signals get lost in rare cases

When executing the following test program with dynamorio (drrun), signals might get lost.

The test is rather simple: It starts a thread and sends 2 signals to that thread. On receiving a signal, the thread waits 1s. So the 2nd signal should be processed after 1s.

This works fine most of the time and 2 signals are processed, but in rare cases (1,4% for me) only one signal is received.

Note: Could it be relevant that I am using Suse (SLES 11) with an older kernel, libc, ...?

Note: When using a invalid value for vm_size (e.g. 513M), no error is shown but this test doesn't work anymore. I am not sure if this is a related issue.

Coding:

```
#include
#include
#include
#include

using std::cout;
using std::endl;

void* sayGoodMorningAfterFiveSeconds(void*)
{
usleep(5000000);
cout << "good morning from thread" << endl;
return NULL;
}

static const int signalNumber = 37;

void registerSignalHandler(void (*handler)(int, siginfo_t*, void*))
{
struct sigaction action;
action.sa_handler = NULL;
action.sa_sigaction = handler;
sigemptyset(&action.sa_mask);
action.sa_flags = SA_SIGINFO;
sigaction(signalNumber, &action, NULL);
}

unsigned int signalCount = 0;

void handleSignal(int signalNumber, siginfo_t* signalInfo, void* context)
{
cout << "signal " << signalNumber << " received" << endl;
usleep(1000000);
cout << "leaving signal handler after one second" << endl;
++signalCount;
}

int main()
{
registerSignalHandler(handleSignal);

pthread_t thread;

cout << "before thread creation" << endl;

pthread_create(&thread, NULL, sayGoodMorningAfterFiveSeconds, NULL);

//send signal twice to thread, both should be processed
pthread_kill(thread, signalNumber);
pthread_kill(thread, signalNumber);

pthread_join(thread, NULL);

return signalCount != 2;
}
```