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Thread safe crc32 table initialization

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The lazy generated table was not entirely thread safe under the
C++ (11) memory model, as pointed out by TSAN.

Bug: webrtc:10627
Change-Id: I0fe1cc7c10ca218a92c710a6382b64d7827f3a6a
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/136980
Reviewed-by: Amit Hilbuch <amithi@webrtc.org>
Commit-Queue: Steve Anton <steveanton@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27954}
This commit is contained in:
Steve Anton 2019-05-15 16:22:38 -07:00 committed by Commit Bot
parent 9a7970de28
commit 0f1a7ba23c
1 changed files with 4 additions and 5 deletions
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9
rtc_base/crc32.cc
View file

@ -19,11 +19,9 @@ namespace rtc {
// CRC32 polynomial, in reversed form.
// See RFC 1952, or http://en.wikipedia.org/wiki/Cyclic_redundancy_check
static const uint32_t kCrc32Polynomial = 0xEDB88320;
static uint32_t kCrc32Table[256] = {0};
static void EnsureCrc32TableInited() {
if (kCrc32Table[arraysize(kCrc32Table) - 1])
return; // already inited
static uint32_t* LoadCrc32Table() {
static uint32_t kCrc32Table[256];
for (uint32_t i = 0; i < arraysize(kCrc32Table); ++i) {
uint32_t c = i;
for (size_t j = 0; j < 8; ++j) {
@ -35,10 +33,11 @@ static void EnsureCrc32TableInited() {
}
kCrc32Table[i] = c;
}
return kCrc32Table;
}
uint32_t UpdateCrc32(uint32_t start, const void* buf, size_t len) {
EnsureCrc32TableInited();
static uint32_t* kCrc32Table = LoadCrc32Table();
uint32_t c = start ^ 0xFFFFFFFF;
const uint8_t* u = static_cast<const uint8_t*>(buf);