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Broadcast SIGPROF, rather than SIGALRM, when doing real time profiling #207

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Broadcast SIGPROF, rather than SIGALRM, when doing real time profiling #207

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787d18e
Broadcast SIGPROF instead of SIGALRM when doing real_time profiling
palpant-dbx Aug 8, 2019
e75699a
Re-enable real_time_threaded test
palpant-dbx Aug 8, 2019
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8 changes: 2 additions & 6 deletions src/vmprof_common.c
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Original file line number Diff line number Diff line change
Expand Up @@ -281,20 +281,16 @@ ssize_t remove_threads(void)

int broadcast_signal_for_threads(void)
{
int done = 1;
size_t i = 0;
pthread_t self = pthread_self();
pthread_t tid;
while (i < thread_count) {
tid = threads[i];
if (pthread_equal(tid, self)) {
done = 0;
} else if (pthread_kill(tid, SIGALRM)) {
if (pthread_kill(tid, SIGPROF)) {
remove_thread(tid, i);
}
i++;
}
return done;
return 0;
}

int is_main_thread(void)
Expand Down
86 changes: 62 additions & 24 deletions src/vmprof_unix.c
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Original file line number Diff line number Diff line change
Expand Up @@ -170,6 +170,19 @@ void vmprof_release_lock(void) {
__sync_lock_release(&spinlock);
}

void sigalrm_handler(int sig_nr, siginfo_t* info, void *ucontext)
{
// SIGNAL ABUSE AHEAD
// On linux, the prof timer will deliver the signal to the thread which triggered the timer,
// because these timers are based on process and system time, and as such, are thread-aware.
// For the real timer, the signal gets delivered to the main thread, seemingly always.
// Consequently if we want to sample multiple threads, we need to forward this signal.
// This sigalrm handler broadcasts SIGPROF to all registered threads to trigger stack sampling.
if (vmprof_get_signal_type() == SIGALRM && is_main_thread()) {
broadcast_signal_for_threads();
}
}

void sigprof_handler(int sig_nr, siginfo_t* info, void *ucontext)
{
int commit;
Expand Down Expand Up @@ -197,20 +210,6 @@ void sigprof_handler(int sig_nr, siginfo_t* info, void *ucontext)
while (__sync_lock_test_and_set(&spinlock, 1)) {
}

#ifdef VMPROF_UNIX
// SIGNAL ABUSE AHEAD
// On linux, the prof timer will deliver the signal to the thread which triggered the timer,
// because these timers are based on process and system time, and as such, are thread-aware.
// For the real timer, the signal gets delivered to the main thread, seemingly always.
// Consequently if we want to sample multiple threads, we need to forward this signal.
if (vmprof_get_signal_type() == SIGALRM) {
if (is_main_thread() && broadcast_signal_for_threads()) {
__sync_lock_release(&spinlock);
return;
}
}
#endif

prevhandler = signal(SIGSEGV, &segfault_handler);
int fault_code = setjmp(restore_point);
if (fault_code == 0) {
Expand Down Expand Up @@ -266,8 +265,9 @@ int install_sigprof_handler(void)
sa.sa_sigaction = sigprof_handler;
sa.sa_flags = SA_RESTART | SA_SIGINFO;
if (sigemptyset(&sa.sa_mask) == -1 ||
sigaction(vmprof_get_signal_type(), &sa, NULL) == -1)
sigaction(SIGPROF, &sa, NULL) == -1)
return -1;

return 0;
}

Expand All @@ -278,14 +278,43 @@ int remove_sigprof_handler(void)
ign_sigint.sa_flags = 0;
sigemptyset(&ign_sigint.sa_mask);

if (sigaction(vmprof_get_signal_type(), &ign_sigint, NULL) < 0) {
if (sigaction(SIGPROF, &ign_sigint, NULL) < 0) {
fprintf(stderr, "Could not remove the signal handler (for profiling)\n");
return -1;
}

return 0;
}

int install_sigalrm_handler(void)
{
struct sigaction sa;
memset(&sa, 0, sizeof(sa));
sa.sa_sigaction = sigalrm_handler;
sa.sa_flags = SA_RESTART | SA_SIGINFO;
if (sigemptyset(&sa.sa_mask) == -1 ||
sigaction(SIGALRM, &sa, NULL) == -1) {
return -1;
}
return 0;
}

int remove_sigalrm_handler(void)
{
struct sigaction ign_sigint, prev;
ign_sigint.sa_handler = SIG_IGN;
ign_sigint.sa_flags = 0;
sigemptyset(&ign_sigint.sa_mask);

if (sigaction(SIGALRM, &ign_sigint, NULL) < 0) {
fprintf(stderr, "Could not remove the signal handler (for profiling)\n");
return -1;
}

return 0;
}

int install_sigprof_timer(void)
int install_timer(void)
{
static struct itimerval timer;
timer.it_interval.tv_sec = 0;
Expand All @@ -296,7 +325,7 @@ int install_sigprof_timer(void)
return 0;
}

int remove_sigprof_timer(void)
int remove_timer(void)
{
static struct itimerval timer;
timerclear(&(timer.it_interval));
Expand All @@ -311,7 +340,7 @@ int remove_sigprof_timer(void)
void atfork_disable_timer(void)
{
if (vmprof_get_profile_interval_usec() > 0) {
remove_sigprof_timer();
remove_timer();
vmprof_set_enabled(0);
}
}
Expand All @@ -326,7 +355,7 @@ void atfork_close_profile_file(void)
void atfork_enable_timer(void)
{
if (vmprof_get_profile_interval_usec() > 0) {
install_sigprof_timer();
install_timer();
vmprof_set_enabled(1);
}
}
Expand Down Expand Up @@ -366,7 +395,14 @@ int vmprof_enable(int memory, int native, int real_time)
goto error;
if (install_sigprof_handler() == -1)
goto error;
if (install_sigprof_timer() == -1)
/* When using real-time profiling, we also register a handler for SIGALRM,
* which will broadcast SIGPROF to all registered threads.
*/
if (real_time) {
if (install_sigalrm_handler() == -1)
goto error;
}
if (install_timer() == -1)
goto error;
signal_handler_ignore = 0;
return 0;
Expand Down Expand Up @@ -398,15 +434,17 @@ int vmprof_disable(void)
disable_cpyprof();
#endif

if (remove_sigprof_timer() == -1) {
if (remove_timer() == -1) {
return -1;
}
if (remove_sigprof_handler() == -1) {
return -1;
}
#ifdef VMPROF_UNIX
if ((vmprof_get_signal_type() == SIGALRM) && remove_threads() == -1) {
return -1;
if (vmprof_get_signal_type() == SIGALRM) {
if (remove_threads() == -1 || remove_sigalrm_handler() == -1) {
return -1;
}
}
#endif
flush_codes();
Expand Down
8 changes: 6 additions & 2 deletions src/vmprof_unix.h
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Expand Up @@ -53,17 +53,21 @@ int get_stack_trace(PY_THREAD_STATE_T * current, void** result, int max_depth, i
void segfault_handler(int arg);
int _vmprof_sample_stack(struct profbuf_s *p, PY_THREAD_STATE_T * tstate, ucontext_t * uc);
void sigprof_handler(int sig_nr, siginfo_t* info, void *ucontext);
void sigalrm_handler(int sig_nr, siginfo_t* info, void *ucontext);


/* *************************************************************
* the setup and teardown functions
* *************************************************************
*/


int install_sigprof_handler(void);
int remove_sigprof_handler(void);
int install_sigprof_timer(void);
int remove_sigprof_timer(void);
int install_sigalrm_handler(void);
int remove_sigalrm_handler(void);
int install_timer(void);
int remove_timer(void);
void atfork_disable_timer(void);
void atfork_enable_timer(void);
void atfork_close_profile_file(void);
Expand Down
1 change: 0 additions & 1 deletion vmprof/test/test_run.py
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Expand Up @@ -255,7 +255,6 @@ def test_vmprof_real_time():
assert d[foo_time_name] > 0


@py.test.mark.xfail()
@py.test.mark.skipif("'__pypy__' in sys.builtin_module_names")
@py.test.mark.skipif("sys.platform == 'win32'")
@py.test.mark.parametrize("insert_foo,remove_bar", [
Expand Down