add interface for timedwait on semaphores

According to SDL documentation, the SDL implementation of timedwait may
suck on some platforms, so it should only be used, where high CPU usage
during the wait is no issue.

getpckserver() will now only wait for one second for access to the
package server list and return an error instead of waiting indefinitely.

source/src/Makefile

@@ -115,7 +115,7 @@ SERVER_INCLUDES= -DSTANDALONE $(INCLUDES) -I../include
 SERVER_LIBS= -L../lib -lzdll -lenet -lws2_32 -lwinmm
 else
 SERVER_INCLUDES= -DSTANDALONE $(INCLUDES)
-SERVER_LIBS= -L../enet/.libs -lenet -lz -lpthread
+SERVER_LIBS= -L../enet/.libs -lenet -lz -lpthread -lrt
 endif
 
 SERVER_OBJS= \

source/src/autodownload.cpp

@@ -53,13 +53,16 @@ COMMAND(addpckserver, "ss");
 
 void getpckserver() // return a table of all package servers with four columns
 {
-    sem_pckservers.wait();
     vector<char> res;
-    loopv(pckservers) cvecprintf(res, "\"%s\" %d %d %d\n", pckservers[i]->host, pckservers[i]->priority, pckservers[i]->ping, pckservers[i]->resolved);
+    if(sem_pckservers.timedwait(1000)) cvecprintf(res, "\"serverlist is busy, try again later\" "); // single-word return value signals an error
+    else
+    {
+        loopv(pckservers) cvecprintf(res, "\"%s\" %d %d %d\n", pckservers[i]->host, pckservers[i]->priority, pckservers[i]->ping, pckservers[i]->resolved);
+        sem_pckservers.post();
+    }
     if(res.length()) res.last() = '\0';
     else res.add('\0');
     result(res.getbuf());
-    sem_pckservers.post();
 }
 COMMAND(getpckserver, "");
 
@@ -430,7 +433,7 @@ int downloadpackages(bool loadscr) // get all pending packages
     httpget h;
     canceldownloads = false;
     progress_of = loadscr ? pendingpackages.length() : -1;
-    if(sem_pckservers.trywait())
+    if(sem_pckservers.timedwait(1000))
     { // can't lock the server list -> this means, the server ping threads have not finished yet
         if(pendingpackages.length()) conoutf("\f3failed to download packages: still pinging the servers...");
         return 0;

source/src/tools.cpp

@@ -543,6 +543,11 @@ int sl_semaphore::trywait()
     return SDL_SemTryWait((SDL_sem *) data);
 }
 
+int sl_semaphore::timedwait(int howlongmillis)
+{
+    return SDL_SemWaitTimeout((SDL_sem *) data, howlongmillis);
+}
+
 int sl_semaphore::getvalue()
 {
     return SDL_SemValue((SDL_sem *) data);
@@ -579,6 +584,20 @@ int sl_semaphore::trywait()
     return sem_trywait((sem_t *) data);
 }
 
+int sl_semaphore::timedwait(int howlongmillis)
+{
+    struct timespec t;
+    if(clock_gettime(CLOCK_REALTIME, &t))
+    {
+        (*errorcount)++;
+        return sem_trywait((sem_t *) data);
+    }
+    howlongmillis += t.tv_nsec / 1000000;
+    t.tv_nsec = (howlongmillis % 1000) * 1000000;
+    t.tv_sec += howlongmillis / 1000;
+    return sem_timedwait((sem_t *) data, &t);
+}
+
 int sl_semaphore::getvalue()
 {
     int ret;

source/src/tools.h

@@ -1004,6 +1004,7 @@ struct sl_semaphore
     ~sl_semaphore();
     void wait();     // blocks, until semaphore gets available
     int trywait();   // returns 0, if semaphore was locked (like wait(), but returns !=0 instead of blocking)
+    int timedwait(int howlongmillis); // like trywait(), but waits for a litte before returning failure
     int getvalue();  // returns current semaphore value
     void post();     // increments (unlocks) semaphore
 };