avoid request stalls during proactive rebuilds

src/lib/compiler.cpp

@@ -296,7 +296,7 @@ String compiler_registry_lock_file_name(Request* context)
 	return(compiler_registry_file_name(context) + ".lock");
 }
 
-int compiler_open_lock_file(String file_name, String purpose)
+int compiler_open_lock_file(String file_name, String purpose, bool nonblocking = false)
 {
 	(void)purpose;
 	auto lock_dir = dirname(file_name);
@@ -309,8 +309,13 @@ int compiler_open_lock_file(String file_name, String purpose)
 		return(fdlock);
 	}
 	fcntl(fdlock, F_SETFD, FD_CLOEXEC);
-	if(flock(fdlock, LOCK_EX) != 0)
+	if(flock(fdlock, LOCK_EX | (nonblocking ? LOCK_NB : 0)) != 0)
 	{
+		if(nonblocking && (errno == EWOULDBLOCK || errno == EAGAIN))
+		{
+			close(fdlock);
+			return(-2);
+		}
 		close(fdlock);
 		printf("(!) Could not lock file %s\n", file_name.c_str());
 		return(-1);
@@ -845,7 +850,19 @@ SharedUnit* compiler_get_shared_unit_internal(Request* context, String file_name
 	SharedUnit* su = new SharedUnit();
 	setup_unit_paths(context, su, file_name);
 
-	int fdlock = compiler_open_lock_file(su->wasm_name + ".lock", "shared-unit:" + file_name);
+	int fdlock = compiler_open_lock_file(su->wasm_name + ".lock", "shared-unit:" + file_name, !force_recompile);
+	if(fdlock == -2 && file_exists(su->wasm_name))
+	{
+		auto state = inspect_shared_unit_filesystem(context, su);
+		su->api_declarations = split(file_get_contents(su->api_file_name), "\n");
+		su->last_compiled = state.compiled_time;
+		su->compile_status = "rebuilding";
+		compiler_record_observed_filesystem_state(su, state);
+		context->server->units[file_name] = su;
+		return(su);
+	}
+	if(fdlock == -2)
+		fdlock = compiler_open_lock_file(su->wasm_name + ".lock", "shared-unit:" + file_name);
 	if(fdlock == -1)
 	{
 		su->compiler_messages = "could not open compile lock";
@@ -947,6 +964,17 @@ bool compiler_unit_compile_pending(Request* context, String file_name)
 	return(true);
 }
 
+bool compiler_unit_compile_in_progress(Request* context, String file_name)
+{
+	SharedUnit su;
+	setup_unit_paths(context, &su, compiler_normalize_unit_path(context, file_name));
+	int fdlock = compiler_open_lock_file(su.wasm_name + ".lock", "compile-probe", true);
+	if(fdlock == -2)
+		return(true);
+	compiler_close_lock_file(fdlock);
+	return(false);
+}
+
 void unit_render(String file_name)
 {
 	unit_render(file_name, *context);

src/lib/compiler.h

@@ -17,6 +17,7 @@ void compile_shared_unit(Request* context, SharedUnit* su);
 SharedUnit* get_shared_unit(Request* context, String file_name);
 String compiler_error_page_unit(Request* context, String config_key);
 bool compiler_unit_compile_pending(Request* context, String file_name);
+bool compiler_unit_compile_in_progress(Request* context, String file_name);
 String compiler_site_directory(Request* context);
 StringList compiler_scan_site_units(Request* context);
 StringList compiler_list_known_units(Request* context);

src/wasm/backend.cpp

@@ -100,7 +100,7 @@ static bool wasm_artifact_exists(Request* context, const String& entry_unit)
 	// metadata mismatches, which can leave stale wasm with old imports.
 	bool source_missing = false;
 	if(compiler_unit_needs_recompile(context, entry_unit, &source_missing))
-		return(false);
+		return(compiler_unit_compile_in_progress(context, entry_unit));
 	if(source_missing)
 		return(false);
 	return(true);

src/wasm/worker.cpp

@@ -1606,7 +1606,7 @@ private:
 			return(1);
 		}
 
-		if(!file_exists_host(worker.unit_wasm_path(resolved)) || compiler_unit_needs_recompile(context, resolved, 0))
+		if(!file_exists_host(worker.unit_wasm_path(resolved)) || (compiler_unit_needs_recompile(context, resolved, 0) && !compiler_unit_compile_in_progress(context, resolved)))
 			get_shared_unit(context, resolved);
 
 		size_t unit_index = 0;