rwlocks

db.h

@@ -85,7 +85,7 @@ class CAddrDb {
   IMPLEMENT_SERIALIZE (({
     int nVersion = 0;
     READWRITE(nVersion);
-    CRITICAL_BLOCK(cs) {
+    SHARED_CRITICAL_BLOCK(cs) {
       if (fWrite) {
         CAddrDb *db = const_cast<CAddrDb*>(this);
         int nOur = ourId.size();
@@ -158,7 +158,7 @@ class CAddrDb {
       return Get_(ip, wait);
   }
   void GetIPs(std::set<CIP>& ips, int max, bool fOnlyIPv4 = true) {
-    CRITICAL_BLOCK(cs)
+    SHARED_CRITICAL_BLOCK(cs)
       GetIPs_(ips, max, fOnlyIPv4);
   }
 };

main.cpp

@@ -3,6 +3,8 @@
 #include "bitcoin.h"
 #include "db.h"
 
+#define NTHREADS 100
+
 using namespace std;
 
 extern "C" {
@@ -17,7 +19,9 @@ extern "C" void* ThreadCrawler(void* data) {
     CIPPort ip;
     int wait = 5;
     if (!db.Get(ip, wait)) {
-      Sleep(wait*1000);
+      wait *= 1000;
+      wait += rand() % (500 * NTHREADS);
+      Sleep(wait);
       continue;
     }
     int ban = 0;
@@ -75,13 +79,13 @@ int main(void) {
   for (vector<CIP>::iterator it = ips.begin(); it != ips.end(); it++) {
     db.Add(CIPPort(*it, 8333));
   }
-  pthread_t thread[NTHREADS];
-  for (int i=0; i<NTHREADS-2; i++) {
+  pthread_t thread[NTHREADS+2];
+  for (int i=0; i<NTHREADS; i++) {
     pthread_create(&thread[i], NULL, ThreadCrawler, NULL);
   }
-  pthread_create(&thread[NTHREADS-2], NULL, ThreadDumper, NULL);
-  pthread_create(&thread[NTHREADS-1], NULL, ThreadDNS, NULL);
-  for (int i=0; i<NTHREADS; i++) {
+  pthread_create(&thread[NTHREADS], NULL, ThreadDumper, NULL);
+  pthread_create(&thread[NTHREADS+1], NULL, ThreadDNS, NULL);
+  for (int i=0; i<NTHREADS+2; i++) {
     void* res;
     pthread_join(thread[i], &res);
   }

util.h

@@ -45,12 +45,18 @@ inline int myclosesocket(SOCKET& hSocket)
 class CCriticalSection
 {
 protected:
-    pthread_mutex_t mutex;
+    pthread_rwlock_t mutex;
 public:
-    explicit CCriticalSection() { pthread_mutex_init(&mutex, NULL); }
-    ~CCriticalSection() { pthread_mutex_destroy(&mutex); }
-    void Enter() { pthread_mutex_lock(&mutex); }
-    void Leave() { pthread_mutex_unlock(&mutex); }
+    explicit CCriticalSection() { pthread_rwlock_init(&mutex, NULL); }
+    ~CCriticalSection() { pthread_rwlock_destroy(&mutex); }
+    void Enter(bool fShared = false) { 
+      if (fShared) {
+        pthread_rwlock_rdlock(&mutex);
+      } else {
+        pthread_rwlock_wrlock(&mutex);
+      }
+    }
+    void Leave() { pthread_rwlock_unlock(&mutex); }
 };
 
 // Automatically leave critical section when leaving block, needed for exception safety
@@ -59,14 +65,17 @@ class CCriticalBlock
 protected:
     CCriticalSection* pcs;
 public:
-    CCriticalBlock(CCriticalSection& cs) : pcs(&cs) { pcs->Enter(); }
+    CCriticalBlock(CCriticalSection& cs, bool fShared = false) : pcs(&cs) { pcs->Enter(fShared); }
     operator bool() const { return true; }
     ~CCriticalBlock() { pcs->Leave(); }
 };
 
 #define CRITICAL_BLOCK(cs)     \
     if (CCriticalBlock criticalblock = CCriticalBlock(cs))
 
+#define SHARED_CRITICAL_BLOCK(cs)     \
+    if (CCriticalBlock criticalblock = CCriticalBlock(cs, true))
+
 template<typename T1> inline uint256 Hash(const T1 pbegin, const T1 pend)
 {
     static unsigned char pblank[1];