The State Machine Your async Method Compiles Into
An async method that never suspends allocates nothing. The same method, suspended once, allocates 160 bytes. The cost is not the keyword — it is the suspension.
Async in production · Part 1
Long-form · since 2026
C#, .NET, and the runtime beneath them.
Long-form technical writing about the CLR, the JIT, the garbage collector and the frameworks built on top.
- Articles
- 11
- Series
- 05
- Written by
- Callum Reeve
The Delegate Is Optional. The Display Class Is Not
A lambda that captures an int allocated 24 bytes on .NET 10.0.12; the same lambda reading a constant allocated none. The delegate was optional, the display class was not.
A Shared lock Cost the Same as a Private One at One Thread, and Not at Two
On .NET 10.0.12 a shared lock matched a per-thread lock at one thread and cost more from two up, where Monitor.LockContentionCount left zero.
The Query EF Core Writes When You Ask for a Count
On EF Core 10.0.12, AsEnumerable() before Where().Count() sent a full-table SELECT instead of COUNT(*) and allocated 1056.36 KB against 49.53 KB at 1,000 rows.
clrstack Shows the Waiter and syncblk Names the Lock Holder
In a dotnet-dump of a contested lock, clrstack -all marked no thread as the owner. syncblk named it, and a suspended await appeared only in dumpasync.
A Container Given 1.2 CPUs Tells the Runtime It Has 2
Environment.ProcessorCount is the CPU quota rounded up, never below 1. The thread pool minimum follows it, and Server GC switches itself off at 1.
The Box You Pay For Is the One That Escapes
Assigning a struct to an interface allocated 0 bytes. Passing it across a call boundary allocated 24. A constrained generic allocated none, until its body asked for an object.
02
Series
Multi-part investigations, in reading order.
- Async in productionWhat `async` compiles into, what it costs at runtime, and the failure modes that only appear once real load is on the thread pool.
- Allocation and escapeWhere an object actually goes, what the JIT can keep off the heap, and how much of the difference survives contact with production code.
- .NET in a containerWhat the runtime detects about a cgroup, the GC and thread-pool defaults it derives from that, and the footprint those defaults produce.
- Reading the diagnosticsDumps, counters and traces the runtime already emits, read directly rather than pattern-matched against folklore.
- The shape of a requestWhat an ASP.NET Core request costs at each stage of its path, measured at the runtime level rather than described at the API level.
- Multi-part investigations, in reading order.
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