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01 server
Steve Perry edited this page Nov 2, 2015
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3 revisions
Start a local web server:
node server.js
or
nodejs server.js
In a browser
http://localhost:8888
In another shell
curl localhost:8888
Stop the local web server:
CTRL-C
Node.js comes with a bunch of libraries (that is, source code modules).
The code in this example requires the http module that comes with Node.js. For me this is in /usr/lib/nodejs/http.js.
We define an event handler named onRequest. We pass the event handler to the createServer function of the http module. The createServer function returns a Server object. The Server object is defined in /usr/lib/_http_server.js.
We call the listen method of the Server object. This starts a local web server listening on port 8888.
When the server calls our handler, it passes request and response. The request argument is an IncomingMessage object. The response argument is a ServerResponse object.
h = require("http");
function onRequest (request, response) {
response.writeHead(200, {"Content-Type": "text/plain"});
response.write("Hello Steve");
response.end();
}
srv = h.createServer(onRequest);
srv.listen(8888);
Note: JavaScript supports annonymous functions. We can compress the code like this:
var http = require("http");
http.createServer(function(request, response) {
response.writeHead(200, {"Content-Type": "text/plain"});
response.write("Hello World");
response.end();
}).listen(8888);
Find the process ID (PID) of the process started with the command node.
ps -C node
PID TTY TIME CMD
493 pts/1 00:00:00 node
List all processes.
ps aux
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
....
root 447 0.0 0.0 0 0 ? S< Oct21 0:00 [hd-audio0]
steve 493 0.0 0.2 701788 22524 pts/1 Sl+ 14:41 0:00 node server.js
steve 498 0.0 0.0 27084 5696 pts/10 Ss 14:41 0:00 bash
....
Show the process tree.
ps axjf
....
1723 31665 1869 1869 ? -1 Sl 1000 0:03 \_ gnome-terminal
31665 31673 1869 1869 ? -1 S 1000 0:00 | \_ gnome-pty-helper
31665 31674 31674 31674 pts/1 493 Ss 1000 0:00 | \_ bash
31674 493 493 31674 pts/1 493 Sl+ 1000 0:00 | | \_ node server.js
Attach the debugger (gdb) to process 493, which is the Node.js runtime.
sudo gdb -p 493
GNU gdb (Ubuntu 7.7.1-0ubuntu5~14.04.2) 7.7.1
...
Attaching to process 493
Reading symbols from /usr/bin/nodejs...(no debugging symbols found)...done.
...
[Thread debugging using libthread_db enabled]
...
38 ../sysdeps/unix/sysv/linux/x86_64/syscall.S: No such file or directory.
Traceback (most recent call last):
File "/usr/share/gdb/auto-load/usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.19-gdb.py", line 63, in <module>
from libstdcxx.v6.printers import register_libstdcxx_printers
ImportError: No module named 'libstdcxx'
(gdb)
Show the virtual address space of the process.
(gdb) info proc mappings
process 493
Mapped address spaces:
Start Addr End Addr Size Offset objfile
0x400000 0x11d2000 0xdd2000 0x0 /usr/bin/nodejs
0x13d1000 0x13d2000 0x1000 0xdd1000 /usr/bin/nodejs
0x13d2000 0x13eb000 0x19000 0xdd2000 /usr/bin/nodejs
0x13eb000 0x13f9000 0xe000 0x0
0x30f6000 0x338a000 0x294000 0x0 [heap]
...
0x7fc3b7984000 0x7fc3b8184000 0x800000 0x0 [stack:497]
0x7fc3b8184000 0x7fc3b8185000 0x1000 0x0
0x7fc3b8185000 0x7fc3b8985000 0x800000 0x0 [stack:496]
0x7fc3b8985000 0x7fc3b8986000 0x1000 0x0
0x7fc3b8986000 0x7fc3b9186000 0x800000 0x0 [stack:495]
0x7fc3b9186000 0x7fc3b9187000 0x1000 0x0
0x7fc3b9187000 0x7fc3b9987000 0x800000 0x0 [stack:494]
0x7fc3b9987000 0x7fc3b9b42000 0x1bb000 0x0 /lib/x86_64-linux-gnu/libc-2.19.so
0x7fc3b9b42000 0x7fc3b9d41000 0x1ff000 0x1bb000 /lib/x86_64-linux-gnu/libc-2.19.so
0x7fc3b9d41000 0x7fc3b9d45000 0x4000 0x1ba000 /lib/x86_64-linux-gnu/libc-2.19.so
0x7fc3b9d45000 0x7fc3b9d47000 0x2000 0x1be000 /lib/x86_64-linux-gnu/libc-2.19.so
0x7fc3b9d47000 0x7fc3b9d4c000 0x5000 0x0
0x7fc3b9d4c000 0x7fc3b9d65000 0x19000 0x0 /lib/x86_64-linux-gnu/libpthread-2.19.so
0x7fc3b9d65000 0x7fc3b9f64000 0x1ff000 0x19000 /lib/x86_64-linux-gnu/libpthread-2.19.so
0x7fc3b9f64000 0x7fc3b9f65000 0x1000 0x18000 /lib/x86_64-linux-gnu/libpthread-2.19.so
0x7fc3b9f65000 0x7fc3b9f66000 0x1000 0x19000 /lib/x86_64-linux-gnu/libpthread-2.19.so
0x7fc3b9f66000 0x7fc3b9f6a000 0x4000 0x0
0x7fc3b9f6a000 0x7fc3b9f80000 0x16000 0x0 /lib/x86_64-linux-gnu/libgcc_s.so.1
0x7fc3b9f80000 0x7fc3ba17f000 0x1ff000 0x16000 /lib/x86_64-linux-gnu/libgcc_s.so.1
0x7fc3ba17f000 0x7fc3ba180000 0x1000 0x15000 /lib/x86_64-linux-gnu/libgcc_s.so.1
0x7fc3ba180000 0x7fc3ba285000 0x105000 0x0 /lib/x86_64-linux-gnu/libm-2.19.so
0x7fc3ba285000 0x7fc3ba484000 0x1ff000 0x105000 /lib/x86_64-linux-gnu/libm-2.19.so
0x7fc3ba484000 0x7fc3ba485000 0x1000 0x104000 /lib/x86_64-linux-gnu/libm-2.19.so
0x7fc3ba485000 0x7fc3ba486000 0x1000 0x105000 /lib/x86_64-linux-gnu/libm-2.19.so
0x7fc3ba486000 0x7fc3ba56c000 0xe6000 0x0 /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.19
0x7fc3ba56c000 0x7fc3ba76b000 0x1ff000 0xe6000 /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.19
0x7fc3ba76b000 0x7fc3ba773000 0x8000 0xe5000 /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.19
0x7fc3ba773000 0x7fc3ba775000 0x2000 0xed000 /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.19
0x7fc3ba775000 0x7fc3ba78a000 0x15000 0x0
0x7fc3ba78a000 0x7fc3ba791000 0x7000 0x0 /lib/x86_64-linux-gnu/librt-2.19.so
0x7fc3ba791000 0x7fc3ba990000 0x1ff000 0x7000 /lib/x86_64-linux-gnu/librt-2.19.so
0x7fc3ba990000 0x7fc3ba991000 0x1000 0x6000 /lib/x86_64-linux-gnu/librt-2.19.so
0x7fc3ba991000 0x7fc3ba992000 0x1000 0x7000 /lib/x86_64-linux-gnu/librt-2.19.so
0x7fc3ba992000 0x7fc3ba995000 0x3000 0x0 /lib/x86_64-linux-gnu/libdl-2.19.so
0x7fc3ba995000 0x7fc3bab94000 0x1ff000 0x3000 /lib/x86_64-linux-gnu/libdl-2.19.so
0x7fc3bab94000 0x7fc3bab95000 0x1000 0x2000 /lib/x86_64-linux-gnu/libdl-2.19.so
0x7fc3bab95000 0x7fc3bab96000 0x1000 0x3000 /lib/x86_64-linux-gnu/libdl-2.19.so
0x7fc3bab96000 0x7fc3babb9000 0x23000 0x0 /lib/x86_64-linux-gnu/ld-2.19.so
0x7fc3bad9b000 0x7fc3bada2000 0x7000 0x0
0x7fc3badb6000 0x7fc3badb8000 0x2000 0x0
0x7fc3badb8000 0x7fc3badb9000 0x1000 0x22000 /lib/x86_64-linux-gnu/ld-2.19.so
0x7fc3badb9000 0x7fc3badba000 0x1000 0x23000 /lib/x86_64-linux-gnu/ld-2.19.so
0x7fc3badba000 0x7fc3badbb000 0x1000 0x0
0x7fff24a44000 0x7fff24a65000 0x21000 0x0 [stack]
0x7fff24b42000 0x7fff24b44000 0x2000 0x0 [vdso]
0x7fff24b44000 0x7fff24b46000 0x2000 0x0 [vvar]
0xffffffffff600000 0xffffffffff601000 0x1000 0x0 [vsyscall]
What's in the virtual address space of the nodejs process?
- nodejs executable
- libc-2.19.so
- libpthread-2.19.so
- libgcc_s.so.1
- libm-2.19.so
- libstdc++.so.6.0.19
- librt-2.19.so
- ld-2.19.so
- Heap space
- Stack space
- Portions of my app code (I think)
- Other
How big is the nodejs binary? About 14 MB.
steve@steve-home-1:/usr/bin$ ls -l node*
lrwxrwxrwx 1 root root 22 Oct 19 21:05 node -> /etc/alternatives/node
-rwxr-xr-x 1 root root 14592120 Oct 19 12:12 nodejs
What about some of the shared libraries?
libc-2.19.so is about 1.8 MB. librt-2.19.so is about 31 KB.
Notice that the nodejs process has a huge virtual address space: about 128 TB. But only small sections of the address space are actually used. Also notice that the nodejs executable and the shared libraries are mapped into the address space in sections.
What about threads? Is there only one thread?
(gdb) info threads
Id Target Id Frame
5 Thread 0x7fc3b9986700 (LWP 494) "V8 WorkerThread" sem_wait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/sem_wait.S:85
4 Thread 0x7fc3b9185700 (LWP 495) "V8 WorkerThread" sem_wait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/sem_wait.S:85
3 Thread 0x7fc3b8984700 (LWP 496) "V8 WorkerThread" sem_wait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/sem_wait.S:85
2 Thread 0x7fc3b8183700 (LWP 497) "V8 WorkerThread" sem_wait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/sem_wait.S:85
* 1 Thread 0x7fc3bad9c780 (LWP 493) "node" syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38
I didn't expect to see a bunch of threads. I read somewhere that nodejs was single threaded. Apparently ps doesn't show these as child processes. Let's look at the call stacks for a few threads.
(gdb) info stack
#0 syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38
#1 0x0000000000df1e3a in uv.epoll_wait ()
#2 0x0000000000defcd4 in uv.io_poll ()
#3 0x0000000000de0e86 in uv_run ()
#4 0x0000000000d67ec0 in node::Start(int, char**) ()
#5 0x00007fc3b99a8ec5 in __libc_start_main (main=0x6890a0 <main>, argc=2, argv=0x7fff24a622e8, init=<optimized out>, fini=<optimized out>,
rtld_fini=<optimized out>, stack_end=0x7fff24a622d8) at libc-start.c:287
#6 0x00000000006892cf in _start ()
(gdb) thread 2
[Switching to thread 2 (Thread 0x7fc3b8183700 (LWP 497))]
#0 sem_wait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/sem_wait.S:85
85 ../nptl/sysdeps/unix/sysv/linux/x86_64/sem_wait.S: No such file or directory.
(gdb) info stack
#0 sem_wait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/sem_wait.S:85
#1 0x0000000000df6898 in v8::base::Semaphore::Wait() ()
#2 0x0000000000dcd8a9 in v8::platform::TaskQueue::GetNext() ()
#3 0x0000000000dcd9fc in v8::platform::WorkerThread::Run() ()
#4 0x0000000000df7870 in ?? ()
#5 0x00007fc3b9d54182 in start_thread (arg=0x7fc3b8183700) at pthread_create.c:312
#6 0x00007fc3b9a8147d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111
(gdb) thread 3
[Switching to thread 3 (Thread 0x7fc3b8984700 (LWP 496))]
#0 sem_wait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/sem_wait.S:85
85 in ../nptl/sysdeps/unix/sysv/linux/x86_64/sem_wait.S
(gdb) info stack
#0 sem_wait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/sem_wait.S:85
#1 0x0000000000df6898 in v8::base::Semaphore::Wait() ()
#2 0x0000000000dcd8a9 in v8::platform::TaskQueue::GetNext() ()
#3 0x0000000000dcd9fc in v8::platform::WorkerThread::Run() ()
#4 0x0000000000df7870 in ?? ()
#5 0x00007fc3b9d54182 in start_thread (arg=0x7fc3b8984700) at pthread_create.c:312
#6 0x00007fc3b9a8147d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111
Recall that when we attached the debugger to nodejs, we got this:
Attaching to process 493
Reading symbols from /usr/bin/nodejs...(no debugging symbols found)...done.
Find a file that has symbols for nodejs.
apt-file find /usr/bin/nodejs
nodejs: /usr/bin/nodejs
nodejs-dbg: /usr/lib/debug/usr/bin/nodejs
sudo apt-get install nodejs-dbg
Attach the debugger.
ps -C node
PID TTY TIME CMD
7509 pts/1 00:00:00 node
sudo gdb -p 7509
…
Attaching to process 7509
Reading symbols from /usr/bin/nodejs...Reading symbols from /usr/lib/debug//usr/bin/nodejs...done.
The debugger found symbols in /usr/lib/debug/usr/bin/nodejs.
file /usr/lib/debug/usr/bin/nodejs
/usr/lib/debug/usr/bin/nodejs: ELF 64-bit LSB executable, x86-64, version 1 (SYSV),
dynamically linked (uses shared libs), for GNU/Linux 2.6.24, BuildID[sha1]=1b2ec93b51629fc6eda4ab241e4d0b84d6f69423,
not stripped
objdump --section-headers /usr/lib/debug/usr/bin/nodejs
…
26 .debug_aranges 00002310 0000000000000000 0000000000000000 000002e5 2**0
CONTENTS, READONLY, DEBUGGING
27 .debug_info 0004f906 0000000000000000 0000000000000000 000025f5 2**0
CONTENTS, READONLY, DEBUGGING