Use a lock to synchronize writes to symbol table

gc-notes.txt

@@ -12,8 +12,6 @@ TODO:
 
 - multiple mutators, and threading functions/types.  probably want this on a new branch, when ready
   part of this is implementing the beginnings of srfi-18, to create multiple threads, sync them, etc
-  TODO items:
-  - lock writes to symbol table
 
 - need to cooperate when a mutator is blocked
   might be able to stop a thread and do a minor GC on it, but no longjmp until after major GC.

runtime.c

@@ -102,6 +102,7 @@ static symbol_type __EOF = {{0}, eof_tag, "", nil}; // symbol_type in lieu of cu
 const object Cyc_EOF = &__EOF;
 static ck_hs_t symbol_table;
 static int symbol_table_size = 65536;
+static pthread_mutex_t symbol_table_lock;
 
 // Functions to support concurrency kit hashset
 // These are specifically for a table of symbols
@@ -168,6 +169,10 @@ void gc_init_heap(long heap_size)
     fprintf(stderr, "Unable to initialize symbol table\n");
     exit(1);
   }
+  if (pthread_mutex_init(&(symbol_table_lock), NULL) != 0) {
+    fprintf(stderr, "Unable to initialize symbol_table_lock mutex\n");
+    exit(1);
+  }
 }
 
 gc_heap *gc_get_heap()
@@ -245,13 +250,14 @@ object find_symbol_by_name(const char *name) {
 
 object add_symbol(symbol_type *psym) {
   //printf("Adding symbol %s, table size = %ld\n", symbol_pname(psym), ck_hs_count(&symbol_table));
-  // TODO: lock table here, only allow one writer at a time
-  // TODO: grow table if it is not big enough
+  pthread_mutex_lock(&symbol_table_lock); // Only 1 "writer" allowed
   if (ck_hs_count(&symbol_table) == symbol_table_size) {
+    // TODO: grow table if it is not big enough
     fprintf(stderr, "Ran out of symbol table entries\n");
     exit(1);
   }
   set_insert(&symbol_table, psym);
+  pthread_mutex_unlock(&symbol_table_lock);
   return psym;
 }