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Remove isc_atomic usage from rwlock.c and stats.c

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This commit is contained in:
Ondřej Surý
2018-08-14 11:42:06 +02:00
parent e119de4169
commit e9e55cbd03
4 changed files with 23 additions and 759 deletions
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337
lib/isc/rwlock.c
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@@ -41,10 +41,8 @@
#define RWLOCK_MAX_ADAPTIVE_COUNT 100
#endif
#if defined(ISC_RWLOCK_USEATOMIC)
static isc_result_t
isc__rwlock_lock(isc_rwlock_t *rwl, isc_rwlocktype_t type);
#endif
#ifdef ISC_RWLOCK_TRACE
#include <stdio.h> /* Required for fprintf/stderr. */
@@ -52,7 +50,6 @@ isc__rwlock_lock(isc_rwlock_t *rwl, isc_rwlocktype_t type);
static void
print_lock(const char *operation, isc_rwlock_t *rwl, isc_rwlocktype_t type) {
#if defined(ISC_RWLOCK_USEATOMIC)
fprintf(stderr,
isc_msgcat_get(isc_msgcat, ISC_MSGSET_RWLOCK,
ISC_MSG_PRINTLOCK2,
@@ -69,26 +66,6 @@ print_lock(const char *operation, isc_rwlock_t *rwl, isc_rwlocktype_t type) {
rwl->write_requests, rwl->write_completions,
rwl->cnt_and_flag, rwl->readers_waiting,
rwl->write_granted, rwl->write_quota);
#else
fprintf(stderr,
isc_msgcat_get(isc_msgcat, ISC_MSGSET_RWLOCK,
ISC_MSG_PRINTLOCK,
"rwlock %p thread %lu %s(%s): %s, %u active, "
"%u granted, %u rwaiting, %u wwaiting\n"),
rwl, isc_thread_self(), operation,
(type == isc_rwlocktype_read ?
isc_msgcat_get(isc_msgcat, ISC_MSGSET_RWLOCK,
ISC_MSG_READ, "read") :
isc_msgcat_get(isc_msgcat, ISC_MSGSET_RWLOCK,
ISC_MSG_WRITE, "write")),
(rwl->type == isc_rwlocktype_read ?
isc_msgcat_get(isc_msgcat, ISC_MSGSET_RWLOCK,
ISC_MSG_READING, "reading") :
isc_msgcat_get(isc_msgcat, ISC_MSGSET_RWLOCK,
ISC_MSG_WRITING, "writing")),
rwl->active, rwl->granted,
rwl->readers_waiting, rwl->writers_waiting);
#endif
}
#endif /* ISC_RWLOCK_TRACE */
@@ -107,7 +84,6 @@ isc_rwlock_init(isc_rwlock_t *rwl, unsigned int read_quota,
rwl->magic = 0;
rwl->spins = 0;
#if defined(ISC_RWLOCK_USEATOMIC)
rwl->write_requests = 0;
rwl->write_completions = 0;
rwl->cnt_and_flag = 0;
@@ -120,20 +96,6 @@ isc_rwlock_init(isc_rwlock_t *rwl, unsigned int read_quota,
if (write_quota == 0)
write_quota = RWLOCK_DEFAULT_WRITE_QUOTA;
rwl->write_quota = write_quota;
#else
rwl->type = isc_rwlocktype_read;
rwl->original = isc_rwlocktype_none;
rwl->active = 0;
rwl->granted = 0;
rwl->readers_waiting = 0;
rwl->writers_waiting = 0;
if (read_quota == 0)
read_quota = RWLOCK_DEFAULT_READ_QUOTA;
rwl->read_quota = read_quota;
if (write_quota == 0)
write_quota = RWLOCK_DEFAULT_WRITE_QUOTA;
rwl->write_quota = write_quota;
#endif
result = isc_mutex_init(&rwl->lock);
if (result != ISC_R_SUCCESS)
@@ -176,16 +138,8 @@ void
isc_rwlock_destroy(isc_rwlock_t *rwl) {
REQUIRE(VALID_RWLOCK(rwl));
#if defined(ISC_RWLOCK_USEATOMIC)
REQUIRE(rwl->write_requests == rwl->write_completions &&
rwl->cnt_and_flag == 0 && rwl->readers_waiting == 0);
#else
LOCK(&rwl->lock);
REQUIRE(rwl->active == 0 &&
rwl->readers_waiting == 0 &&
rwl->writers_waiting == 0);
UNLOCK(&rwl->lock);
#endif
rwl->magic = 0;
(void)isc_condition_destroy(&rwl->readable);
@@ -193,8 +147,6 @@ isc_rwlock_destroy(isc_rwlock_t *rwl) {
DESTROYLOCK(&rwl->lock);
}
#if defined(ISC_RWLOCK_USEATOMIC)
/*
* When some architecture-dependent atomic operations are available,
* rwlock can be more efficient than the generic algorithm defined below.
@@ -283,13 +235,9 @@ isc__rwlock_lock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
UNLOCK(&rwl->lock);
}
#if defined(ISC_RWLOCK_USESTDATOMIC)
cntflag = atomic_fetch_add_explicit(&rwl->cnt_and_flag,
READER_INCR,
memory_order_relaxed);
#else
cntflag = isc_atomic_xadd(&rwl->cnt_and_flag, READER_INCR);
#endif
POST(cntflag);
while (1) {
if ((rwl->cnt_and_flag & WRITER_ACTIVE) == 0)
@@ -339,12 +287,8 @@ isc__rwlock_lock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
int32_t prev_writer;
/* enter the waiting queue, and wait for our turn */
#if defined(ISC_RWLOCK_USESTDATOMIC)
prev_writer = atomic_fetch_add_explicit(&rwl->write_requests, 1,
memory_order_relaxed);
#else
prev_writer = isc_atomic_xadd(&rwl->write_requests, 1);
#endif
while (rwl->write_completions != prev_writer) {
LOCK(&rwl->lock);
if (rwl->write_completions != prev_writer) {
@@ -357,16 +301,10 @@ isc__rwlock_lock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
}
while (1) {
#if defined(ISC_RWLOCK_USESTDATOMIC)
int_fast32_t cntflag2 = 0;
atomic_compare_exchange_strong_explicit
(&rwl->cnt_and_flag, &cntflag2, WRITER_ACTIVE,
memory_order_relaxed, memory_order_relaxed);
#else
int32_t cntflag2;
cntflag2 = isc_atomic_cmpxchg(&rwl->cnt_and_flag, 0,
WRITER_ACTIVE);
#endif
if (cntflag2 == 0)
break;
@@ -431,26 +369,17 @@ isc_rwlock_trylock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
return (ISC_R_LOCKBUSY);
/* Otherwise, be ready for reading. */
#if defined(ISC_RWLOCK_USESTDATOMIC)
cntflag = atomic_fetch_add_explicit(&rwl->cnt_and_flag,
READER_INCR,
memory_order_relaxed);
#else
cntflag = isc_atomic_xadd(&rwl->cnt_and_flag, READER_INCR);
#endif
if ((cntflag & WRITER_ACTIVE) != 0) {
/*
* A writer is working. We lose, and cancel the read
* request.
*/
#if defined(ISC_RWLOCK_USESTDATOMIC)
cntflag = atomic_fetch_sub_explicit
(&rwl->cnt_and_flag, READER_INCR,
memory_order_relaxed);
#else
cntflag = isc_atomic_xadd(&rwl->cnt_and_flag,
-READER_INCR);
#endif
/*
* If no other readers are waiting and we've suspended
* new writers in this short period, wake them up.
@@ -466,29 +395,18 @@ isc_rwlock_trylock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
}
} else {
/* Try locking without entering the waiting queue. */
#if defined(ISC_RWLOCK_USESTDATOMIC)
int_fast32_t zero = 0;
if (!atomic_compare_exchange_strong_explicit
(&rwl->cnt_and_flag, &zero, WRITER_ACTIVE,
memory_order_relaxed, memory_order_relaxed))
return (ISC_R_LOCKBUSY);
#else
cntflag = isc_atomic_cmpxchg(&rwl->cnt_and_flag, 0,
WRITER_ACTIVE);
if (cntflag != 0)
return (ISC_R_LOCKBUSY);
#endif
/*
* XXXJT: jump into the queue, possibly breaking the writer
* order.
*/
#if defined(ISC_RWLOCK_USESTDATOMIC)
atomic_fetch_sub_explicit(&rwl->write_completions, 1,
memory_order_relaxed);
#else
(void)isc_atomic_xadd(&rwl->write_completions, -1);
#endif
rwl->write_granted++;
}
@@ -505,7 +423,6 @@ isc_result_t
isc_rwlock_tryupgrade(isc_rwlock_t *rwl) {
REQUIRE(VALID_RWLOCK(rwl));
#if defined(ISC_RWLOCK_USESTDATOMIC)
{
int_fast32_t reader_incr = READER_INCR;
@@ -531,30 +448,6 @@ isc_rwlock_tryupgrade(isc_rwlock_t *rwl) {
return (ISC_R_LOCKBUSY);
}
#else
{
int32_t prevcnt;
/* Try to acquire write access. */
prevcnt = isc_atomic_cmpxchg(&rwl->cnt_and_flag,
READER_INCR, WRITER_ACTIVE);
/*
* There must have been no writer, and there must have
* been at least one reader.
*/
INSIST((prevcnt & WRITER_ACTIVE) == 0 &&
(prevcnt & ~WRITER_ACTIVE) != 0);
if (prevcnt == READER_INCR) {
/*
* We are the only reader and have been upgraded.
* Now jump into the head of the writer waiting queue.
*/
(void)isc_atomic_xadd(&rwl->write_completions, -1);
} else
return (ISC_R_LOCKBUSY);
}
#endif
return (ISC_R_SUCCESS);
}
@@ -565,7 +458,6 @@ isc_rwlock_downgrade(isc_rwlock_t *rwl) {
REQUIRE(VALID_RWLOCK(rwl));
#if defined(ISC_RWLOCK_USESTDATOMIC)
{
/* Become an active reader. */
prev_readers = atomic_fetch_add_explicit(&rwl->cnt_and_flag,
@@ -580,18 +472,6 @@ isc_rwlock_downgrade(isc_rwlock_t *rwl) {
atomic_fetch_add_explicit(&rwl->write_completions, 1,
memory_order_relaxed);
}
#else
{
/* Become an active reader. */
prev_readers = isc_atomic_xadd(&rwl->cnt_and_flag, READER_INCR);
/* We must have been a writer. */
INSIST((prev_readers & WRITER_ACTIVE) != 0);
/* Complete write */
(void)isc_atomic_xadd(&rwl->cnt_and_flag, -WRITER_ACTIVE);
(void)isc_atomic_xadd(&rwl->write_completions, 1);
}
#endif
/* Resume other readers */
LOCK(&rwl->lock);
@@ -612,13 +492,9 @@ isc_rwlock_unlock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
#endif
if (type == isc_rwlocktype_read) {
#if defined(ISC_RWLOCK_USESTDATOMIC)
prev_cnt = atomic_fetch_sub_explicit(&rwl->cnt_and_flag,
READER_INCR,
memory_order_relaxed);
#else
prev_cnt = isc_atomic_xadd(&rwl->cnt_and_flag, -READER_INCR);
#endif
/*
* If we're the last reader and any writers are waiting, wake
* them up. We need to wake up all of them to ensure the
@@ -637,15 +513,10 @@ isc_rwlock_unlock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
* Reset the flag, and (implicitly) tell other writers
* we are done.
*/
#if defined(ISC_RWLOCK_USESTDATOMIC)
atomic_fetch_sub_explicit(&rwl->cnt_and_flag, WRITER_ACTIVE,
memory_order_relaxed);
atomic_fetch_add_explicit(&rwl->write_completions, 1,
memory_order_relaxed);
#else
(void)isc_atomic_xadd(&rwl->cnt_and_flag, -WRITER_ACTIVE);
(void)isc_atomic_xadd(&rwl->write_completions, 1);
#endif
if (rwl->write_granted >= rwl->write_quota ||
rwl->write_requests == rwl->write_completions ||
@@ -682,211 +553,3 @@ isc_rwlock_unlock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
return (ISC_R_SUCCESS);
}
#else /* ISC_RWLOCK_USEATOMIC */
static isc_result_t
doit(isc_rwlock_t *rwl, isc_rwlocktype_t type, bool nonblock) {
bool skip = false;
bool done = false;
isc_result_t result = ISC_R_SUCCESS;
REQUIRE(VALID_RWLOCK(rwl));
LOCK(&rwl->lock);
#ifdef ISC_RWLOCK_TRACE
print_lock(isc_msgcat_get(isc_msgcat, ISC_MSGSET_RWLOCK,
ISC_MSG_PRELOCK, "prelock"), rwl, type);
#endif
if (type == isc_rwlocktype_read) {
if (rwl->readers_waiting != 0)
skip = true;
while (!done) {
if (!skip &&
((rwl->active == 0 ||
(rwl->type == isc_rwlocktype_read &&
(rwl->writers_waiting == 0 ||
rwl->granted < rwl->read_quota)))))
{
rwl->type = isc_rwlocktype_read;
rwl->active++;
rwl->granted++;
done = true;
} else if (nonblock) {
result = ISC_R_LOCKBUSY;
done = true;
} else {
skip = false;
rwl->readers_waiting++;
WAIT(&rwl->readable, &rwl->lock);
rwl->readers_waiting--;
}
}
} else {
if (rwl->writers_waiting != 0)
skip = true;
while (!done) {
if (!skip && rwl->active == 0) {
rwl->type = isc_rwlocktype_write;
rwl->active = 1;
rwl->granted++;
done = true;
} else if (nonblock) {
result = ISC_R_LOCKBUSY;
done = true;
} else {
skip = false;
rwl->writers_waiting++;
WAIT(&rwl->writeable, &rwl->lock);
rwl->writers_waiting--;
}
}
}
#ifdef ISC_RWLOCK_TRACE
print_lock(isc_msgcat_get(isc_msgcat, ISC_MSGSET_RWLOCK,
ISC_MSG_POSTLOCK, "postlock"), rwl, type);
#endif
UNLOCK(&rwl->lock);
return (result);
}
isc_result_t
isc_rwlock_lock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
int32_t cnt = 0;
int32_t max_cnt = rwl->spins * 2 + 10;
isc_result_t result = ISC_R_SUCCESS;
if (max_cnt > RWLOCK_MAX_ADAPTIVE_COUNT)
max_cnt = RWLOCK_MAX_ADAPTIVE_COUNT;
do {
if (cnt++ >= max_cnt) {
result = doit(rwl, type, false);
break;
}
#ifdef ISC_PLATFORM_BUSYWAITNOP
ISC_PLATFORM_BUSYWAITNOP;
#endif
} while (doit(rwl, type, true) != ISC_R_SUCCESS);
rwl->spins += (cnt - rwl->spins) / 8;
return (result);
}
isc_result_t
isc_rwlock_trylock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
return (doit(rwl, type, true));
}
isc_result_t
isc_rwlock_tryupgrade(isc_rwlock_t *rwl) {
isc_result_t result = ISC_R_SUCCESS;
REQUIRE(VALID_RWLOCK(rwl));
LOCK(&rwl->lock);
REQUIRE(rwl->type == isc_rwlocktype_read);
REQUIRE(rwl->active != 0);
/* If we are the only reader then succeed. */
if (rwl->active == 1) {
rwl->original = (rwl->original == isc_rwlocktype_none) ?
isc_rwlocktype_read : isc_rwlocktype_none;
rwl->type = isc_rwlocktype_write;
} else
result = ISC_R_LOCKBUSY;
UNLOCK(&rwl->lock);
return (result);
}
void
isc_rwlock_downgrade(isc_rwlock_t *rwl) {
REQUIRE(VALID_RWLOCK(rwl));
LOCK(&rwl->lock);
REQUIRE(rwl->type == isc_rwlocktype_write);
REQUIRE(rwl->active == 1);
rwl->type = isc_rwlocktype_read;
rwl->original = (rwl->original == isc_rwlocktype_none) ?
isc_rwlocktype_write : isc_rwlocktype_none;
/*
* Resume processing any read request that were blocked when
* we upgraded.
*/
if (rwl->original == isc_rwlocktype_none &&
(rwl->writers_waiting == 0 || rwl->granted < rwl->read_quota) &&
rwl->readers_waiting > 0)
BROADCAST(&rwl->readable);
UNLOCK(&rwl->lock);
}
isc_result_t
isc_rwlock_unlock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
REQUIRE(VALID_RWLOCK(rwl));
LOCK(&rwl->lock);
REQUIRE(rwl->type == type);
UNUSED(type);
#ifdef ISC_RWLOCK_TRACE
print_lock(isc_msgcat_get(isc_msgcat, ISC_MSGSET_RWLOCK,
ISC_MSG_PREUNLOCK, "preunlock"), rwl, type);
#endif
INSIST(rwl->active > 0);
rwl->active--;
if (rwl->active == 0) {
if (rwl->original != isc_rwlocktype_none) {
rwl->type = rwl->original;
rwl->original = isc_rwlocktype_none;
}
if (rwl->type == isc_rwlocktype_read) {
rwl->granted = 0;
if (rwl->writers_waiting > 0) {
rwl->type = isc_rwlocktype_write;
SIGNAL(&rwl->writeable);
} else if (rwl->readers_waiting > 0) {
/* Does this case ever happen? */
BROADCAST(&rwl->readable);
}
} else {
if (rwl->readers_waiting > 0) {
if (rwl->writers_waiting > 0 &&
rwl->granted < rwl->write_quota) {
SIGNAL(&rwl->writeable);
} else {
rwl->granted = 0;
rwl->type = isc_rwlocktype_read;
BROADCAST(&rwl->readable);
}
} else if (rwl->writers_waiting > 0) {
rwl->granted = 0;
SIGNAL(&rwl->writeable);
} else {
rwl->granted = 0;
}
}
}
INSIST(rwl->original == isc_rwlocktype_none);
#ifdef ISC_RWLOCK_TRACE
print_lock(isc_msgcat_get(isc_msgcat, ISC_MSGSET_RWLOCK,
ISC_MSG_POSTUNLOCK, "postunlock"),
rwl, type);
#endif
UNLOCK(&rwl->lock);
return (ISC_R_SUCCESS);
}
#endif /* ISC_RWLOCK_USEATOMIC */