thread pool and queue

[icing]

• new source files for thread pool and queue
• test cases 3300 and 3301 for them
• internal documentation

[icing]

@bagder ready for merge, next in line. Will continue on Monday with the other ones.

[bagder]

@aisle-analyzer

[aisle-research-bot]

🔒 Aisle Security Analysis

We found 1 potential security issue(s) in this PR:

#	Severity	Title
1	🔵 Low	Invalid timespec in Curl_cond_timedwait() can cause pthread_cond_timedwait EINVAL and busy-loop DoS

See details in the comment below.

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Analyzed PR: #20916 at commit d8a11c0

_{Last updated on: 2026-03-21T22:01:31Z}

[bagder]

💯

[Copilot]

Pull request overview

Adds new internal thread pool (Curl_thrdpool) and thread queue (Curl_thrdq) implementations to support asynchronous work item processing, along with unit tests and internal documentation.

Changes:

• Introduce lib/thrdpool.* and lib/thrdqueue.* plus build integration.
• Add unit tests unit3300/unit3301 and register them in the test harness.
• Extend tracing/threads infrastructure (condvar wrappers + Curl_trc_feat_infof) and add internal documentation.

Reviewed changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated 14 comments.

Show a summary per file

File	Description
tests/unit/unit3301.c	Adds unit tests for thread queue behavior (send/process/recv + event callback).
tests/unit/unit3300.c	Adds unit tests for thread pool behavior (min/max threads, signaling, destroy modes).
tests/unit/Makefile.inc	Registers new unit test sources in the unit test bundle.
tests/data/test3301	Adds test case metadata for unit3301.
tests/data/test3300	Adds test case metadata for unit3300.
tests/data/Makefile.am	Registers new test case data files for distribution.
lib/thrdqueue.h	Defines the thread queue API and callbacks.
lib/thrdqueue.c	Implements the thread queue using llist + thread pool.
lib/thrdpool.h	Defines the thread pool API and callbacks.
lib/thrdpool.c	Implements the thread pool with worker slots, signaling, and idle waiting.
lib/curl_threads.h	Adds cross-platform condition-variable types and APIs under USE_MUTEX.
lib/curl_threads.c	Implements cross-platform condition-variable wrappers (signal/wait/timedwait).
lib/curl_trc.h	Declares Curl_trc_feat_infof() for feature-based verbose logging.
lib/curl_trc.c	Implements Curl_trc_feat_infof().
lib/memdebug.c	Ensures memdebug cleanup unlocks after closing the logfile.
lib/Makefile.inc	Adds new lib sources/headers to the build source lists.
docs/internals/THRDPOOL+QUEUE.md	Documents thread pool/queue design, operation, and safety notes.
docs/Makefile.am	Registers the new internal documentation page.

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