MINOR: threads: make MAX_THREADS configurable at build time

There's some value in being able to limit MAX_THREADS, either to save
precious resources in embedded environments, or to protect certain
deployments against accidently incorrect settings.

With this patch, if MAX_THREADS is defined at build time, it will be
used. However, given that LONGBITS is not a macro but is defined
according to sizeof(long), we can't check the value range at build
time and instead we need to perform the check at early boot time.
However, the compiler is able to optimize away the constant comparisons
and doesn't even emit the check code when values are correct.

The output message regarding threading support was improved to report
the number of threads.

diff --git a/include/common/hathreads.h b/include/common/hathreads.h
index 8e96e37e837d45a4dca0cfd93b669497ef518ecb..019d749703b56a9420875b3d5278ceffaefa4659 100644 (file)
--- a/include/common/hathreads.h
+++ b/include/common/hathreads.h
@@ -168,8 +168,11 @@ static inline unsigned long thread_isolated()
 #include <pthread.h>
 #include <import/plock.h>
 
+#ifndef MAX_THREADS
 #define MAX_THREADS LONGBITS
-#define MAX_THREADS_MASK ((unsigned long)-1)
+#endif
+
+#define MAX_THREADS_MASK (~0UL >> (LONGBITS - MAX_THREADS))
 
 #define __decl_hathreads(decl) decl
 

diff --git a/src/hathreads.c b/src/hathreads.c
index 39ff7e8288db241da85c6e10c22e56b338007b49..a21bddd9eafc4369efb3e21a6e01d91e46109ce1 100644 (file)
--- a/src/hathreads.c
+++ b/src/hathreads.c
@@ -108,13 +108,22 @@ void ha_rwlock_init(HA_RWLOCK_T *l)
 __attribute__((constructor))
 static void __hathreads_init(void)
 {
+       char *ptr = NULL;
+
+       if (MAX_THREADS < 1 || MAX_THREADS > LONGBITS) {
+               ha_alert("MAX_THREADS value must be between 1 and %d inclusive; "
+                        "HAProxy was built with value %d, please fix it and rebuild.\n",
+                        LONGBITS, MAX_THREADS);
+               exit(1);
+       }
+       memprintf(&ptr, "Built with multi-threading support (MAX_THREADS=%d).", MAX_THREADS);
+       hap_register_build_opts(ptr, 1);
+
 #if defined(DEBUG_THREAD) || defined(DEBUG_FULL)
        memset(lock_stats, 0, sizeof(lock_stats));
 #endif
 }
 
-REGISTER_BUILD_OPTS("Built with multi-threading support.");
-
 #else
 
 REGISTER_BUILD_OPTS("Built without multi-threading support (USE_THREAD not set).");