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Implemented exponential backoff for shared memory related waits

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Thulinma 2022-03-21 13:25:55 +01:00
parent 35a54dbd61
commit 9993dfafa2
3 changed files with 25 additions and 8 deletions
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16
lib/shared_memory.cpp
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@ -100,7 +100,7 @@ namespace IPC{
} }
if (!(*this)){ if (!(*this)){
if (GetLastError() == ERROR_FILE_NOT_FOUND && !noWait){// Error code 2 if (GetLastError() == ERROR_FILE_NOT_FOUND && !noWait){// Error code 2
Util::wait(500); Util::wait(Util::expBackoffMs(timer-1, 10, 5000));
}else{ }else{
break; break;
} }
@ -121,7 +121,7 @@ namespace IPC{
} }
if (!(*this)){ if (!(*this)){
if (errno == ENOENT && !noWait){ if (errno == ENOENT && !noWait){
Util::wait(500); Util::wait(Util::expBackoffMs(timer-1, 10, 5000));
}else{ }else{
break; break;
} }
@ -458,10 +458,10 @@ namespace IPC{
}else{ }else{
int i = 0; int i = 0;
do{ do{
if (i != 0){Util::wait(1000);} if (i != 0){Util::wait(Util::expBackoffMs(i-1, 10, 10000));}
handle = OpenFileMappingA(FILE_MAP_ALL_ACCESS, FALSE, name.c_str()); handle = OpenFileMappingA(FILE_MAP_ALL_ACCESS, FALSE, name.c_str());
i++; i++;
}while (i < 10 && !handle && autoBackoff); }while (i <= 10 && !handle && autoBackoff);
} }
if (!handle){ if (!handle){
MEDIUM_MSG("%s for page %s failed with error code %u", MEDIUM_MSG("%s for page %s failed with error code %u",
@ -489,9 +489,9 @@ namespace IPC{
handle = shm_open(name.c_str(), O_CREAT | O_RDWR, ACCESSPERMS); handle = shm_open(name.c_str(), O_CREAT | O_RDWR, ACCESSPERMS);
}else{ }else{
int i = 0; int i = 0;
while (i < 10 && handle == -1 && autoBackoff){ while (i < 11 && handle == -1 && autoBackoff){
i++; i++;
Util::wait(1000); Util::wait(Util::expBackoffMs(i-1, 10, 10000));
handle = shm_open(name.c_str(), O_RDWR, ACCESSPERMS); handle = shm_open(name.c_str(), O_RDWR, ACCESSPERMS);
} }
} }
@ -620,9 +620,9 @@ namespace IPC{
O_CREAT | O_TRUNC | O_RDWR, (mode_t)0600); O_CREAT | O_TRUNC | O_RDWR, (mode_t)0600);
}else{ }else{
int i = 0; int i = 0;
while (i < 10 && handle == -1 && autoBackoff){ while (i < 11 && handle == -1 && autoBackoff){
i++; i++;
Util::wait(1000); Util::wait(Util::expBackoffMs(i-1, 10, 10000));
handle = open(std::string(Util::getTmpFolder() + name).c_str(), O_RDWR, (mode_t)0600); handle = open(std::string(Util::getTmpFolder() + name).c_str(), O_RDWR, (mode_t)0600);
} }
} }

15
lib/util.cpp
View file

@ -149,6 +149,21 @@ namespace Util{
} }
} }
//Returns the time to wait in milliseconds for exponential back-off waiting.
//If currIter > maxIter, always returns 5ms to prevent tight eternal loops when mistakes are made
//Otherwise, exponentially increases wait time for a total of maxWait milliseconds after maxIter calls.
//Wildly inaccurate for very short max durations and/or very large maxIter values, but otherwise works as expected.
int64_t expBackoffMs(const size_t currIter, const size_t maxIter, const int64_t maxWait){
if (currIter > maxIter){return 5;}
int64_t w = maxWait >> 1;
for (size_t i = maxIter; i > currIter; --i){
w >>= 1;
if (w < 2){w = 2;}
}
DONTEVEN_MSG("Waiting %" PRId64 " ms out of %" PRId64 " for iteration %zu/%zu", w, maxWait, currIter, maxIter);
return w;
}
/// 64-bits version of ftell /// 64-bits version of ftell
uint64_t ftell(FILE *stream){ uint64_t ftell(FILE *stream){
/// \TODO Windows implementation (e.g. _ftelli64 ?) /// \TODO Windows implementation (e.g. _ftelli64 ?)

2
lib/util.h
View file

@ -14,6 +14,8 @@ namespace Util{
bool stringScan(const std::string &src, const std::string &pattern, std::deque<std::string> &result); bool stringScan(const std::string &src, const std::string &pattern, std::deque<std::string> &result);
void stringToLower(std::string &val); void stringToLower(std::string &val);
int64_t expBackoffMs(const size_t currIter, const size_t maxIter, const int64_t maxWait);
uint64_t ftell(FILE *stream); uint64_t ftell(FILE *stream);
uint64_t fseek(FILE *stream, uint64_t offset, int whence); uint64_t fseek(FILE *stream, uint64_t offset, int whence);