Removed usage of pthreads and replaced with std C++ features

- Replaced pthread_mutex_t in modsecurity::operators::Pm with std::mutex
- Replaced pthread's thread usage in reading_logs_via_rule_message
  example with std::thread.
  - Simplified and modernized C++ code.
- Removed unnecessary includes of pthread.h

src/collection/backend/in_memory-per_process.cc

@@ -25,8 +25,6 @@
 #include <memory>
 #endif
 
-#include <pthread.h>
-
 #include "modsecurity/variable_value.h"
 #include "src/utils/regex.h"
 #include "src/utils/string.h"

src/collection/backend/lmdb.cc

@@ -27,8 +27,6 @@
 #include <string>
 #include <memory>
 
-#include <pthread.h>
-
 #include "modsecurity/variable_value.h"
 #include "src/utils/regex.h"
 #include "src/variables/variable.h"

src/collection/backend/lmdb.h

@@ -27,12 +27,10 @@
 
 #ifdef WITH_LMDB
 #include <lmdb.h>
-#include <semaphore.h>
 #endif  // WITH_LMDB
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <fcntl.h>
-#include <pthread.h>
 
 #include "modsecurity/variable_value.h"
 #include "modsecurity/collection/collection.h"

src/operators/pm.cc

@@ -39,9 +39,6 @@ Pm::~Pm() {
 
     free(m_p);
     m_p = NULL;
-#ifdef MODSEC_MUTEX_ON_PM
-    pthread_mutex_destroy(&m_lock);
-#endif
 }
 
 
@@ -89,11 +86,12 @@ bool Pm::evaluate(Transaction *transaction, RuleWithActions *rule,
     pt.ptr = NULL;
     const char *match = NULL;
 #ifdef MODSEC_MUTEX_ON_PM
-    pthread_mutex_lock(&m_lock);
+    {
+    const std::lock_guard lock(m_mutex);
 #endif
     rc = acmp_process_quick(&pt, &match, input.c_str(), input.length());
 #ifdef MODSEC_MUTEX_ON_PM
-    pthread_mutex_unlock(&m_lock);
+    }
 #endif
 
     if (rc >= 0 && transaction) {
@@ -118,9 +116,6 @@ bool Pm::init(const std::string &file, std::string *error) {
     std::istringstream *iss;
     const char *err = NULL;
 
-#ifdef MODSEC_MUTEX_ON_PM
-    pthread_mutex_init(&m_lock, NULL);
-#endif
     char *content = parse_pm_content(m_param.c_str(), m_param.length(), &err);
     if (content == NULL) {
         iss = new std::istringstream(m_param);

src/operators/pm.h

@@ -20,6 +20,7 @@
 #include <list>
 #include <memory>
 #include <utility>
+#include <mutex>
 
 #include "src/operators/operator.h"
 #include "src/utils/acmp.h"
@@ -56,7 +57,7 @@ class Pm : public Operator {
 #ifdef MODSEC_MUTEX_ON_PM
 
  private:
-    pthread_mutex_t m_lock;
+    std::mutex m_mutex;
 #endif
 };