SHM lazy init is now configured in config.json (eclipse-zenoh#1756)

* SHM lazy init is now configured in config.json

* format fix

* review fixes

* fix typo

DEFAULT_CONFIG.json5

@@ -543,10 +543,20 @@
     /// NOTE: shared memory can be used only if zenoh is compiled with "shared-memory" feature, otherwise
     /// settings in this section have no effect.
     shared_memory: {
+      /// Whether shared memory is enabled or not.
+      /// If set to `true`, the SHM buffer optimization support will be announced to other parties. (default `true`).
+      /// This option doesn't make SHM buffer optimization mandatory, the real support depends on other party setting.
       /// A probing procedure for shared memory is performed upon session opening. To enable zenoh to operate
       /// over shared memory (and to not fallback on network mode), shared memory needs to be enabled also on the
       /// subscriber side. By doing so, the probing procedure will succeed and shared memory will operate as expected.
       enabled: true,
+      /// SHM resources initialization mode (default "lazy").
+      /// - "lazy": SHM subsystem internals will be initialized lazily upon the first SHM buffer
+      /// allocation or reception. This setting provides better startup time and optimizes resource usage,
+      /// but produces extra latency at the first SHM buffer interaction.
+      /// - "init": SHM subsystem internals will be initialized upon Session opening. This setting sacrifices
+      /// startup time, but guarantees no latency impact when first SHM buffer is processed.
+      mode: "lazy",
     },
     auth: {
       /// The configuration of authentication.

commons/zenoh-config/src/defaults.rs

@@ -307,7 +307,10 @@ impl Default for LinkRxConf {
 #[allow(clippy::derivable_impls)]
 impl Default for ShmConf {
     fn default() -> Self {
-        Self { enabled: true }
+        Self {
+            enabled: true,
+            mode: ShmInitMode::default(),
+        }
     }
 }
 

commons/zenoh-config/src/lib.rs

@@ -548,9 +548,19 @@ validated_struct::validator! {
             pub shared_memory:
             ShmConf {
                 /// Whether shared memory is enabled or not.
-                /// If set to `true`, the SHM buffer optimization support will be announced to other parties. (default `false`).
+                /// If set to `true`, the SHM buffer optimization support will be announced to other parties. (default `true`).
                 /// This option doesn't make SHM buffer optimization mandatory, the real support depends on other party setting
+                /// A probing procedure for shared memory is performed upon session opening. To enable zenoh to operate
+                /// over shared memory (and to not fallback on network mode), shared memory needs to be enabled also on the
+                /// subscriber side. By doing so, the probing procedure will succeed and shared memory will operate as expected.
                 enabled: bool,
+                /// SHM resources initialization mode (default "lazy").
+                /// - "lazy": SHM subsystem internals will be initialized lazily upon the first SHM buffer
+                /// allocation or reception. This setting provides better startup time and optimizes resource usage,
+                /// but produces extra latency at the first SHM buffer interaction.
+                /// - "init": SHM subsystem internals will be initialized upon Session opening. This setting sacrifices
+                /// startup time, but guarantees no latency impact when first SHM buffer is processed.
+                mode: ShmInitMode,
             },
             pub auth: #[derive(Default)]
             AuthConf {
@@ -634,6 +644,14 @@ pub enum QueueAllocMode {
     Lazy,
 }
 
+#[derive(Default, Debug, Clone, Copy, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum ShmInitMode {
+    Init,
+    #[default]
+    Lazy,
+}
+
 impl Default for PermissionsConf {
     fn default() -> Self {
         PermissionsConf {

commons/zenoh-shm/src/init.rs

@@ -0,0 +1,29 @@
+//
+// Copyright (c) 2024 ZettaScale Technology
+//
+// This program and the accompanying materials are made available under the
+// terms of the Eclipse Public License 2.0 which is available at
+// http://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
+// which is available at https://www.apache.org/licenses/LICENSE-2.0.
+//
+// SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
+//
+// Contributors:
+//   ZettaScale Zenoh Team, <zenoh@zettascale.tech>
+//
+
+use crate::{
+    api::client_storage::GLOBAL_CLIENT_STORAGE,
+    cleanup::CLEANUP,
+    metadata::{storage::GLOBAL_METADATA_STORAGE, subscription::GLOBAL_METADATA_SUBSCRIPTION},
+    watchdog::{confirmator::GLOBAL_CONFIRMATOR, validator::GLOBAL_VALIDATOR},
+};
+
+pub fn init() {
+    CLEANUP.init();
+    GLOBAL_CLIENT_STORAGE.init();
+    GLOBAL_METADATA_STORAGE.init();
+    GLOBAL_METADATA_SUBSCRIPTION.init();
+    GLOBAL_CONFIRMATOR.init();
+    GLOBAL_VALIDATOR.init();
+}

commons/zenoh-shm/src/lib.rs

@@ -54,6 +54,7 @@ macro_rules! tested_crate_module {
 pub mod api;
 mod cleanup;
 pub mod header;
+pub mod init;
 pub mod metadata;
 pub mod posix_shm;
 pub mod reader;

zenoh/src/net/runtime/mod.rs

@@ -172,6 +172,9 @@ impl RuntimeBuilder {
             .unwrap_or_else(|| load_plugins(&config));
         // Admin space creation flag
         let start_admin_space = *config.adminspace.enabled();
+        // SHM lazy init flag
+        #[cfg(feature = "shared-memory")]
+        let shm_init_mode = *config.transport.shared_memory.mode();
 
         let config = Notifier::new(crate::config::Config(config));
         let runtime = Runtime {
@@ -231,6 +234,12 @@ impl RuntimeBuilder {
             }
         });
 
+        #[cfg(feature = "shared-memory")]
+        match shm_init_mode {
+            zenoh_config::ShmInitMode::Init => zenoh_shm::init::init(),
+            zenoh_config::ShmInitMode::Lazy => {}
+        };
+
         Ok(runtime)
     }
 }

zenoh/tests/shm.rs

@@ -195,6 +195,20 @@ async fn test_session_pubsub(peer01: &Session, peer02: &Session, reliability: Re
     }
 }
 
+#[test]
+fn zenoh_shm_startup_init() {
+    // Open the sessions
+    let mut config = zenoh::Config::default();
+    config
+        .transport
+        .shared_memory
+        .set_mode(zenoh_config::ShmInitMode::Init)
+        .unwrap();
+    tokio::runtime::Runtime::new().unwrap().block_on(async {
+        let _session = ztimeout!(zenoh::open(config)).unwrap();
+    });
+}
+
 #[test]
 fn zenoh_shm_unicast() {
     tokio::runtime::Runtime::new().unwrap().block_on(async {