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| author | Yann Ylavic <ylavic@apache.org> | 2023-02-09 13:36:18 +0000 |
|---|---|---|
| committer | Yann Ylavic <ylavic@apache.org> | 2023-02-09 13:36:18 +0000 |
| commit | c0cce761f8e04183ddd506bdb814d66bab5f4a78 (patch) | |
| tree | f78eabc76f55a1085e8836c1f484a3516309df9e | |
| parent | 8c6a1aa1fa33f8c82d1333c9ef38c09799b4cf7b (diff) | |
| download | apr-c0cce761f8e04183ddd506bdb814d66bab5f4a78.tar.gz | |
apr_atomic: Generic apr_atomic_read64() needs a mutex on 32bit systems (tearing).
A 64bit load on a 32 bit CPU/system uses two instructions (tearing), so ensure
atomicity with regard to other atomic functions by using the (same) lock.
test_atomics_threaded_setread64() fails because of this on 32bit systems. PR 66457.
* atomic/unix/mutex64.c(apr_atomic_read64):
Use locking when APR_SIZEOF_VOIDP < 8
git-svn-id: https://svn.apache.org/repos/asf/apr/apr/trunk@1907541 13f79535-47bb-0310-9956-ffa450edef68
| -rw-r--r-- | atomic/unix/mutex64.c | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/atomic/unix/mutex64.c b/atomic/unix/mutex64.c index 9fc44af61..9f1f1df6d 100644 --- a/atomic/unix/mutex64.c +++ b/atomic/unix/mutex64.c @@ -96,7 +96,26 @@ apr_status_t apr__atomic_generic64_init(apr_pool_t *p) APR_DECLARE(apr_uint64_t) apr_atomic_read64(volatile apr_uint64_t *mem) { + /* On 32bit CPUs this loads with two instructions (tearing), + * so a lock is needed to ensure atomicity. + * + * APR_SIZEOF_VOIDP is probably not the right check for 32 vs 64 bits CPUs + * but it spares an (hardly-)exhaustive list of supported CPUs (and using + * assembly). If APR_SIZEOF_VOIDP==4 means that the compiler generates + * 32bit instructions (-m32 or whatever) then it's the right check though. + */ +#if APR_SIZEOF_VOIDP >= 8 return *mem; +#else + apr_uint64_t cur_value; + DECLARE_MUTEX_LOCKED(mutex, mem); + + cur_value = *mem; + + MUTEX_UNLOCK(mutex); + + return cur_value; +#endif } APR_DECLARE(void) apr_atomic_set64(volatile apr_uint64_t *mem, apr_uint64_t val) |