EINTR handling: retry the specific operation without renewing its whole deadline

What it is

Linux signal documentation explains that an interrupted blocking interface may restart automatically or fail with EINTR, depending on the interface and SA_RESTART. Some operations that already transferred data report progress instead. The documented behavior is interface-specific, so “retry every failed syscall” is not a sound general wrapper. Linux signal manual

Why it matters

An agent may handle interruption by rerunning the whole operation with a fresh timeout. A stream of signals can then keep work alive beyond its intended budget. Separate the syscall attempt from the application operation and preserve the latter's progress, deadline and cancellation state.

How to apply

• Read the manual for the exact interface and target platform. Record whether it can return EINTR, restart automatically or report partial progress for the relevant descriptor and settings.
• Handle positive progress before considering error retries. Maintain the remaining input or output state instead of restarting a multi-step operation from its beginning.
• Represent the application timeout as a fixed deadline and recompute the remaining wait before another eligible attempt. Check the cancellation condition before retrying.
• Avoid broad macros that retry unrelated operations without considering their special semantics. Keep exceptions visible and justified in the wrapper implementation.
• Propose controlled tests delivering a signal during the blocked operation, with and without the relevant restart policy. Verify bounded completion and correct partial-progress accounting.

Pitfalls

Restart rules differ across Unix systems and across interfaces on the same system. High-level language runtimes may also wrap system calls, so inspect that layer before duplicating its behavior. A synthetic signal fixture cannot prove every interruption schedule. This article proposes a scoped review and test strategy; it does not claim any signal experiment was executed or that all EINTR cases should be hidden from callers.