Message ID | 1298277820-8817-8-git-send-email-pbonzini@redhat.com |
---|---|
State | New |
Headers | show |
On 2011-02-21 09:43, Paolo Bonzini wrote: > These are already present in the Win32 implementation, add them to > the pthread wrappers as well. > > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> > --- > qemu-thread-posix.c | 27 +++++++++++++++++++++++++-- > qemu-thread-posix.h | 1 + > 2 files changed, 26 insertions(+), 2 deletions(-) > > diff --git a/qemu-thread-posix.c b/qemu-thread-posix.c > index 28b3f80..2176f81 100644 > --- a/qemu-thread-posix.c > +++ b/qemu-thread-posix.c > @@ -16,9 +16,12 @@ > #include <time.h> > #include <signal.h> > #include <stdint.h> > +#include <assert.h> > #include <string.h> > #include "qemu-thread.h" > > +static pthread_t pthread_null; > + > static void error_exit(int err, const char *msg) > { > fprintf(stderr, "qemu: %s: %s\n", msg, strerror(err)); > @@ -28,8 +31,13 @@ static void error_exit(int err, const char *msg) > void qemu_mutex_init(QemuMutex *mutex) > { > int err; > + pthread_mutexattr_t mutexattr; > > - err = pthread_mutex_init(&mutex->lock, NULL); > + mutex->owner = pthread_null; > + pthread_mutexattr_init(&mutexattr); > + pthread_mutexattr_settype(&mutexattr, PTHREAD_MUTEX_ERRORCHECK); > + err = pthread_mutex_init(&mutex->lock, &mutexattr); > + pthread_mutexattr_destroy(&mutexattr); > if (err) > error_exit(err, __func__); > } > @@ -48,13 +56,20 @@ void qemu_mutex_lock(QemuMutex *mutex) > int err; > > err = pthread_mutex_lock(&mutex->lock); > + mutex->owner = pthread_self(); > if (err) > error_exit(err, __func__); > } > > int qemu_mutex_trylock(QemuMutex *mutex) > { > - return pthread_mutex_trylock(&mutex->lock); > + int err; > + err = pthread_mutex_trylock(&mutex->lock); > + if (err == 0) { > + mutex->owner = pthread_self(); > + } > + > + return !!err; > } > > static void timespec_add_ms(struct timespec *ts, uint64_t msecs) > @@ -85,6 +100,11 @@ void qemu_mutex_unlock(QemuMutex *mutex) > { > int err; > > + /* An EDEADLOCK would arrive after we reset the owner. So this > + assert is for ease of debugging (it lets you see what is the > + actual owner. */ Don't get this. Why do you want to avoid the proper error detection of pthread? > + assert(pthread_equal(mutex->owner, pthread_self())); > + mutex->owner = pthread_null; > err = pthread_mutex_unlock(&mutex->lock); > if (err) > error_exit(err, __func__); > @@ -130,7 +150,10 @@ void qemu_cond_wait(QemuCond *cond, QemuMutex *mutex) > { > int err; > > + assert(pthread_equal(mutex->owner, pthread_self())); > + mutex->owner = pthread_null; > err = pthread_cond_wait(&cond->cond, &mutex->lock); > + mutex->owner = pthread_self(); > if (err) > error_exit(err, __func__); > } > diff --git a/qemu-thread-posix.h b/qemu-thread-posix.h > index 7af371c..11978db 100644 > --- a/qemu-thread-posix.h > +++ b/qemu-thread-posix.h > @@ -4,6 +4,7 @@ > > struct QemuMutex { > pthread_mutex_t lock; > + pthread_t owner; > }; > > struct QemuCond { You said that you want to add owner tracking for assertion in cond_signal/broadcast. That's OK. But the assertions in the mutex layer are redundant for PTHREAD_MUTEX_ERRORCHECK - unless I'm missing something now. Jan
On 02/21/2011 10:50 AM, Jan Kiszka wrote: >> > + /* An EDEADLOCK would arrive after we reset the owner. So this >> > + assert is for ease of debugging (it lets you see what is the >> > + actual owner. */ > > Don't get this. Why do you want to avoid the proper error detection of > pthread? Because by the time you get to error_exit mutex->owner has been NULL-ed out already. So it doesn't help to put a breakpoint on error_exit, you cannot find out which thread was the owner. > But the assertions in the mutex layer > are redundant for PTHREAD_MUTEX_ERRORCHECK - unless I'm missing > something now. Yes, but tracking the mutex's owner gives a bit more specific information when an error happens even for mutexes. I removed them from lock/trylock, but for unlock it's already too late when the error happens. Paolo
On 2011-02-21 11:15, Paolo Bonzini wrote: > On 02/21/2011 10:50 AM, Jan Kiszka wrote: >>>> + /* An EDEADLOCK would arrive after we reset the owner. So this >>>> + assert is for ease of debugging (it lets you see what is the >>>> + actual owner. */ >> >> Don't get this. Why do you want to avoid the proper error detection of >> pthread? > > Because by the time you get to error_exit mutex->owner has been NULL-ed > out already. So it doesn't help to put a breakpoint on error_exit, you > cannot find out which thread was the owner. That's easy, "p <my_mutex>" will tell (the structure contains the owner's tid). And for debugging invalid mutex_unlock calls, it's more interesting to track the call path of that thread which incorrectly claimed to hold the lock. Jan
On 02/21/2011 11:22 AM, Jan Kiszka wrote: > That's easy, "p<my_mutex>" will tell (the structure contains the > owner's tid). > > And for debugging invalid mutex_unlock calls, it's more interesting to > track the call path of that thread which incorrectly claimed to hold the > lock. Ok, will remove. Paolo
diff --git a/qemu-thread-posix.c b/qemu-thread-posix.c index 28b3f80..2176f81 100644 --- a/qemu-thread-posix.c +++ b/qemu-thread-posix.c @@ -16,9 +16,12 @@ #include <time.h> #include <signal.h> #include <stdint.h> +#include <assert.h> #include <string.h> #include "qemu-thread.h" +static pthread_t pthread_null; + static void error_exit(int err, const char *msg) { fprintf(stderr, "qemu: %s: %s\n", msg, strerror(err)); @@ -28,8 +31,13 @@ static void error_exit(int err, const char *msg) void qemu_mutex_init(QemuMutex *mutex) { int err; + pthread_mutexattr_t mutexattr; - err = pthread_mutex_init(&mutex->lock, NULL); + mutex->owner = pthread_null; + pthread_mutexattr_init(&mutexattr); + pthread_mutexattr_settype(&mutexattr, PTHREAD_MUTEX_ERRORCHECK); + err = pthread_mutex_init(&mutex->lock, &mutexattr); + pthread_mutexattr_destroy(&mutexattr); if (err) error_exit(err, __func__); } @@ -48,13 +56,20 @@ void qemu_mutex_lock(QemuMutex *mutex) int err; err = pthread_mutex_lock(&mutex->lock); + mutex->owner = pthread_self(); if (err) error_exit(err, __func__); } int qemu_mutex_trylock(QemuMutex *mutex) { - return pthread_mutex_trylock(&mutex->lock); + int err; + err = pthread_mutex_trylock(&mutex->lock); + if (err == 0) { + mutex->owner = pthread_self(); + } + + return !!err; } static void timespec_add_ms(struct timespec *ts, uint64_t msecs) @@ -85,6 +100,11 @@ void qemu_mutex_unlock(QemuMutex *mutex) { int err; + /* An EDEADLOCK would arrive after we reset the owner. So this + assert is for ease of debugging (it lets you see what is the + actual owner. */ + assert(pthread_equal(mutex->owner, pthread_self())); + mutex->owner = pthread_null; err = pthread_mutex_unlock(&mutex->lock); if (err) error_exit(err, __func__); @@ -130,7 +150,10 @@ void qemu_cond_wait(QemuCond *cond, QemuMutex *mutex) { int err; + assert(pthread_equal(mutex->owner, pthread_self())); + mutex->owner = pthread_null; err = pthread_cond_wait(&cond->cond, &mutex->lock); + mutex->owner = pthread_self(); if (err) error_exit(err, __func__); } diff --git a/qemu-thread-posix.h b/qemu-thread-posix.h index 7af371c..11978db 100644 --- a/qemu-thread-posix.h +++ b/qemu-thread-posix.h @@ -4,6 +4,7 @@ struct QemuMutex { pthread_mutex_t lock; + pthread_t owner; }; struct QemuCond {
These are already present in the Win32 implementation, add them to the pthread wrappers as well. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> --- qemu-thread-posix.c | 27 +++++++++++++++++++++++++-- qemu-thread-posix.h | 1 + 2 files changed, 26 insertions(+), 2 deletions(-)