reactos/sdk/lib/crt/startup/threadSafeInit.c
Timo Kreuzer 2a5bf96891 [CRT] Implement thread/fiber safe support for MSVC and Clang-CL
This is the most trivial (but also most efficient) implementation possible. Should be good enough for now.
2019-02-12 19:31:33 +01:00

61 lines
1.9 KiB
C

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