tic — Start a high-resolution stopwatch timer and optionally return a handle for paired toc reads.
tic starts a high-resolution stopwatch used by toc to report elapsed wall-clock seconds. Assign its opaque uint64 token when you need to measure from a specific start time.
Syntax
timerVal = tic()Returns
| Name | Type | Description |
|---|---|---|
timerVal | NumericScalar | Timer handle used by toc. |
Errors
| Identifier | When | Message |
|---|---|---|
RunMat:tic:StateLockFailed | Internal stopwatch state cannot be acquired. | tic: failed to acquire stopwatch state |
How tic works
- Uses the host's monotonic clock for nanosecond-resolution timing.
- Each call makes its start time the latest stopwatch.
tocwithout inputs can read that latest start repeatedly; it does not consume the timer. - Returns an opaque
uint64token. The bits identify a monotonic-clock instant and must not be treated as a numeric timestamp or duration. - Executes entirely on the CPU. There are no GPU variants because
ticinteracts with wall-clock state. - Calling
tocbeforeticraises the MATLAB-compatible errorRunMat:toc:NoMatchingTic.
Examples
Measuring a simple loop
tic;
for k = 1:1e5
sqrt(k);
end
elapsed = tocCapturing and reusing the tic handle
t = tic;
heavyComputation();
elapsed = toc(t)Nesting timers for staged profiling
outer = tic; % Keep the outer timer token
stage1(); % Work you want to measure once
inner = tic; % Start a second stopwatch
stage2();
innerT = toc(inner); % Elapsed time for stage2 only
outerT = toc(outer); % Elapsed time for both stagesMeasuring asynchronous work
token = tic;
future = backgroundTask();
wait(future);
elapsed = toc(token)Resetting the stopwatch after a measurement
elapsed1 = toc(tic); % Equivalent to separate tic/toc calls
pause(0.1);
elapsed2 = toc(tic); % Starts a new timer immediatelyUsing tic with coding agents
Open a RunMat example with live inputs, then ask the agent to explain how tic changes the result.
Run a small tic example, explain the result, then change one input and compare the output.
FAQ
Does tic print anything when called without a semicolon?⌄
No. tic is marked as a sink builtin, so scripts do not display the returned handle unless you assign it or explicitly request output.
Is the returned handle portable across sessions?⌄
No. The handle encodes a monotonic timestamp that is only meaningful within the current RunMat process. Passing it to another session or saving it to disk is undefined behaviour, matching MATLAB.
Can I run tic on a worker thread?⌄
Yes. Stopwatch state is process-wide, so concurrent scripts should retain and pass their own uint64 tokens when timings might interleave.
How accurate is the measurement?⌄
tic relies on a monotonic clock (via runmat_time::Instant), typically providing microsecond or better precision. The actual resolution depends on your operating system. There is no artificial jitter or throttling introduced by RunMat.
Does tic participate in GPU fusion?⌄
No. Timer builtins are tagged as CPU-only. Expressions containing tic are always executed on the host, and any GPU-resident tensors are gathered automatically by surrounding code when necessary.
Related Timing functions
Open-source implementation
Unlike proprietary runtimes, every RunMat function is open-source. Read exactly how tic is executed, line by line, in Rust.
- View the source for tic in Rust on GitHub
- Learn how the RunMat runtime works
- Found a bug? Open an issue with a minimal reproduction.
About RunMat
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