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2a5bf96891
This is the most trivial (but also most efficient) implementation possible. Should be good enough for now.
60 lines
1.9 KiB
C
60 lines
1.9 KiB
C
/*
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* PROJECT: ReactOS CRT library
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* LICENSE: CC0-1.0 (https://spdx.org/licenses/CC0-1.0)
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* PURPOSE: Thread safe initialization support routines for MSVC and Clang-CL
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* COPYRIGHT: Copyright 2019 Timo Kreuzer (timo.kreuzer@reactos.org)
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*/
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#include <intrin.h>
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int _stdcall SwitchToThread(void);
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unsigned int _tls_array;
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unsigned int _tls_index;
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long _Init_global_epoch;
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long _Init_thread_epoch;
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/*
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This function tries to acquire a lock on the initialization for the static
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variable by changing the value saved in *ptss to -1. If *ptss is 0, the
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variable was not initialized yet and the function tries to set it to -1.
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If that succeeds, the function will return. If the value is already -1,
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another thread is in the process of doing the initialization and we
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wait for it. If it is any other value the initialization is complete.
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After returning the compiler generated code will check the value:
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if it is -1 it will continue with the initialization, otherwise the
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initialization must be complete and will be skipped.
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*/
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void
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_Init_thread_header(volatile int* ptss)
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{
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while (1)
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{
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/* Try to acquire the first initialization lock */
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int oldTss = _InterlockedCompareExchange((long*)ptss, -1, 0);
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if (oldTss == -1)
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{
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/* Busy, wait for the other thread to do the initialization */
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SwitchToThread();
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continue;
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}
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/* Either we acquired the lock and the caller will do the initializaion
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or the initialization is complete and the caller will skip it */
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break;
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}
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}
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void
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_Init_thread_footer(volatile int* ptss)
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{
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/* Initialization is complete */
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*ptss = _InterlockedIncrement(&_Init_global_epoch);
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}
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void
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_Init_thread_abort(volatile int* ptss)
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{
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/* Abort the initialization */
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_InterlockedAnd((volatile long*)ptss, 0);
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}
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