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Commit c1b544f5 authored by Xavier Thompson's avatar Xavier Thompson
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Fix contention detection with mutex instead of atomic operations

parent f34cecbf
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Showing with 36 additions and 113 deletions
Cython/Utility/CyObjects.cpp
View file @ c1b544f5
......@@ -20,15 +20,6 @@
#define CyObject_NO_OWNER -1
#define CyObject_MANY_OWNERS -2
#define CyObject_WRITER_OFFSET (16)
#define CyObject_FETCH_CONTENDERS_ADD_WRITER(n) n.fetch_add((1 << CyObject_WRITER_OFFSET))
#define CyObject_FETCH_CONTENDERS_SUB_WRITER(n) n.fetch_sub((1 << CyObject_WRITER_OFFSET))
#define CyObject_FETCH_CONTENDERS_ADD_READER(n) n.fetch_add(1)
#define CyObject_FETCH_CONTENDERS_SUB_READER(n) n.fetch_sub(1)
#define CyObject_WRITERS_FROM_CONTENDERS(n) (n >> CyObject_WRITER_OFFSET)
#define CyObject_READERS_FROM_CONTENDERS(n) (n & ((1 << CyObject_WRITER_OFFSET) -1))
#define CyObject_HAS_WRITER_CONTENDERS(n) (n > (1 << CyObject_WRITER_OFFSET) - 1)
#define CyObject_CONTENDING_WRITER_FLAG (1 << 0)
#define CyObject_CONTENDING_READER_FLAG (1 << 1)
......@@ -50,7 +41,6 @@
pthread_cond_t wait_writer_depart;
atomic<pid_t> owner_id;
atomic_int32_t readers_nb;
atomic_uint32_t contenders;
uint32_t write_count;
public:
RecursiveUpgradeableRWLock() {
......@@ -60,7 +50,6 @@
this->owner_id = CyObject_NO_OWNER;
this->readers_nb = 0;
this->write_count = 0;
this->contenders = 0;
}
void wlock();
void rlock();
......@@ -327,8 +316,6 @@
void RecursiveUpgradeableRWLock::rlock() {
pid_t caller_id = syscall(SYS_gettid);
CyObject_FETCH_CONTENDERS_ADD_READER(this->contenders);
if (this->owner_id == caller_id) {
++this->readers_nb;
return;
......@@ -348,25 +335,17 @@ void RecursiveUpgradeableRWLock::rlock() {
int RecursiveUpgradeableRWLock::tryrlock() {
pid_t caller_id = syscall(SYS_gettid);
int contenders = CyObject_FETCH_CONTENDERS_ADD_READER(this->contenders);
if (this->owner_id == caller_id) {
++this->readers_nb;
return 0;
}
if (CyObject_HAS_WRITER_CONTENDERS(contenders)) {
CyObject_FETCH_CONTENDERS_SUB_READER(this->contenders);
return CyObject_CONTENDING_WRITER_FLAG;
}
// we must lock here, because a trylock could fail also when another thread is currently read-locking or read-unlocking
// but this means we might miss a writer arriving and leaving
pthread_mutex_lock(&this->guard);
if (this->write_count > 0) {
pthread_mutex_unlock(&this->guard);
CyObject_FETCH_CONTENDERS_SUB_READER(this->contenders);
return CyObject_CONTENDING_WRITER_FLAG;
}
......@@ -391,15 +370,11 @@ void RecursiveUpgradeableRWLock::unrlock() {
}
pthread_mutex_unlock(&this->guard);
CyObject_FETCH_CONTENDERS_SUB_READER(this->contenders);
}
void RecursiveUpgradeableRWLock::wlock() {
pid_t caller_id = syscall(SYS_gettid);
CyObject_FETCH_CONTENDERS_ADD_WRITER(this->contenders);
if (this->owner_id == caller_id) {
if (this->write_count) {
++this->write_count;
......@@ -442,8 +417,6 @@ void RecursiveUpgradeableRWLock::wlock() {
int RecursiveUpgradeableRWLock::trywlock() {
pid_t caller_id = syscall(SYS_gettid);
uint32_t contenders = CyObject_FETCH_CONTENDERS_ADD_WRITER(this->contenders);
if (this->owner_id == caller_id) {
if (this->write_count) {
++this->write_count;
......@@ -451,35 +424,17 @@ int RecursiveUpgradeableRWLock::trywlock() {
}
}
if (CyObject_HAS_WRITER_CONTENDERS(contenders) > 0) {
CyObject_FETCH_CONTENDERS_SUB_WRITER(this->contenders);
return CyObject_CONTENDING_WRITER_FLAG;
}
if (contenders > 0) {
CyObject_FETCH_CONTENDERS_SUB_WRITER(this->contenders);
return CyObject_CONTENDING_READER_FLAG;
}
if (pthread_mutex_trylock(&this->guard) != 0) {
// another thread is currently doing a lock operation on this lock, but we don't know what it is.
// we could choose to do a blocking lock instead of a trylock here.
// that way we would not detect when an unlock overlaps with this trylock,
// but also all the contending readers and / or writers could leave while we block,
// so we wouldn't detect those contentions either.
return CyObject_CONTENDING_WRITER_FLAG | CyObject_CONTENDING_READER_FLAG;
}
pthread_mutex_lock(&this->guard);
if (this->owner_id != caller_id) {
if (this->readers_nb > 0) {
pthread_mutex_unlock(&this->guard);
CyObject_FETCH_CONTENDERS_SUB_WRITER(this->contenders);
return CyObject_CONTENDING_READER_FLAG;
}
if (this->write_count > 0) {
pthread_mutex_unlock(&this->guard);
CyObject_FETCH_CONTENDERS_SUB_WRITER(this->contenders);
return CyObject_CONTENDING_WRITER_FLAG;
}
......@@ -507,15 +462,12 @@ void RecursiveUpgradeableRWLock::unwlock() {
}
pthread_mutex_unlock(&this->guard);
CyObject_FETCH_CONTENDERS_SUB_WRITER(this->contenders);
}
void LogLock::rlock() {
pid_t caller_id = syscall(SYS_gettid);
int contenders = CyObject_FETCH_CONTENDERS_ADD_READER(this->contenders);
if (this->owner_id == caller_id) {
++this->readers_nb;
return;
......@@ -523,25 +475,15 @@ void LogLock::rlock() {
pthread_mutex_lock(&this->guard);
if (CyObject_HAS_WRITER_CONTENDERS(contenders)) {
if (this->write_count > 0) {
pid_t lock_owner = this->owner_id;
pid_t owner_id = this->owner_id;
printf(
"Contention with a writer detected while rlocking lock [%p] in thread #%d:\n"
" - lock was already wlocked by thread %d\n"
"\n"
,this, caller_id, lock_owner
);
}
else {
printf(
"Contention with a writer detected while rlocking lock [%p] in thread #%d:\n"
" - the writer was already gone by the time we could inspect who owned the thread\n"
"\n"
,this, caller_id
,this, caller_id, owner_id
);
}
}
while (this->write_count > 0) {
pthread_cond_wait(&this->wait_writer_depart, &this->guard);
......@@ -556,8 +498,6 @@ void LogLock::wlock() {
pid_t caller_id = syscall(SYS_gettid);
uint32_t contenders = CyObject_FETCH_CONTENDERS_ADD_WRITER(this->contenders);
if (this->owner_id == caller_id) {
if (this->write_count) {
++this->write_count;
......@@ -567,27 +507,12 @@ void LogLock::wlock() {
pthread_mutex_lock(&this->guard);
if ((CyObject_HAS_WRITER_CONTENDERS(contenders) > 0) && (this->write_count > 0)) {
pid_t lock_owner = this->owner_id;
printf(
"Contention with another writer detected while wlocking lock [%p] in thread #%d:\n"
" - lock owner is thread %d\n"
"\n"
,this, caller_id, lock_owner
);
}
pid_t owner_id = this->owner_id;
else if (CyObject_READERS_FROM_CONTENDERS(contenders) > 0) {
pid_t lock_owner = this->owner_id;
if (lock_owner > 0) {
printf(
"Contention with a reader thread detected while wlocking lock [%p] in thread #%d:\n"
" - reader thread is %d\n"
"\n"
,this, caller_id, lock_owner
);
}
else if (lock_owner == CyObject_MANY_OWNERS) {
if (owner_id != caller_id) {
if (this->readers_nb > 0) {
if (owner_id == CyObject_MANY_OWNERS) {
printf(
"Contention with several other reader threads detected while wlocking lock [%p] in thread #%d:\n"
"\n"
......@@ -596,29 +521,27 @@ void LogLock::wlock() {
}
else {
printf(
"Contention with unidentified readers detected while wlocking lock [%p] in thread #%d:\n"
" - the readers were already gone by the time we could inspect lock ownership\n"
"Contention with a reader thread detected while wlocking lock [%p] in thread #%d:\n"
" - reader thread is %d\n"
"\n"
,this, caller_id
,this, caller_id, owner_id
);
}
}
else if (contenders > 0) {
while (this->readers_nb > 0) {
pthread_cond_wait(&this->wait_readers_depart, &this->guard);
}
if (this->write_count > 0) {
printf(
"Contention with another writer detected while wlocking lock [%p] in thread #%d:\n"
" - the writer was already gone by the time we could inspect who owned the thread\n"
" - lock owner is thread %d\n"
"\n"
,this, caller_id
,this, caller_id, owner_id
);
}
if (this->owner_id != caller_id) {
while (this->readers_nb > 0) {
pthread_cond_wait(&this->wait_readers_depart, &this->guard);
}
while (this->write_count > 0) {
pthread_cond_wait(&this->wait_writer_depart, &this->guard);
}
......
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