now we use inter-process locking

src/runtime/c/pgf/db.cxx

@@ -7,6 +7,7 @@
 #include <pthread.h>
 
 #include "data.h"
+#include "ipc.h"
 
 PGF_INTERNAL __thread unsigned char* current_base __attribute__((tls_model("initial-exec"))) = NULL;
 PGF_INTERNAL __thread PgfDB* current_db __attribute__((tls_model("initial-exec"))) = NULL;
@@ -344,12 +345,12 @@ PgfDB::PgfDB(const char* filepath, int flags, int mode) {
         throw pgf_systemerror(code, filepath);
     }
 
-    int res = pthread_rwlock_init(&rwlock, NULL);
-    if (res != 0) {
+    try {
+        rwlock = ipc_new_file_rwlock(this->filepath);
+    } catch (pgf_systemerror e) {
         ::free((void *) this->filepath);
-        int code = errno;
         close(fd);
-        throw pgf_systemerror(code);
+        throw e;
     }
 
     if (is_new) {
@@ -389,7 +390,7 @@ PgfDB::~PgfDB() {
     if (fd >= 0)
         close(fd);
 
-    pthread_rwlock_destroy(&rwlock);
+    ipc_release_file_rwlock(filepath, rwlock);
 
     ::free((void*) filepath);
 }
@@ -1108,8 +1109,8 @@ void PgfDB::sync()
 DB_scope::DB_scope(PgfDB *db, DB_scope_mode m)
 {
     int res =
-        (m == READER_SCOPE) ? pthread_rwlock_rdlock(&db->rwlock)
-                            : pthread_rwlock_wrlock(&db->rwlock);
+        (m == READER_SCOPE) ? pthread_rwlock_rdlock(db->rwlock)
+                            : pthread_rwlock_wrlock(db->rwlock);
     if (res != 0)
         throw pgf_systemerror(res);
 
@@ -1125,9 +1126,7 @@ DB_scope::~DB_scope()
 {
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wterminate"
-    int res = pthread_rwlock_unlock(&current_db->rwlock);
-    if (res != 0)
-        throw pgf_systemerror(res);
+    pthread_rwlock_unlock(current_db->rwlock);
 
     current_db    = save_db;
     current_base  = current_db ? (unsigned char*) current_db->ms

src/runtime/c/pgf/db.h

@@ -60,7 +60,7 @@ private:
     const char *filepath;
     malloc_state* ms;
 
-    pthread_rwlock_t rwlock;
+    pthread_rwlock_t *rwlock;
 
     friend class PgfReader;
 

src/runtime/c/pgf/ipc.cxx

@@ -59,6 +59,15 @@ static file_locks *locks = NULL;
 PGF_INTERNAL
 pthread_rwlock_t *ipc_new_file_rwlock(const char* file_path)
 {
+    if (file_path == NULL) {
+        pthread_rwlock_t *rwlock = (pthread_rwlock_t *)
+            malloc(sizeof(pthread_rwlock_t));
+        if (pthread_rwlock_init(rwlock, NULL) != 0) {
+            ipc_error();
+        }
+        return rwlock;
+    }
+
     int pagesize  = getpagesize();
 
     if (locks == NULL) {
@@ -161,21 +170,54 @@ pthread_rwlock_t *ipc_new_file_rwlock(const char* file_path)
         entry->next  = locks->lock_entries;
         locks->lock_entries = offs(entry);
     } else {
-        process_entry *pentry;
-        if (locks->free_process_entries) {
-            pentry = ptr(locks->free_process_entries,process_entry);
-            locks->free_process_entries = pentry->next;
-        } else {
-            if (locks->top+sizeof(process_entry) > pagesize) {
-                pthread_mutex_unlock(&locks->mutex);
-                ipc_toomany();
+        process_entry *pentry = &entry->p;
+        ptr_t(process_entry) *plast = NULL;
+        while (pentry != NULL) {
+            char proc_file[32];
+            sprintf(proc_file, "/proc/%d", pentry->pid);
+            if (access(proc_file, F_OK) != 0) {
+                // if there are dead processes -> remove them
+                if (plast == NULL) {
+                    if (entry->p.next == 0) {
+                        entry->p.pid = 0;
+                        break;
+                    } else {
+                        process_entry *tmp =
+                            ptr(pentry->next, process_entry);
+                        *pentry = *tmp;
+                        tmp->pid  = 0;
+                        tmp->next = locks->free_process_entries;
+                        locks->free_process_entries = offs(tmp);
+                    }
+                } else {
+                    *plast = pentry->next;
+                    pentry->pid  = 0;
+                    pentry->next = locks->free_process_entries;
+                    locks->free_process_entries = offs(pentry);
+                    pentry = ptr(*plast,process_entry);
+                }
+            } else {
+                plast  = &pentry->next;
+                pentry = ptr(*plast,process_entry);
             }
-            pentry = ptr(locks->top,process_entry);
-            locks->top += sizeof(process_entry);
         }
-        pentry->next  = entry->p.next;
-        pentry->pid   = getpid();
-        entry->p.next = offs(pentry);
+
+        if (plast != NULL) {
+            if (locks->free_process_entries) {
+                pentry = ptr(locks->free_process_entries,process_entry);
+                locks->free_process_entries = pentry->next;
+            } else {
+                if (locks->top+sizeof(process_entry) > pagesize) {
+                    pthread_mutex_unlock(&locks->mutex);
+                    ipc_toomany();
+                }
+                pentry = ptr(locks->top,process_entry);
+                locks->top += sizeof(process_entry);
+            }
+            *plast        = offs(pentry);
+        }
+        pentry->pid  = getpid();
+        pentry->next = 0;
     }
 
     pthread_mutex_unlock(&locks->mutex);
@@ -184,8 +226,15 @@ pthread_rwlock_t *ipc_new_file_rwlock(const char* file_path)
 }
 
 PGF_INTERNAL
-void ipc_release_file_rwlock(const char* file_path)
+void ipc_release_file_rwlock(const char* file_path,
+                             pthread_rwlock_t *rwlock)
 {
+    if (file_path == NULL) {
+        pthread_rwlock_destroy(rwlock);
+        free(rwlock);
+        return;
+    }
+
     if (locks == NULL)
         return;
 
@@ -228,6 +277,7 @@ free_it:
                         process_entry *tmp =
                             ptr(pentry->next, process_entry);
                         *pentry = *tmp;
+                        tmp->pid  = 0;
                         tmp->next = locks->free_process_entries;
                         locks->free_process_entries = offs(tmp);
                     }

src/runtime/c/pgf/ipc.h

@@ -5,6 +5,7 @@ PGF_INTERNAL_DECL
 pthread_rwlock_t *ipc_new_file_rwlock(const char* file_path);
 
 PGF_INTERNAL
-void ipc_release_file_rwlock(const char* file_path);
+void ipc_release_file_rwlock(const char* file_path,
+                             pthread_rwlock_t *rwlock);
 
 #endif