fix #21360, make global bindings thread safe (#32370)

Author: JeffBezanson

doc/src/devdocs/locks.md

@@ -34,6 +34,10 @@ The following is a leaf lock (level 2), and only acquires level 1 locks (safepoi
 
 >   * typecache
 
+The following is a level 2 lock:
+
+>   * Module->lock
+
 The following is a level 3 lock, which can only acquire level 1 or level 2 locks internally:
 
 >   * Method->writelock
@@ -102,6 +106,8 @@ Type declarations : toplevel lock
 
 Type application : typecache lock
 
+Global variable tables : Module->lock
+
 Module serializer : toplevel lock
 
 JIT & type-inference : codegen lock

src/julia.h

@@ -462,7 +462,7 @@ typedef struct {
     jl_value_t *value;
     jl_value_t *globalref;  // cached GlobalRef for this binding
     struct _jl_module_t *owner;  // for individual imported bindings
-    uint8_t constp:1;
+    uint8_t constp;
     uint8_t exportp:1;
     uint8_t imported:1;
     uint8_t deprecated:2; // 0=not deprecated, 1=renamed, 2=moved to another package
@@ -486,6 +486,7 @@ typedef struct _jl_module_t {
     uint32_t counter;
     int32_t nospecialize;  // global bit flags: initialization for new methods
     uint8_t istopmod;
+    jl_mutex_t lock;
 } jl_module_t;
 
 // one Type-to-Value entry