fix(Mutex_POSIX): prevent deadlocks when logging inside signal handlers

Fixes #4939.

Author: sofianehamam

Foundation/include/Poco/Mutex_POSIX.h

@@ -22,6 +22,7 @@
 #include "Poco/Exception.h"
 #include <pthread.h>
 #include <errno.h>
+#include <signal.h>
 
 
 namespace Poco {
@@ -40,6 +41,7 @@ class Foundation_API MutexImpl
 
 private:
 	pthread_mutex_t _mutex;
+	sigset_t set, oldset;
 };
 
 
@@ -56,6 +58,8 @@ class Foundation_API FastMutexImpl: public MutexImpl
 //
 inline void MutexImpl::lockImpl()
 {
+	sigfillset(&set);
+	pthread_sigmask(SIG_BLOCK, &set, &oldset);
 	if (pthread_mutex_lock(&_mutex))
 		throw SystemException("cannot lock mutex");
 }
@@ -77,6 +81,7 @@ inline void MutexImpl::unlockImpl()
 {
 	if (pthread_mutex_unlock(&_mutex))
 		throw SystemException("cannot unlock mutex");
+	pthread_sigmask(SIG_SETMASK, &oldset, NULL);
 }