1 /* 2 * PROJECT: ReactOS CRT library 3 * LICENSE: CC0-1.0 (https://spdx.org/licenses/CC0-1.0) 4 * PURPOSE: Thread safe initialization support routines for MSVC and Clang-CL 5 * COPYRIGHT: Copyright 2019 Timo Kreuzer (timo.kreuzer@reactos.org) 6 */ 7 8 #include <intrin.h> 9 10 int _stdcall SwitchToThread(void); 11 12 unsigned int _tls_array; 13 unsigned int _tls_index; 14 long _Init_global_epoch; 15 long _Init_thread_epoch; 16 17 /* 18 This function tries to acquire a lock on the initialization for the static 19 variable by changing the value saved in *ptss to -1. If *ptss is 0, the 20 variable was not initialized yet and the function tries to set it to -1. 21 If that succeeds, the function will return. If the value is already -1, 22 another thread is in the process of doing the initialization and we 23 wait for it. If it is any other value the initialization is complete. 24 After returning the compiler generated code will check the value: 25 if it is -1 it will continue with the initialization, otherwise the 26 initialization must be complete and will be skipped. 27 */ 28 void 29 _Init_thread_header(volatile int* ptss) 30 { 31 while (1) 32 { 33 /* Try to acquire the first initialization lock */ 34 int oldTss = _InterlockedCompareExchange((long*)ptss, -1, 0); 35 if (oldTss == -1) 36 { 37 /* Busy, wait for the other thread to do the initialization */ 38 SwitchToThread(); 39 continue; 40 } 41 42 /* Either we acquired the lock and the caller will do the initializaion 43 or the initialization is complete and the caller will skip it */ 44 break; 45 } 46 } 47 48 void 49 _Init_thread_footer(volatile int* ptss) 50 { 51 /* Initialization is complete */ 52 *ptss = _InterlockedIncrement(&_Init_global_epoch); 53 } 54 55 void 56 _Init_thread_abort(volatile int* ptss) 57 { 58 /* Abort the initialization */ 59 _InterlockedAnd((volatile long*)ptss, 0); 60 } 61