         if (crit->OwningThread == ULongToHandle(GetCurrentThreadId()))
 540         {
 541             crit->RecursionCount++;
 542             return STATUS_SUCCESS;
 543         }
 544
 545         /* Now wait for it */
 546         RtlpWaitForCriticalSection( crit );
 547     }
 548 done:
 549     crit->OwningThread   = ULongToHandle(GetCurrentThreadId());
 550     crit->RecursionCount = 1;
 551     return STATUS_SUCCESS;
 552 }
 553
 554
 555 /***********************************************************************
 556  *           RtlTryEnterCriticalSection   (NTDLL.@)
 557  *
 558  * Tries to enter a critical section without waiting.
 559  *
 560  * PARAMS
 561  *  crit [I/O] Critical section to enter
 562  *
 563  * RETURNS
 564  *  Success: TRUE. The critical section is held by the caller.
 565  *  Failure: FALSE. The critical section is currently held by another thread.
 566  *
 567  * SEE
 568  *  RtlInitializeCriticalSectionEx(),
 569  *  RtlInitializeCriticalSection(), RtlInitializeCriticalSectionAndSpinCount(),
 570  *  RtlDeleteCriticalSection(), RtlEnterCriticalSection(),
 571  *  RtlLeaveCriticalSection(), RtlSetCriticalSectionSpinCount()
 572  */
 573 BOOL WINAPI RtlTryEnterCriticalSection( RTL_CRITICAL_SECTION *crit )
 574 {
 575     BOOL ret = FALSE;
 576     if (interlocked_cmpxchg( &crit->LockCount, 0, -1 ) == -1)
 577     {
 578         crit->OwningThread   = ULongToHandle(GetCurrentThreadId());
 579         crit->RecursionCount = 1;
 580         ret = TRUE;
 581     }
 582     else if (crit->OwningThread == ULongToHandle(GetCurrentThreadId()))
 583     {
 584         interlocked_inc( &crit->LockCount );
 585         crit->RecursionCount++;
 586         ret = TRUE;
 587     }
 588     return ret;
 589 }
 590
 591
 592 /***********************************************************************
 593  *           RtlLeaveCriticalSection   (NTDLL.@)
 594  *
 595  * Leaves a critical section.
 596  *
 597  * PARAMS
 598  *  crit [I/O] Critical section to leave.
 599  *
 600  * RETURNS
 601  *  STATUS_SUCCESS.
 602  *
 603  * SEE
 604  *  RtlInitializeCriticalSectionEx(),
 605  *  RtlInitializeCriticalSection(), RtlInitializeCriticalSectionAndSpinCount(),
 606  *  RtlDeleteCriticalSection(), RtlEnterCriticalSection(),
 607  *  RtlSetCriticalSectionSpinCount(), RtlTryEnterCriticalSection()
 608  */
 609 NTSTATUS WINAPI RtlLeaveCriticalSection( RTL_CRITICAL_SECTION *crit )
 610 {
 611     if (--crit->RecursionCount) interlocked_dec( &crit->LockCount );
 612     else
 613     {
 614         crit->OwningThread = 0;
 615         if (interlocked_dec( &crit->LockCount ) >= 0)
 616         {
 617             /* someone is waiting */
 618             RtlpUnWaitCriticalSection( crit );
 619         }
 620     }
 621     return STATUS_SUCCESS;
 622 }