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* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* This source file is part of SableVM. *
* *
* See the file "LICENSE" for the copyright information and for *
* the terms and conditions for copying, distribution and *
* modification of this source file. *
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
*** Ideas about POSIX Compare & Swap ***
NOTE: These ideas and code snippets have not been tested at all; not even
compiled. All such ugly (because almost surely slow) code (including the
two global mutexes) should NOT be compiled on an arch that has a better
implementation of these functions. => use #ifdef ...
IDEA: We could write the POSIX-only CAS. It's ugly, from a performance point
of view. To be avoided at almost any cost. Useful for blind porting, quite
temporarily.
CAS implementation should look like:
1. get POSIX lock (maybe by spin-locking)
2. do comparison and potential swap operation (non-atomically, in plain C)
3. release POSIX lock
4. end of CAS.
pthread_mutex_t _svmv_dummy_compare_and_swap_mutex;
static inline jboolean
_svmh_compare_and_swap (volatile _svmt_word *pword, _svmt_word old_value,
_svmt_word new_value)
{
jboolean result;
_svmm_mutex_lock (_svmv_dummy_compare_and_swap_mutex);
if (*pword == old_value)
{
*pword = new_value;
result = 1;
}
else
{
result = 0;
}
_svmm_mutex_unlock ();
return result;
}
Note: You must initialize _svmv_dummy_compare_and_swap_mutex in lib_init.c
with the instruction:
_svmm_mutex_init (_svmv_dummy_compare_and_swap_mutex);
In fact, you should put this code in some _svmf_system_init() function
(within system.c), then call this function within
_svmf_internal_init() of lib_init.c
so as to follow the current convention for *one time* initializations.
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