fix: Make TLS initialization thread-safe and idempotent using pthread_once #11090
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ThomasBrady
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edsiper,
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koleini
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WalkthroughRefactored thread-local storage (TLS) initialization across Fluent Bit by introducing conditional macro patterns and idempotent initialization using Changes
Sequence Diagram(s)sequenceDiagram
participant Init as Initialization Code
participant Once as pthread_once
participant Key as TLS Key
participant InitFunc as Init Function
rect rgb(200, 220, 240)
Note over Init,InitFunc: Old: Direct initialization (unsafe race)
Init->>Key: Direct pthread_key_create()
end
rect rgb(240, 200, 220)
Note over Init,InitFunc: New: pthread_once pattern (thread-safe)
Init->>Once: Call FLB_TLS_INIT(key)
Once->>Once: pthread_once(&once_ctl, init_func)
Once->>InitFunc: Call init function (once)
InitFunc->>Key: pthread_key_create()
Once-->>Init: Return (subsequent calls are no-ops)
end
Estimated code review effort🎯 3 (Moderate) | ⏱️ ~20 minutes
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✨ Finishing touches
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… once for each key Signed-off-by: Thomas Brady <[email protected]>
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📒 Files selected for processing (4)
include/fluent-bit/flb_log.h(1 hunks)include/fluent-bit/flb_output.h(1 hunks)include/fluent-bit/flb_scheduler.h(1 hunks)include/fluent-bit/flb_thread_storage.h(1 hunks)
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🧬 Code graph analysis (4)
include/fluent-bit/flb_output.h (1)
src/flb_log.c (1)
FLB_TLS_DEFINE(50-56)
include/fluent-bit/flb_thread_storage.h (1)
src/flb_log.c (1)
FLB_TLS_DEFINE(50-56)
include/fluent-bit/flb_log.h (1)
src/flb_log.c (1)
FLB_TLS_DEFINE(50-56)
include/fluent-bit/flb_scheduler.h (1)
src/flb_log.c (1)
FLB_TLS_DEFINE(50-56)
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Comment on lines
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| #define FLB_TLS_DEFINE(type, name) \ | ||
| pthread_key_t name; \ | ||
| pthread_once_t name##_once = PTHREAD_ONCE_INIT; \ | ||
| void name##_init_func(void) { \ | ||
| pthread_key_create(&name, NULL); \ | ||
| } |
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Handle pthread_key_create failure to avoid undefined TLS state.
With the new pthread_once wrapper we only invoke pthread_key_create() once. If that call returns an error (e.g. EAGAIN, ENOMEM), the key stays uninitialized but the pthread_once guard prevents any retry, so every later FLB_TLS_SET/GET will operate on an invalid key and the failure is silent. Before this change we at least retried on the next FLB_TLS_INIT, so this is a regression in resiliency. Please capture the return code, surface/log it, and keep the caller from proceeding (e.g. by storing the status in a companion variable that FLB_TLS_INIT checks and aborts or reports). That way we fail fast instead of running with a broken TLS slot.
🤖 Prompt for AI Agents
In include/fluent-bit/flb_thread_storage.h around lines 57 to 62, the
pthread_key_create() result is ignored so if it fails the pthread_once guard
prevents retries and TLS key remains uninitialized; modify the macro to capture
the return code from pthread_key_create into a companion int status variable
(e.g. name##_init_rc), set it atomically, and have
FLB_TLS_INIT/FLB_TLS_GET/FLB_TLS_SET check that status and abort/log/return an
error when non-zero; also log the errno/rc when pthread_key_create fails to
surface the root cause and avoid proceeding with an invalid key.
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Upstreaming as requested by @cosmo0920.
Background:
flb_reload()callsflb_create()to create a new context for validation.flb_create()callsflb_log_create()which callsFLB_TLS_INIT(flb_worker_ctx). On platforms withoutFLB_HAVE_C_TLSdefined (e.g. Windows),FLB_TLS_INITdirectly callspthread_key_create.FLB_TLS_INITis also called from multiple other locations (flb_lib.c,flb_worker.c, etc.). Each call topthread_key_createwith the same key is undefined behavior per POSIX, causing issues like fluentbit logs not being output after a halted reload.Summary of changes
This patch makes FLB_TLS_INIT(key) idempotent using pthread_once:
Before: Each FLB_TLS_INIT call directly executed pthread_key_create, causing multiple key creations
After: Each FLB_TLS_INIT uses pthread_once to ensure the key is created exactly once, regardless of how many times or from where it's called
flb_log.h,flb_output.h,flb_scheduler.h) to use correct declaration patternThis ensures thread-safe, idempotent TLS initialization across all compilation units and during hot reload, eliminating the undefined behavior.
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If this is a change to packaging of containers or native binaries then please confirm it works for all targets.
ok-package-testlabel to test for all targets (requires maintainer to do).Documentation
Backporting
Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.
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