per-process file locks on linux (stored in /tmp/DFHack/PID/)

minor signed/unsigned fix

library/DFMemInfo.cpp

@@ -95,7 +95,7 @@ memory_info::memory_info(const memory_info &old)
     d->strings = old.d->strings;
     d->base = old.d->base;
     //d->classes = old.d->classes;
-    for(int i = 0; i < old.d->classes.size(); i++)
+    for(uint32_t i = 0; i < old.d->classes.size(); i++)
     {
         t_class * copy = new t_class(*old.d->classes[i]);
         d->classes.push_back(copy);

library/DFMemInfo.h

@@ -68,7 +68,7 @@ namespace DFHack
         }
         ~t_class()
         {
-            for(int i = 0; i < subs.size();i++)
+            for(uint32_t i = 0; i < subs.size();i++)
             {
                 delete subs[i];
             }

library/DFProcess-linux-SHM.cpp

@@ -52,6 +52,8 @@ class SHMProcess::Private
         suspended = false;
         identified = false;
         useYield = false;
+        my_SVfileLock = -1;
+        my_CLfileLock = -1;
     };
     ~Private(){};
     memory_info * my_descriptor;
@@ -60,6 +62,8 @@ class SHMProcess::Private
     char *my_shm;
     int my_shmid;
     Process* q;
+    int my_SVfileLock;
+    int my_CLfileLock;
     
     bool attached;
     bool suspended;
@@ -70,6 +74,9 @@ class SHMProcess::Private
     
     bool Aux_Core_Attach(bool & versionOK, pid_t & PID);
     bool waitWhile (uint32_t state);
+    bool GetLocks();
+    bool AreLocksOk();
+    void FreeLocks();
 };
 
 // some helpful macros to keep the code bloat in check
@@ -95,6 +102,7 @@ bool SHMProcess::Private::waitWhile (uint32_t state)
         if(cnt == 10000)// check if the other process is still there
         {
             
+            /*
             shmctl(my_shmid, IPC_STAT, &descriptor);
             if(descriptor.shm_nattch == 1)// DF crashed or exited - no way to tell?
             {
@@ -112,6 +120,24 @@ bool SHMProcess::Private::waitWhile (uint32_t state)
             {
                 cnt = 0;
             }
+            */
+            if(!AreLocksOk())
+            {
+                //detach the shared memory
+                shmdt(my_shm);
+                attached = suspended = false;
+                
+                // we aren't the current process anymore
+                g_pProcess = NULL;
+                FreeLocks();
+                
+                throw Error::SHMServerDisappeared();
+                return false;
+            }
+            else
+            {
+                cnt = 0;
+            }
         }
         if(useYield)
         {
@@ -166,6 +192,72 @@ bool SHMProcess::Private::Aux_Core_Attach(bool & versionOK, pid_t & PID)
     return true;
 }
 
+bool SHMProcess::Private::AreLocksOk()
+{
+    // both locks are inited (we hold our lock)
+    if(my_CLfileLock != -1 && my_SVfileLock != -1) 
+    {
+        if(lockf(my_SVfileLock,F_TEST,0) == -1) // and server holds its lock
+        {
+            return true; // OK, locks are good
+        }
+    }
+    // locks are bad
+    return false;
+}
+
+void SHMProcess::Private::FreeLocks()
+{
+    if(my_CLfileLock != -1)
+    {
+        lockf(my_CLfileLock,F_ULOCK,0);
+        close(my_CLfileLock);
+        my_CLfileLock = -1;
+    }
+    if(my_SVfileLock != -1)
+    {
+        close(my_SVfileLock);
+        my_SVfileLock = -1;
+    }
+}
+
+bool SHMProcess::Private::GetLocks()
+{
+    char name[256];
+    // try to acquire locks
+    // look at the server lock, if it's locked, the server is present
+    sprintf(name, "/tmp/DFHack/%d/SVlock",my_pid,name);
+    my_SVfileLock = open(name,O_WRONLY);
+    if(my_SVfileLock == -1)
+    {
+        return false;
+    }
+    
+    if(lockf( my_SVfileLock, F_TEST, 0 ) != -1)
+    {
+        close(my_SVfileLock);
+        return false;
+    }
+    
+    // open the client lock, try to lock it
+    sprintf(name, "/tmp/DFHack/%d/CLlock",my_pid,name);
+    my_CLfileLock = open(name,O_WRONLY);
+    if(my_CLfileLock == -1)
+    {
+        close(my_SVfileLock);
+        return false;
+    }
+    if(lockf(my_CLfileLock,F_TLOCK, 0) == -1)
+    {
+        // couldn't acquire lock
+        close(my_SVfileLock);
+        close(my_CLfileLock);
+        return false;
+    }
+    // ok, we have all the locks!
+    return true;
+}
+
 SHMProcess::SHMProcess(uint32_t PID, vector< memory_info* >& known_versions)
 : d(new Private())
 {
@@ -189,15 +281,12 @@ SHMProcess::SHMProcess(uint32_t PID, vector< memory_info* >& known_versions)
         return;
     }
     
-    /*
-     * Check if there are two processes connected to the segment
-     */
-    shmid_ds descriptor;
-    shmctl(d->my_shmid, IPC_STAT, &descriptor); 
-    if(descriptor.shm_nattch != 2)// badness
+    // set pid and gets lock for it
+    d->my_pid = PID;
+    if(!d->GetLocks())
     {
-        fprintf(stderr,"dfhack: %d : invalid no. of processes connected\n", (int) descriptor.shm_nattch);
-        fprintf(stderr,"detach: %d",shmdt(d->my_shm));
+        fprintf(stderr,"Couldn't get locks for PID %d'\n", PID);
+        shmdt(d->my_shm);
         return;
     }
    
@@ -209,12 +298,16 @@ SHMProcess::SHMProcess(uint32_t PID, vector< memory_info* >& known_versions)
     {
         fprintf(stderr,"DF terminated during reading\n");
         shmdt(d->my_shm);
+        // free locks
+        d->FreeLocks();
         return;
     }
     if(!bridgeOK)
     {
         fprintf(stderr,"SHM bridge version mismatch\n");
         shmdt(d->my_shm);
+        // free locks
+        d->FreeLocks();
         return;
     }
     
@@ -225,6 +318,8 @@ SHMProcess::SHMProcess(uint32_t PID, vector< memory_info* >& known_versions)
     {
         perror("readlink");
         shmdt(d->my_shm);
+        // free locks
+        d->FreeLocks();
         return;
     }
     
@@ -240,6 +335,9 @@ SHMProcess::SHMProcess(uint32_t PID, vector< memory_info* >& known_versions)
     // at this point, DF is stopped and waiting for commands. make it run again
     D_SHMCMD = CORE_RUNNING;
     shmdt(d->my_shm); // detach so we don't attach twice when attach() is called
+    
+    // free locks
+    d->FreeLocks();
 }
 
 bool SHMProcess::isSuspended()
@@ -410,9 +508,16 @@ bool SHMProcess::attach()
     int status;
     if(g_pProcess != 0)
     {
-        cerr << "there's already a different process attached" << endl;
+        // FIXME: throw exception here - programmer error
+        cerr << "client is already attached to a process!" << endl;
         return false;
     }
+    if(!d->GetLocks())
+    {
+        cerr << "server is full or not really there!" << endl;
+        return false;
+    }
+
     /*
     * Attach the segment
     */
@@ -427,10 +532,12 @@ bool SHMProcess::attach()
         }
         d->attached = false;
         cerr << "unable to suspend" << endl;
-        // FIXME: detach sehment here
+        shmdt(d->my_shm);
+        d->FreeLocks();
         return false;
     }
     cerr << "unable to attach" << endl;
+    d->FreeLocks();
     return false;
 }
 
@@ -451,9 +558,11 @@ bool SHMProcess::detach()
         d->suspended = false;
         d->my_shm = 0;
         g_pProcess = 0;
+        d->FreeLocks();
         return true;
     }
     // fail if we can't detach
+    // FIXME: throw exception here??
     perror("failed to detach shared segment");
     return false;
 }

shmserver/shms-linux.cpp

@@ -33,6 +33,8 @@ distribution.
 #include <sys/shm.h>
 #include <sys/types.h>
 #include <sys/ipc.h>
+#include <sys/stat.h>
+#include <fcntl.h>
 #include <unistd.h>
 #include <vector>
 #include <string>
@@ -49,10 +51,14 @@ char *shm = 0;
 int shmid = 0;
 bool inited = 0;
 
+int fd_svlock = 0;
+int fd_cllock = 0;
+
+
 /*******************************************************************************
 *                           SHM part starts here                               *
 *******************************************************************************/
-
+/*
 // FIXME: add error checking?
 bool isValidSHM()
 {
@@ -61,6 +67,25 @@ bool isValidSHM()
     //fprintf(stderr,"ID %d, attached: %d\n",shmid, descriptor.shm_nattch);
     return (descriptor.shm_nattch == 2);
 }
+*/
+
+// is the other side still there?
+bool isValidSHM()
+{
+    // try if CL lock file is free
+    int result = lockf(fd_cllock,F_TEST,0);
+    /*
+    F_TEST: Test the lock:
+    return 0 if the specified section is unlocked or locked by this process;
+    return -1, set errno to EAGAIN (EACCES on some other systems), if another process holds a lock.
+    */
+    
+    // if nobody holds the lock, the SHM isn't valid. file locks are unlocked when the owner closes or crashes.
+    if(result == 0) return false;
+    
+    return true;
+}
+
 uint32_t OS_getPID()
 {
     return getpid();
@@ -84,6 +109,23 @@ void SHM_Init ( void )
         return;
     }
     inited = true;
+    char name[256];
+    char name2[256];
+    
+    // make folder structure for our lock files
+    sprintf(name, "/tmp/DFHack/%d",OS_getPID());
+    mode_t createmode = S_IRWXU | S_IRWXG | S_IROTH | S_IXOTH;
+    mkdir("/tmp/DFHack", createmode);
+    mkdir(name, createmode);
+    
+    // create and lock the server lock file
+    sprintf(name2, "%s/SVlock",name);
+    fd_svlock = open(name2,O_WRONLY | O_CREAT, createmode);
+    lockf( fd_svlock, F_LOCK, 0 );
+    
+    // create the client lock file
+    sprintf(name2, "%s/CLlock",name);
+    fd_cllock = open(name2,O_WRONLY | O_CREAT, createmode);
     
     // name for the segment, an accident waiting to happen
     key_t key = SHM_KEY + OS_getPID();
@@ -134,6 +176,14 @@ void SHM_Destroy ( void )
             shmctl(shmid, IPC_STAT, &descriptor);
         }
         shmctl(shmid,IPC_RMID,NULL);
+        
+        // unlock and close server lock, close client lock
+        lockf(fd_svlock,F_ULOCK,0);
+        close(fd_svlock);
+        close(fd_cllock);
+        fd_svlock = 0;
+        fd_cllock = 0;
+        
         fprintf(stderr,"dfhack: destroyed shared segment.\n");
         inited = false;
     }