Fix data races in `os2/env_linux.odin`

Switched to a recursive mutex so that procedures which need to perform
lookups can do so while also maintaining the lock across their entire
body in order to guarantee atomicity for each environment operation.

core/os/os2/env_linux.odin

@@ -20,19 +20,18 @@ NOT_FOUND :: -1
 // the environment is a 0 delimited list of <key>=<value> strings
 _env: [dynamic]string
 
-_env_mutex: sync.Mutex
+_env_mutex: sync.Recursive_Mutex
 
 // We need to be able to figure out if the environment variable
 // is contained in the original environment or not. This also
 // serves as a flag to determine if we have built _env.
-_org_env_begin: uintptr
-_org_env_end:   uintptr
+_org_env_begin: uintptr // atomic
+_org_env_end:   uintptr // guarded by _env_mutex
 
 // Returns value + index location into _env
 // or -1 if not found
 _lookup :: proc(key: string) -> (value: string, idx: int) {
-	sync.mutex_lock(&_env_mutex)
-	defer sync.mutex_unlock(&_env_mutex)
+	sync.guard(&_env_mutex)
 
 	for entry, i in _env {
 		if k, v := _kv_from_entry(entry); k == key {
@@ -43,7 +42,7 @@ _lookup :: proc(key: string) -> (value: string, idx: int) {
 }
 
 _lookup_env :: proc(key: string, allocator: runtime.Allocator) -> (value: string, found: bool) {
-	if _org_env_begin == 0 {
+	if intrinsics.atomic_load_explicit(&_org_env_begin, .Acquire) == 0 {
 		_build_env()
 	}
 
@@ -55,9 +54,10 @@ _lookup_env :: proc(key: string, allocator: runtime.Allocator) -> (value: string
 }
 
 _set_env :: proc(key, v_new: string) -> Error {
-	if _org_env_begin == 0 {
+	if intrinsics.atomic_load_explicit(&_org_env_begin, .Acquire) == 0 {
 		_build_env()
 	}
+	sync.guard(&_env_mutex)
 
 	// all key values are stored as "key=value\x00"
 	kv_size := len(key) + len(v_new) + 2
@@ -65,8 +65,6 @@ _set_env :: proc(key, v_new: string) -> Error {
 		if v_curr == v_new {
 			return nil
 		}
-		sync.mutex_lock(&_env_mutex)
-		defer sync.mutex_unlock(&_env_mutex)
 
 		unordered_remove(&_env, idx)
 
@@ -101,16 +99,15 @@ _set_env :: proc(key, v_new: string) -> Error {
 	intrinsics.mem_copy_non_overlapping(&val_slice[0], raw_data(v_new), len(v_new))
 	val_slice[len(v_new)] = 0
 
-	sync.mutex_lock(&_env_mutex)
 	append(&_env, string(k_addr[:kv_size - 1]))
-	sync.mutex_unlock(&_env_mutex)
 	return nil
 }
 
 _unset_env :: proc(key: string) -> bool {
-	if _org_env_begin == 0 {
+	if intrinsics.atomic_load_explicit(&_org_env_begin, .Acquire) == 0 {
 		_build_env()
 	}
+	sync.guard(&_env_mutex)
 
 	v: string
 	i: int
@@ -118,9 +115,7 @@ _unset_env :: proc(key: string) -> bool {
 		return false
 	}
 
-	sync.mutex_lock(&_env_mutex)
 	unordered_remove(&_env, i)
-	sync.mutex_unlock(&_env_mutex)
 
 	if _is_in_org_env(v) {
 		return true
@@ -134,8 +129,7 @@ _unset_env :: proc(key: string) -> bool {
 }
 
 _clear_env :: proc() {
-	sync.mutex_lock(&_env_mutex)
-	defer sync.mutex_unlock(&_env_mutex)
+	sync.guard(&_env_mutex)
 
 	for kv in _env {
 		if !_is_in_org_env(kv) {
@@ -145,14 +139,16 @@ _clear_env :: proc() {
 	clear(&_env)
 
 	// nothing resides in the original environment either
-	_org_env_begin = ~uintptr(0)
+	intrinsics.atomic_store_explicit(&_org_env_begin, ~uintptr(0), .Release)
 	_org_env_end = ~uintptr(0)
 }
 
 _environ :: proc(allocator: runtime.Allocator) -> (environ: []string, err: Error) {
-	if _org_env_begin == 0 {
+	if intrinsics.atomic_load_explicit(&_org_env_begin, .Acquire) == 0 {
 		_build_env()
 	}
+	sync.guard(&_env_mutex)
+
 	env := make([dynamic]string, 0, len(_env), allocator) or_return
 	defer if err != nil {
 		for e in env {
@@ -161,8 +157,6 @@ _environ :: proc(allocator: runtime.Allocator) -> (environ: []string, err: Error
 		delete(env)
 	}
 
-	sync.mutex_lock(&_env_mutex)
-	defer sync.mutex_unlock(&_env_mutex)
 	for entry in _env {
 		s := clone_string(entry, allocator) or_return
 		append(&env, s)
@@ -174,7 +168,7 @@ _environ :: proc(allocator: runtime.Allocator) -> (environ: []string, err: Error
 // The entire environment is stored as 0 terminated strings,
 // so there is no need to clone/free individual variables
 export_cstring_environment :: proc(allocator: runtime.Allocator) -> []cstring {
-	if _org_env_begin == 0 {
+	if intrinsics.atomic_load_explicit(&_org_env_begin, .Acquire) == 0 {
 		// The environment has not been modified, so we can just
 		// send the original environment
 		org_env := _get_original_env()
@@ -182,12 +176,11 @@ export_cstring_environment :: proc(allocator: runtime.Allocator) -> []cstring {
 		for ; org_env[n] != nil; n += 1 {}
 		return slice.clone(org_env[:n + 1], allocator)
 	}
+	sync.guard(&_env_mutex)
 
 	// NOTE: already terminated by nil pointer via + 1
 	env := make([]cstring, len(_env) + 1, allocator)
 
-	sync.mutex_lock(&_env_mutex)
-	defer sync.mutex_unlock(&_env_mutex)
 	for entry, i in _env {
 		env[i] = cstring(raw_data(entry))
 	}
@@ -195,15 +188,14 @@ export_cstring_environment :: proc(allocator: runtime.Allocator) -> []cstring {
 }
 
 _build_env :: proc() {
-	sync.mutex_lock(&_env_mutex)
-	defer sync.mutex_unlock(&_env_mutex)
-	if _org_env_begin != 0 {
+	sync.guard(&_env_mutex)
+	if intrinsics.atomic_load_explicit(&_org_env_begin, .Acquire) != 0 {
 		return
 	}
 
 	_env = make(type_of(_env), runtime.heap_allocator())
 	cstring_env := _get_original_env()
-	_org_env_begin = uintptr(rawptr(cstring_env[0]))
+	intrinsics.atomic_store_explicit(&_org_env_begin, uintptr(rawptr(cstring_env[0])), .Release)
 	for i := 0; cstring_env[i] != nil; i += 1 {
 		bytes := ([^]u8)(cstring_env[i])
 		n := len(cstring_env[i])
@@ -235,5 +227,5 @@ _kv_addr_from_val :: #force_inline proc(val: string, key: string) -> ([^]u8, [^]
 
 _is_in_org_env :: #force_inline proc(env_data: string) -> bool {
 	addr := uintptr(raw_data(env_data))
-	return addr >= _org_env_begin && addr < _org_env_end
+	return addr >= intrinsics.atomic_load_explicit(&_org_env_begin, .Acquire) && addr < _org_env_end
 }