Limit thread count in router config and add note to configs

Signed-off-by: Yadunund <[email protected]>

rmw_zenoh_cpp/config/DEFAULT_RMW_ZENOH_ROUTER_CONFIG.json5

@@ -186,7 +186,14 @@
           backoff: 100,
           // Number of threads dedicated to transmission
           // By default, the number of threads is calculated as follows: 1 + ((#cores - 1) / 4)
-          // threads: 4,
+          // We limit the number of threads that the zenoh session can spin to 1.
+          // Without this limit, applications with multiple zenoh sessions can
+          // encounter system resource errors when trying to create new threads.
+          // Once zenoh migrates to relying on tokio for its async runtime,
+          // see https://github.com/eclipse-zenoh/zenoh/pull/566, we can consider
+          // removing these flags since with tokio, zenoh can better manage the threads it spins
+          // with the help of thread pools.
+          threads: 1,
         },
       },
       /// Configure the zenoh RX parameters of a link

rmw_zenoh_cpp/config/DEFAULT_RMW_ZENOH_SESSION_CONFIG.json5

@@ -187,6 +187,13 @@
         },
         // Number of threads dedicated to transmission
         // By default, the number of threads is calculated as follows: 1 + ((#cores - 1) / 4)
+        // We limit the number of threads that the zenoh session can spin to 1.
+        // Without this limit, applications with multiple zenoh sessions can
+        // encounter system resource errors when trying to create new threads.
+        // Once zenoh migrates to relying on tokio for its async runtime,
+        // see https://github.com/eclipse-zenoh/zenoh/pull/566, we can consider
+        // removing these flags since with tokio, zenoh can better manage the threads it spins
+        // with the help of thread pools.
         threads: 1,
       },
       /// Configure the zenoh RX parameters of a link

zenoh_c_vendor/CMakeLists.txt

@@ -15,7 +15,8 @@ find_package(ament_cmake_vendor_package REQUIRED)
 # the zenoh session can spin via the session config as well as the ASYNC_STD_THREAD_COUNT
 # environment variable. Without this limit, applications with multiple zenoh sessions can
 # encounter system resource errors when trying to create new threads.
-# Once zenoh migrates to relying on tokio for its async runtime, we can consider
+# Once zenoh migrates to relying on tokio for its async runtime,
+# see https://github.com/eclipse-zenoh/zenoh/pull/566, we can consider
 # removing these flags since with tokio, zenoh can better manage the threads it spins
 # with the help of thread pools.
 # Note: We separate the two args needed for cargo with "$<SEMICOLON>" and not ";" as the